Prudent pressure in modern rifles

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Ken,
 
 As I mentioned on another thread, I'm planning on turning the 35 whelen ackley into a 350 Rigby Magnum. Quickload shows that the rigby will push a 250 gr @ 2700 fps @ 50 kpsi, the whelen ackley does it at high 60's. I would live w/ 250's @ 2400-2500 but the whelen just won't group at that level. I also like the way the more gently tapered case feeds.
 
 Anyhow, I know you've mentioned it on the old board, but what do you consider a good working pressure for modern bolt guns, 50-55 kpsi?

Influenced heavily by the very logical reasoning and findings of my mentor the late Homer S Powley, I've learned that a working peak pressure of 45,000 to 47,500 copper units is about the best, all around, for cartridges that SAAMI used to rate at 50,000 to 55,000 copper units. SAAMI now rates these cartridges at 60,000 to 65,000 lb/sq in.
 
 There's no rigid relationship between copper units and lb/sq in., of course, so we can only approximate what this pressure is, in lb/sq in. A good approximation is about 50,000 to 55,000 lb/sq in. -- an approximation, not an exact equivalent in different units.
 
 At these pressure levels, muzzle velocities increase and decrease very little with significant increases and decreases in pressure -- so there's little gain with higher pressures, little loss with lower pressures. And the differences in trajectory, impact energy, penetration, and expansion are too slight to discern in the real world.

Should we be thinking in terms of gross chamber pressure , or maybe looking more at the actual bolt thrust ? It seems to me that is the critical point to look at when thinking about how much you are stressing your rifle's action . I think maybe it gives you some additional leeway if you stick to 06 head sized cartridges , and it might be a greatly overlooked disadvantage of the RUM and WSM offerings . I think it also might expain how people have been getting away with some of the extremely hot loadings you see them using , especially in some of the improved chamberings .

I've been looking at bolt thrust (force) for a long time, and it gets scary in a hurry. A few years ago, I compared the bolt thrusts of three cartridge-head diameters at different peak pressures. Here are some figures.
 
 cartridges with .30-06 case head:
 at 54,000 lb/sq in. - - - - - 8,432 lb
 at 70,000 lb/sq in. - - - - - 10,390 lb
 
 cartridges with H&H Magnum case head:
 at 54,000 lb/sq in. - - - - - 10,045 lb
 at 70,000 lb/sq in. - - - - - 13,022 lb
 
 cartridges with Weatherby .378 case head:
 at 54,000 lb/sq in. - - - - - 12,929 lb
 at 70,000 lb/sq in. - - - - - 16,760 lb
 
 As a methodological basis, I took 90 percent of each head diameter as the estimated net piston diameter for each case -- 0.470 for the '06, 0.513 for the H&H, and 0.582 for the big Weatherby. This methodological assumption gave me these net piston areas for these case heads:
 .30-06 -- 0.156 sq in.
 H&H -- 0.186 sq in.
 Weatherby -- 0.239 sq in.
 
 This means that there may be (and probably is) some minor difference between my estimates and the actual web areas. But all I was after was an estimate that would show the general magnitude of the trend, not a split-gnat-hair actual measure of the force involved in each case. Also, this methodological estimate, I believe, mutes the actual increase in force -- IOW, if 90 percent of the .30-06 head diameter is net web area acting as a piston, the net piston areas of the H&H and the big Weatherby are a slightly higher and a still higher percentage of their respective head diameters.
 
 These calculations show that the SAME pressure in cases with smaller and larger head diameters exerts lesser and greater forces on the breech face -- and in a bolt action, on the locking lugs, which don't get bigger or stronger with a rechambering or rebarreling.
 
 Just one more reason I don't consider loading to the hottest pressures the practice of a smart shooter.

Ken...an example would be very informative. For example pick a cartridge like the 7mm Rem Mag and provide pressures for what a reloading manual would call a "starting load" and show velocity and pressure for each increment to what they would call "max"...that way the increase in pressure for increase in velocity could be seen. I assume you would have to do this with a "model" of some type as I don't believe I've ever seen anything quite like this in print.
 
 Also a question about your 220 Howell...if it uses more powder, at a lesser pressure, to out perform the 220 Swift how is it on barrel life when compared to a Swift?

"if it uses more powder, at a lesser pressure, to out perform the 220 Swift how is it on barrel life when compared to a Swift?"
 
 If you'll read my earlier post -- really study it and absorb all its points -- you'll see the answer right there. I listed those five principles of interior ballistics separately in my post, but they're integral to a single system and to each other. Like someone said about truth, they're indivisible.
 
 When the .220 Howell is loaded to lower pressures than the Swift factory load (and typical Swift handloads), those lower pressures guarantee slower throat erosion. The substantially larger case accommodates larger charges, which produce more propelling gas, which in turn produces higher velocities.
 
 If I loaded the .220 Howell to the same pressures as the Swift, throat erosion in the .220 Howell would occur as rapidly as it does in the Swift. (And the muzzle velocity would of course be even greater than either the Swift's or my "economy cruise" velocities.)
 
 My larger case is enough larger to let me increase my powder charge (compared with the Swift) without going to the limit that my larger case can accommodate.

"an example would be very informative. For example pick a cartridge like the 7mm Rem Mag and provide pressures for what a reloading manual would call a "starting load" and show velocity and pressure for each increment to what they would call "max"...that way the increase in pressure for increase in velocity could be seen. I assume you would have to do this with a "model" of some type as I don't believe I've ever seen anything quite like this in print. "
 
 "Models" and samples abound in the handloading manuals. All you have to do (you can do it yourself) is to study the loads for, say, the .300 Savage and the .30-06, or the .30-06 and the .300 Winchester Magnum, or the .250 Savage and the .25-06, or the .280 Remington and the 7mm Remington Magnum, even the .22 Hornet or the .223 Remington and the .220 Swift.
 
 But you'll have to shed the typical handloader's practice of tunnel-gazing at only the maximum loads listed for each cartridge. Notice instead how often the hottest loads for the smaller cartridge use less powder than the suggested starter loads in the larger cartridge. Also compare velocities, and you'll often find exactly what I've been trying to describe and explain -- that a moderately larger charge in a significantly larger case can propel the same bullet to a higher velocity at a lower pressure.

Here's a comparison to illustrate how the principles I've been trying to explain (above) work together in two comparable but different cartridges. The bullet (80-gr Sierra) and the barrel length (26 in.) are the same for both cartridges.
 
 In the .220 Swift, a charge of 39.3 grains develops a peak pressure of about 65,250 lb/sq in. and drives the bullet out the muzzle at about 3,400 ft/sec (I say "about" because I'm rounding-off the pressure and velocity figures. And this charge really pushes the SAAMI maximum of 65,000 lb/sq in. for the Swift).
 
 The .220 Howell requires a charge of 57.4 grains to develop a peak pressure of about 65,000 lb/sq in. and a velocity of about 3,760 ft/sec.
 
 But by loading the .220 Howell with only 54.0 grains, I can get 3,500 ft/sec with a peak pressure no higher than 51,400 lb/sq in.
 
 final comparison -- maximum Swift versus optimum Howell loads:
 powder charge - - - Swift 39.3 gr - - - Howell 54.0 gr
 velocity - - - Swift 3,400 ft/sec - - - Howell 3,500 ft/sec
 peak pressure - - - Swift 65,250 lb/sq in. - - - Howell 51,430 lb/sq in.
 
 differences -- the .220 Howell
 
 -- uses 14.7 grains more powder (instead of 18.1 gr more that it'd need to equal the SAAMI maximum for the Swift)
 
 -- gets 100 ft/sec more velocity (instead of 360 ft/sec if loaded to SAAMI maximum for the Swift)
 
 -- at 13,820 lb/sq in. less pressure (instead of the same barrel-burning pressure as the Swift)
 
 With a pressure margin here of about 14,000 lb/sq in., you can see that I can increase the .220 Howell charge and get a little more velocity, and still be a good bit shy of the SAAMI maximum pressure.
 
 But this would work against me more than for me. The increase in peak pressure would increase the rate of throat erosion, while the negligible flattening of the trajectory wouldn't be noticeable even at long range.

Very interesting point of view. I also like having a flexible velocity level. You need only 3400 fps. If your rifle doesn't shoot well with one powder, you can try another and still be quite close to what you need. Or even try a little more, if that's what the rifle requires for best accuracy.
 The drawback I see would be the higher powder charge would generate more recoil. Probably only a problem with the heavy hitters. E

Ken,
 458Lott mentioned a phenomenon that afflicts one of my rifles too & I am interested in your take on this. It is a Model 7 Youth in .243Win that only starts to group decently with a warm load. Littlebit & I were talking about it and theorized (dangerous thing for me to do [Linked Image]

) that this rifle may have a bedding problem. It takes 42 grns of IMR 4350 behind a 100grn Partition to make it MOA or better. Interestingly, the POI shifts drastically with reduced (recommended starting loads according to the Speer Manual) and grouping opens to more than 4". The POI is approximately 4-6" lower at 100 yds with a starting load (about 37.5grns IMR 4350) Your thoughts on this? thank you, badger.

Ken,
 
 I'm confused(it happens alot).
 
 You state:"If I loaded the .220 Howell to the same pressures as the Swift, throat erosion in the .220 Howell would occur as rapidly as it does in the Swift. (And the muzzle velocity would of course be even greater than either the Swift's or my "economy cruise" velocities.)".
 
 Does that infer,that a 223 loaded at 65K PSI,erodes throats on the same order as the .220 Howell at 65K PSI? Despite significant differences in propellant charge weights?
 
 I don't/can't savvy that.
 
 Also,why wouldn't a soft loaded 22-284(62grs H2O capacity),not replicate performance you mention,but in a shorter/stiffer action?......................

"Does that infer,that a 223 loaded at 65K PSI,erodes throats on the same order as the .220 Howell at 65K PSI? Despite significant differences in propellant charge weights?"
 
 Exactly. At a given pressure (and by association, its given temperature), the barrel absorbs the same heat from the powder gas, and the throat erodes at whatever rate it erodes at that pressure and temperature.
 
 "Also,why wouldn't a soft loaded 22-284(62grs H2O capacity),not replicate performance you mention,but in a shorter/stiffer action?"
 
 It would. But I don't like or trust high-pressure cases with rebated rims. They're weaker where they need to be as strong as possible. A case with a rebated rim can blow gas backward more readily than a full rimless case.
 
 I bought the remains of an exploded rifle that shows frighteningly what wild gas can do. (It'll be a permanent display at the Powley Center.) The barrel seems to have suffered no damage from the greatly overloaded cartridge. The wildly excessive peak pressure poked quite a hole out the back of the case even though the case is a full rimless, not a rebated-rim case.
 
 But the receiver and stock are collections of large and small pieces, and my friend luckily has only one minute speck of brass in his face (too small to be any trouble or worth going after) and had to have only one larger chunk dug out of his face. The barrel and largest pieces of the action went YARDS in several directions.
 
 As I said, the case is rimless. The peak pressure was a Mount Everest, not an anthill. This event would've been even more likely if the case had had a rebated rim.
 
 So I don't base any of my cartridge designs on the .284 unless it's for someone who specifically insists on using it as his parent case. Even then, I resist.

Ken,
 
 I just reread your July 2000 article,in VH. You went to great lengths to make comparative studies(with vastly different projectile weights/profiles),but deleted the KEY ingredient,if I'm understanding things correctly? Case capacity.
 
 For all of these numbers to jive,one must know the case capacities,of the cartridges compared. Especially for someone as dense as I,to get it to all sink in.
 
 What I could extrapolate,was a guess,from a "hint" you made regarding capacity. "In the tests that these figures came from,the bullet with the 0.440 BC is 75 percent heavier than the one with only 0.242 BC and is fired from a cartridge with about 25 percent more powder capacity than the second cartridge in the test". So my brain tells me a Swift(cartridge case used in your comparison,for those who don't have the article) is of about 46grs H20 and a 25% increase on that volume,yields 57.5grs or so for the .220 Howell?
 
 So if capacity is the sole issue(as opposed to radical proprietary case design),what is novel in this cartridge,that hasn't been continually realized?
 
 Wouldn't a "soft" loaded 22CHeetah do the same(my R/P 243Win formed cases,hold 55.9grs H2O). Or the 22-6mmAI,22-284,22-06,22-240Wby,etc?
 
 In a quick twisted barrel and utilizing the same 80gr projectile,where do these cartridges stand in comparison to your new cartridge. That including speed/pressure/throat errosion comparisons?
 
 My question is,is there more to this than having "excess" capacity and loading it to sedate pressures,via slowish burning propellants? Or is their some MOJO going on,in regards to a specific case design? That,regardless of many cases,have a like capacity value?
 
 I guess that is the issue I'm having trouble clarifying. I hope I didn't muddle this,as you have my undivided attention and curiousity......................

Stick, I'm absolutely bushed tonight -- don't have the capacities right in front of me and don't feel like struggling to my feet and staggering over to the shelves. So I'm going to give you a couple of figures from the top of my bald ol' noggin.
 
 As I recall, the overflow capacities of the .220 Swift and the .220 Howell are 47 and 62 grains of water.
 
 To be absolutely honest with you, Pard, I simply can not see why anyone has any difficulty understanding all this. You're not unique in being puzzled, so I'll keep trying to make it clear to you. Keep asking. I don't expect to ALWAYS be as shot as I am tonight. (Still haven't done even the first of my three half-hours on the exercise bike, either!)

Ken,
 
 I very much appreciate your taking the time,to try and get my mind right!
 
 Allow me to simplify,as you have answered much of what puzzled me.
 
 Are all cases that hold 70grs of H2O(as an example),created equally? Or is there "hidden" interior ballistics,working to favor one case design over the other,regardless of like capacities?
 
 To clarify. Would a 70gr capacity '06 based case,70gr capacity H&H based case and 70gr capacity Rem Ultra based case,share like velocities and errosion characteristics,at like pressures,assuming like diameter projectiles/weights?
 
 Obliged......................

With respect to Big Stick's post and your response concerning throat erosion....as I carefully read it you said (paraphrasing) that if you had a .223 and a .220 Swift both loaded to 65,000psi the throat erosion would be the same...if this is the case, what is all the hype about a cartridge being "over-bore" which I take to mean uses more powder than can be effectively used and it is this that causes throat erosion.
 
 Another similar question to help me clarify the concept.
 Assume I have a load that operates at 65,000psi and all I do is seat the bullet out a little further (assuming I can safely do that and not cause additional pressure that way)...as I undertand it I have basically made the interior of the case "bigger" and pressures should drop or conversely I could add more powder to get the pressure back up to 65,000psi and get more velocity.
 
 Before you take me to the wood shed again for trying to play at the "max velocity" level, let me assure you I much prefer a lower operating level with respect to pressure as a margin of safety.....I firmly believe if you want "more" to go to a bigger case.

One of the most interesting threads I have ever read on any Forum. I am as guilty as anybody in trying to get max velocity out of a particular cartridge but am starting to see the folly in this. This year I have been using a low pressure load for deer hunting and haven't noticed any reduction in terminal performance.
 
 A couple of points by Dr.Howell that surprised me are;
 
 #1- The 284win is a piss poor case design that is weaker than '06 based cartridges.
 
 #2- Pressure and Temperature is what erodes throats,not large charges of powder. So a 300 win mag barrel could last longer than say a 308win,if the 300mag was loaded to 50k pressure and the 308min was loaded to 65k pressure. Even though the 300mag was still outperforming the 308 by a large margin.
 
 Facinating......James

This large case-low pressure theory goes against the latest trend of the PPC design of the short fat case. It also results in less than full cases that might result in secondary explosions as Ackley found with reduced loads and slow powders. I have found that in some rifles reduced loads are not as accurate.
 
 As to the .284 Winchesters rebated rim. It looks wrong to me so I don't want one. However the failures from cases seem to occur at the web and not at the base of the cartridge. So my complaint is only subjective. But I do think the popularity of "magnums" is in some part due to the strong "looking" case.
 
 I designed my "big" .224" on the belted magnum back when the PPC was the craze. The case is 2" long with a .300" neck and the standard taper and shoulder. In reflection this is fun but has resulted in nothing much more than what a K-Swift would have done with the same twist bbl.
 
 I need more hard data on throat erosion from this .220 H. theory. Meanwhile I will stay with the PPC theory.
 
 I do not care about "efficiency" however. Horsepower per liter or a little extra powder used are not important factors to me.
 
 In summary I will stay will full loads with slow burning powders.

Don,
 
 I'm just trying to understand what the good Doctor has been trying to tell me.
 
 Load density is easily handled with the wide spectrum of slow burning powders. I can easily understand how you can have a "reduced" load,by utilizing much slower propellants than generally encountered,in a given case design.
 
 You could shoot 240gr MK's in a 308 case with Re-25 and have 100% load density,with reduced pressure. I very much understand that,but it goes against EVERYTHING I personally believe in.(grin)
 
 The last point I was hoping to have clarified,was the benefits of various case designs,in regards to internal ballistics. I'm hoping Ken had a good nights sleep and is ready to relate his thoughts,on that matter.
 
 I've trouble seeing that my 308Win at like pressures,will erode throats on the same order as a 30-378 at like pressure. That goes against every tidbit,that every Highpower/BR shooter has ever related to me.
 
 But I'm ALL ears.............

Forgot a couple things,that I've found contrary. First,the 284Win case design. I can understand those that are "afeared" of a rebated design. No problem there. But I KNOW firsthand,that the W/W brass is hell for stout in that cartridge. It has a very thick web and thick sidewalls. Simply put,it is a brute.
 
 I'm on the first 100pcs of brass,for each of my 25-284's. I've yet to lose a case to split necks,incipient seperation or managed to enlarge a primer pocket. Rest assured,that I am NOT guilty of the reduced load train of thought.
 
 Simply put,the 284 brass that I've used,rates amongst the most rugged case design that I've played with. In fact,nothing has lasted as long,being subjected to soooo much. Primer pockets are soft,looooong before now.
 
 I'd be curious to hear about the particular action that scattered,as I can't fathom a brass issue,assuming proper chamber/die geometry. Unless,he received a bogus lot,that contradicts examples I have used....................

Don,
 
 You wrote.."This large case-low pressure theory goes against the latest trend....It also results in less than full cases that might result in secondary explosions....."
 
 I have been using this large case-low pressure theory with my hunting loads this year and have been well satisfied,trend bucker or not.
 
 The key for me is to use a powder that is a "click" or two slower than normal. This results in 100% loading density or slightly compressed. I don't think anyone is suggesting one use a very slow powder with 50% loading density a let it rattle around in the case.
 
 In summary,I too,will stay with full loads of slow burning powders. Just at a lower pressure and temperature [Linked Image]

Let me put a twist on this topic and assume that pressure and heat combined have the same effect on like metals, regardless of application. We can assume that a rifle chamber is the same as an engine combustion chamber and a like bore size can be affected by increasing its length or stroke. We can now make a comparison. BMEP is used in our trade as a measure of peak pressure. We can take an engine of the same bore size and increase the stroke length (chamber area). Now if we want to make the same power with the shorter stroked engine we must raise the peak cylinder pressure.The side effect of this if we are using like metals is the increased heat and pressure will cause increased erosion to the piston crown and valve seat surfaces. This fact remains the same regardless of engine size or horsepower.
 Enough of that. Ken is talking about throat erosion, this is a direct result of peak pressure and temperature and has nothing to do with attainable velocities, which are ideally gained by a constant pressure over the full length of the bbl.
 By reducing the 220 Howell to below the peak loaded pressure of a 22 Hornet, throat erosion should be less assuming the same cylinder temperures are achieved, which they likely are not as we are not trying to get the same power level. If we compare apples to apples and use the Howell cartridge to duplicate 22-250 or Swift velocities then I would agree throat erosion will be less and pressures can be reduced significantly and the same velocities will be achieved.

"This large case-low pressure theory goes against the latest trend of the PPC design of the short fat case."
 
 Not at all. The ratio of case diameter to case length is an entirely different design consideration that doesn't matter here.
 
 "It also results in less than full cases that might result in secondary explosions as Ackley found with reduced loads and slow powders."
 
 Nope. You've assumed "facts" not in evidence. The larger case uses a slower powder -- with benefits that I didn't present in the discussion of the other comparison. The pressure curve in the .220 Howell compares very interestingly with the Swift's curve. The Swift's curve rises quickly to a higher and sharper pressure peak, then fades rapidly as the bullet scoots toward the muzzle. The .220 Howell's curve rises more slowly to a significantly lower peak, then fades much more slowly with bullet travel. The PEAK pressure (read "erosion") is lower in the .220 Howell, while its AVERAGE pressure (read "acceleration") is higher, clear out to the muzzle.
 __________________________________
 
 "Overbore" is a word used often, understood seldom. My cartridges are not over bore capacity for the powders that I designed them around.
 
 "Bore capacity" applies to a cartridge in relation to available powders. A case that's "over bore capacity" is a case that can not be loaded with a caseful of any available powder without developing dangerous pressures. It's a matter of how fast and how high the pressure curve rises while the travel of the bullet down the bore bleeds-off some of the pressure. In a case that's over bore capacity, the travel of the bullet down the bore can not relieve the building pressure fast enough to keep the peak pressure (from a caseful charge) down to a safe level.
 
 If there's a powder available that you can fill the case with, without producing dangerous pressures, that case is not "over bore capacity."
 
 When I started loading rifle ammo in the early 'Fifties, IMR-4350 and H-4831 were the slowest powders available. Both are too fast for the .220 Howell -- i e, the .220 Howell is over bore capacity for these powders (just as the .223 is over bore capacity for Bullseye). It is NOT, however, over bore capacity for IMR-7828, Ramshot Magnum, and several other powders in this burning-rate class. I could fill my .220 Howell with Hodgdon's ultra-slow 50BMG powder and not even come close to optimum pressures. I couldn't pack, jam, or stomp enough 50BMG into the .220 Howell to raise pressures to a good operating level -- so the .220 Howell is clearly NOT "over bore capacity" for all available powders.
 
 As I've already posted somewhere, this isn't just nerd theory. It's all long-proven fact, clearly presented in classic interior-ballistics literature that unfortunately isn't available to the average shooter. So of course it's all "new" to you and seems to run counter to what you already know about what goes on inside the rifle. But the fact that it's new, and negates some of your understanding, does NOT mean that it's wrong. I'm not putting anybody down. Just the opposite -- I'm trying to share what I'm learning in intense study of interior ballistics.

If I use a .220 Swift and you use a 30-06 necked to .224 you will use about 20 grs more powder per shot. At the 5000 shot mark I will have saved $285 which should pay for a new barrel!
 
 I still have to find out more about this .220 H . So far it's hard to believe.
 
 But more powder costs more, gives more recoil and more blast. And it does go against the modern trend of the low aspect ratio cartridges like the PPC and now the .300 WSM and SAUM.

Then the perfect answer is dog-simple, Bro' Don --
 
 You shoot a .220 Swift, and I'll shoot a .220 Howell, and we'll both be happy.

Ken,
 
 I hear you loud and clear on this. It jibes perfectly with my experience over almost forty years of loading. In fact, right now I am looking forward to taking advantage of just this principle in a 270 rifle I am having rechambered to 270 Wby. It already gives me almost 3200 fps with a certain charge of H450 from a 24" bbl.
 
 After the rechambering the same charge will obviously give me less velocity, because the case capacity will be increased. Increasing the charge will bring the velocity back up, even though the pressure may be lower. Going to an even slower powder, say Re 22, Re 25 or 7828, one should be able to get higher velocities still, without primer pockets expanding, etc.
 
 The fly in this ointment, of course, is that the increased head area will increase the bolt thrust or force the locking lugs must bear.
 
 Ted

Ken, thanks for sharing your thoughts, and please continue doing so. I have learned a fair amount off of this thread. You have a vast amount of knowledge, that is for sure. I didn't know exactly what over bore capacity was before, nor did I know that pressure was what is responsible for ruining bores, not velocity. Ken, are there any over bore capacity cartridges that you are aware of for normal speed rifle powders? Such as IMR 4064, IMR 3031, powders within that range more or less. Thanks.

"Ken, are there any over bore capacity cartridges that you are aware of for normal speed rifle powders? Such as IMR 4064, IMR 3031, powders within that range more or less."
 
 Yes, the world's full of cartridges that are over bore capacity for the powders you mention, including those that aren't over bore capacity in the generic sense that there's NO powder that they can safely fire by the caseful.
 
 Just for example, I plugged IMR-3031 into the computer to see what pressure a caseful of it would churn-up in my .220 Howell with an 80-grain Sierra -- over 113,000 lb/sq in.!
 
 I should add that the optimum powder for any case depends on (a) the net capacity of the case, between the web and the base of the seated bullet, (b) the maximum average peak operating pressure desired, and (c) the weight of the bullet. In a given case, for example, the heavier bullets would generally call for a somewhat slower powder -- and the lighter bullets a somewhat faster one. How easily the bullet can be pushed down the bore -- or how stubbornly its mass resists propulsion -- affects how the powder behaves.
 
 Since I designed my .220 Howell strictly for 75- to 80-grain (and heavier) bullets, I centered the design on IMR-7828 -- and sure enough, IMR-7828 is one of the two or three best powders for it WITH THESE BULLETS. I'm not interested in using anything lighter in it (yet), so I haven't considered anything lighter for it. It may NOT be over bore capacity for IMR-4831 or IMR-4350 or even something a little quicker, with the lightest .224 bullets. I suspect that it isn't, but I just haven't looked into that question at all.

Woah Nellie-- I have tried my best to wade through this entire post and in my limited way understand it. I don't. I sort of feel like the old story about the little girl who was going to give a school report on Penguins. Her preface was " I don't want to teach you more about Penguins than you want to know,".
 What is beyond my understanding is how in the world you are going to blow a third more powder with its attendant ejecta through the same size hole even at lower pressure and not wear out that hole as fast as less ejecta at higher pressure. There is more of it that has to go through there and it all has to go big charge or little high pressure or low. We are not talking about just sedately running it through either. Real time it is going through there A. D. Q. no matter what. That hole in the barrel is going to get real hot real quick either way and the hotter it gets the softer the steel gets and easier to scrub away.
 Just looks like to me if you run more of it at less or less of it at more sort of balances out the same.
 Must be magic but the higher forms of mathmatics are magic to me anyway. What am I missing here and please keep it simple. Remember the Penguins.
 BCR

Ahem, uh Dr. Howell,
 
 I asked a question or two earlier in this thread not exactly pertinent to the thread although an earlier poster had mentioned the same phenomenum. Should I re-post these questions in a separate thread or was my post simply overlooked? [Linked Image]

. Thanks, badger.

Gotcha, Badger -- yes, I missed your question altogether.
 
 "It is a Model 7 Youth in .243Win that only starts to group decently with a warm load. Littlebit & I were talking about it and theorized that this rifle may have a bedding problem. It takes 42 grns of IMR 4350 behind a 100grn Partition to make it MOA or better. Interestingly, the POI shifts drastically with reduced ... loads ... and grouping opens to more than 4". The POI is approximately 4-6" lower at 100 yds with a starting load (about 37.5grns IMR 4350) Your thoughts on this?"
 
 I think you may be right -- that you have a bedding problem. That much variation in POI can't be blamed on the difference in muzzle velocity, and the variation of group size strongly suggests bad variation in the barrel's vibration pattern.
 
 You may also have a related problem -- the torque on the action screws may be partly to blame. They may be too loose, too tight, or too unevenly tight.
 
 If it were my rifle, I'd glass-bed it, probably with pillars to boot, and make sure that the fore-end didn't touch the barrel anywhere. Then I'd invest in a good torque wrench (I bet you know exactly where you can lay your hands on one!) and mess around with the torque on the action screws.
 
 For a bedding compound, a number of the bench-rest gang recommend Charley Robertson's Pro-Bed 2000 (http://www.scorehi.com/scorehi/home.htm). I bought some but haven't used it yet, so I don't know how much better it may be than the good ol' Acraglas and Acraglas gel I used so much of in years gone by.

Boggy, ol' buddy, I think maybe the solution to your confusion may lie in the distinction between heat (in Btu) and temperature (in �F). Consider two logs of the same species of pine (your choice -- longleaf, shortleaf, slash, loblolly, or whatever else), exactly the same length and diameter.
 
 Imagine (a) shredding one log into excelsior and striking a match to it, and (b) letting the other lie in the woods and rot. Both logs will put out the same number of Btu, but of course over strikingly different spans of time. Only a brass monkey or a cigar-store Indian lacks the imagination to see that the �F levels of the two are drastically different.
 
 The high peak temperature concomitant with a high peak pressure, whatever the weight of the charge, is what affects the throat adversely. Lower that temperature, and even the far minor scrubbing action of the powder granules has less effect on the surface of the steel. Also, with the higher peak pressure, the increase in the temperature of the steel is more localized -- more tightly focused -- in the throat and early rifling.
 
 At a lower peak temperature, a higher heat output (Btu) can be absorbed along more of the barrel's length without anything like the adverse effect of the higher peak temperature at the throat.
 
 I've heated our homes with fuels from corn cobs to coal, natural gas, bottle gas, fuel oil, and several kinds of wood. It's been easy to notice that woods put out more heat (Btu) at lower temperatures (�F) and thus heat the house more evenly, and that some of the pitchier pines put out about the same amount of heat at higher temperatures. Good stove-fuel hardwoods (e g, oak) burn at much "cooler" �F than the pitchier pines but put out as much or more heat.
 
 As I think I've already mentioned, the larger charge of a slower powder in my .220 Howell produces a lower peak pressure (therefore temperature) more gradually, and the gas thus produced maintains its pressure higher and longer. The peak is lower, longer, and less sharp, and the downslope is much less steep. So the larger charge does indeed produce more HEAT but at a significantly lower peak pressure and TEMPERATURE.
 
 I hope this makes this mess a bit clearer to you -- but I bet that now somebody else in our crowd is more confused than he was.

Thank you. I am going to try a different stock (Big Stick is sending me a Synthetic one) & will see how it shoots before doing any bedding work with a new stock. Just want to see if the same characteristics with regards to POI shift & loads apply. badger.

I think I got a handle on the why as to how a .300 super magnum loaded at 55,000 psi burns out barrels faster than a .308 loaded to 60,000 psi. You're saying that basically, the .300 super magnum at lower pressure produces lower temperatures more spread out over time, rather than a higher temperature that burns out. I think I get it now......

If you said what you meant and meant what you said (" ... a .300 super magnum loaded at 55,000 psi burns out barrels faster than a .308 loaded to 60,000 psi."), you got it exactly backward. It's HIGH PRESSURE and its related high temperature that burns-out barrels faster. So the smaller cartridge loaded to a higher pressure burns barrels out faster than the larger cartridge loaded to a lower pressure.

I,too,think "I got it".But then I think I saw Elvis at the Fort Worth Stock Show yesterday,too!

Ken, I mean the .308 would burn out barrels quicker, thanks for noticing!

Thank you right on for the answer you gave, Ken. I sort of understand that explanation. Sort of the same difference heating steel with a rosebud tip and a pinpoint.
 Still not sure it is going to make a lot of difference in the cosmic scheme of things but at least I know what you are talking about and it stands to reason.
 BCR

I'm glad I stumbled in here, I think I actually managed to learn something again.
 
 If I understand this correctly, high pressures erode, but what we perhaps did not explicitly state, is that the "over bore" cartridges have high pressure for a long(er) duration. A 308 has high pressure, same as 30-378, but is at near-max pressure (temp) for a much shorter duration than the large cap case. In other words, time x temperature are the function.
 
 If you take the extreme temperature down, you can increase the time exposure, and still reduce erosion.
 
 At least, that's what I think I just learned. FWIW, Dutch.

Dutch,don't you dare leave here!Ken often talks smarter than I can listen.An interpreter is exactly what I need.I realize one can "dumb things down" only so far and still transmit meaningful information,but a large gap is still left with me when Ken is thru dumbing something down!much obliged.

" ... a large gap is still left with me when Ken is thru dumbing something down!"
 
 "Dumbing something down?" Naaaaaaaah! Explaining. Clarifying. NOT for dumb guys.
 
 Early in his career, one of the two best Bible teachers I've ever known (Bob Mumford -- Derek Prince is the other) developed his ability to make spiritual truths crystal clear by teaching retarded people.
 
 One of my jobs at Saudi Arabian Airlines' Flight Crew Ground Training Center (Jeddah, 1984-1985) was editing the several editions of the Recurrent Training Bulletins for the Boeing 7xx series, the L-1011, and the Airbus -- for Saudi flight crews to study and understand -- including writing exam questions at the end of each article for Saudis to understand and answer for grading. Believe me, there's more to writing good test questions than you may first guess!
 
 By comparison, you guys are a pleasure -- including y'all who think you're dumb.
 
 The only real handicap I see here isn't innate inability at all -- but the insistence that anything new has to fit what you already "know" -- because a lot of what you "know" is not accurate. This is harder to deal with -- for you and for me -- than mere mental weakness.
 
 The sincere desire to learn is your greatest asset -- whatever your IQ may be.
 
 Years ago, a friend told me of an episode when he was working his way through the university as a janitor. Working nights, he picked-up a lot -- randomly -- by studying whatever had been left on the board in whatever class room he was cleaning.
 
 While he was cleaning one class room one night, the professor came in to get or do something at his desk. As the prof was leaving, my friend asked him about something on the board that puzzled him. The prof waved him off.
 
 "Oh, you can't understand that," he said (or something to that effect) and left. Then he came back.
 
 "It just dawned on me that my job here is to make things like this clear enough that you CAN understand them." He proceeded to explain, and my friend did understand.
 
 That prof was my kind of guy! And the kind of prof I always tried to be when I was teaching.

Ken.....I think it was Mark Twain who said "It isn't what you don't know that will hurt you, it's what you think you know and don't"...true today as it was back then.

I don't remember that from Twain (my thesis figure in my Master's curriculum). He did borrow and use differently the essence of this quotation from Josh Billings:
 
 "The trouble with people is not that they don't know but that they know so much that ain't so."
 
 I think it was Billings who wrote one of my favorites -- "They say that love is blind, and that may be so, but I know some guys in love who see more in their gals than I do."

I think this is Twain or Will Rogers:" Nothing dumber than an educated man if you get him off what he's educated on." Please correct me if I'm wrong.It sounds more like Josh Billings.gene