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Ken,
<br>
<br>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.
<br>
<br>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?

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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.
<br>
<br>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.
<br>
<br>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.


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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 .

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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.
<br>
<br>cartridges with .30-06 case head:
<br>at 54,000 lb/sq in. - - - - - 8,432 lb
<br>at 70,000 lb/sq in. - - - - - 10,390 lb
<br>
<br>cartridges with H&H Magnum case head:
<br>at 54,000 lb/sq in. - - - - - 10,045 lb
<br>at 70,000 lb/sq in. - - - - - 13,022 lb
<br>
<br>cartridges with Weatherby .378 case head:
<br>at 54,000 lb/sq in. - - - - - 12,929 lb
<br>at 70,000 lb/sq in. - - - - - 16,760 lb
<br>
<br>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:
<br>.30-06 -- 0.156 sq in.
<br>H&H -- 0.186 sq in.
<br>Weatherby -- 0.239 sq in.
<br>
<br>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.
<br>
<br>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.
<br>
<br>Just one more reason I don't consider loading to the hottest pressures the practice of a smart shooter.


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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.
<br>
<br>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?

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"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?"
<br>
<br>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.
<br>
<br>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.
<br>
<br>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.)
<br>
<br>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.


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"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. "
<br>
<br>"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.
<br>
<br>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.


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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.
<br>
<br>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).
<br>
<br>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.
<br>
<br>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.
<br>
<br>final comparison -- maximum Swift versus optimum Howell loads:
<br>powder charge - - - Swift 39.3 gr - - - Howell 54.0 gr
<br>velocity - - - Swift 3,400 ft/sec - - - Howell 3,500 ft/sec
<br>peak pressure - - - Swift 65,250 lb/sq in. - - - Howell 51,430 lb/sq in.
<br>
<br>differences -- the .220 Howell
<br>
<br>-- uses 14.7 grains more powder (instead of 18.1 gr more that it'd need to equal the SAAMI maximum for the Swift)
<br>
<br>-- gets 100 ft/sec more velocity (instead of 360 ft/sec if loaded to SAAMI maximum for the Swift)
<br>
<br>-- at 13,820 lb/sq in. less pressure (instead of the same barrel-burning pressure as the Swift)
<br>
<br>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.
<br>
<br>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.


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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.
<br> The drawback I see would be the higher powder charge would generate more recoil. Probably only a problem with the heavy hitters. E

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Ken,
<br>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.


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Ken,
<br>
<br>I'm confused(it happens alot).
<br>
<br>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.)".
<br>
<br>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?
<br>
<br> I don't/can't savvy that.
<br>
<br>Also,why wouldn't a soft loaded 22-284(62grs H2O capacity),not replicate performance you mention,but in a shorter/stiffer action?......................
<br>
<br>


Brad says: "Can't fault Rick for his pity letting you back on the fire... but pity it was and remains. Nothing more, nothing less. A sad little man in a sad little dream."
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"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?"
<br>
<br>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.
<br>
<br>"Also,why wouldn't a soft loaded 22-284(62grs H2O capacity),not replicate performance you mention,but in a shorter/stiffer action?"
<br>
<br>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.
<br>
<br>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.
<br>
<br>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.
<br>
<br>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.
<br>
<br>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.


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Ken,
<br>
<br>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.
<br>
<br> 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.
<br>
<br>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?
<br>
<br>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?
<br>
<br>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?
<br>
<br>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?
<br>
<br>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?
<br>
<br>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......................


Brad says: "Can't fault Rick for his pity letting you back on the fire... but pity it was and remains. Nothing more, nothing less. A sad little man in a sad little dream."
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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.
<br>
<br>As I recall, the overflow capacities of the .220 Swift and the .220 Howell are 47 and 62 grains of water.
<br>
<br>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!)


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Ken,
<br>
<br>I very much appreciate your taking the time,to try and get my mind right!
<br>
<br>Allow me to simplify,as you have answered much of what puzzled me.
<br>
<br>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?
<br>
<br>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?
<br>
<br>Obliged......................


Brad says: "Can't fault Rick for his pity letting you back on the fire... but pity it was and remains. Nothing more, nothing less. A sad little man in a sad little dream."
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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.
<br>
<br>Another similar question to help me clarify the concept.
<br>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.
<br>
<br>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.

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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.
<br>
<br>A couple of points by Dr.Howell that surprised me are;
<br>
<br>#1- The 284win is a piss poor case design that is weaker than '06 based cartridges.
<br>
<br>#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.
<br>
<br>Facinating......James


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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.
<br>
<br>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.
<br>
<br>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.
<br>
<br>I need more hard data on throat erosion from this .220 H. theory. Meanwhile I will stay with the PPC theory.
<br>
<br>I do not care about "efficiency" however. Horsepower per liter or a little extra powder used are not important factors to me.
<br>
<br>In summary I will stay will full loads with slow burning powders.

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Don,
<br>
<br>I'm just trying to understand what the good Doctor has been trying to tell me.
<br>
<br>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.
<br>
<br>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)
<br>
<br>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.
<br>
<br>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.
<br>
<br>But I'm ALL ears.............
<br>
<br>


Brad says: "Can't fault Rick for his pity letting you back on the fire... but pity it was and remains. Nothing more, nothing less. A sad little man in a sad little dream."
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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.
<br>
<br>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.
<br>
<br>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.
<br>
<br>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....................


Brad says: "Can't fault Rick for his pity letting you back on the fire... but pity it was and remains. Nothing more, nothing less. A sad little man in a sad little dream."
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