Home Forums Hunting & Shooting Ask The Gunwriters Pressure vs. Powder capacity

Ken I wonder if you could clarify something that I have read on some of your previous posts. You have indicated that you think that barrel wear is directly related to the pressure generated by a load. Thus a 7mm STW loaded to 7mm Rem Mag velocity would produce less pressure and thus less barrel wear despite the fact that a milder STW load will still use more powder than a maximum Rem Mag load. I certainly like this theory better since I shoot mild loads in my STW, but I have read a lot of people who attribute barrel wear to the amount of powder vs. the size of the bore. Have you had experience where using mild loads you have gotten great barrel life out of cartridges with a barrel eating reputation?
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<br>I appreciate any insights you could share with me.
<br>
<br>Rick

You bring up five related but distinctly different basic properties of powders burning in cartridges. Look at the fundamentals (none of this is dreamt-up theory, BTW. It's all discerned and repeatedly confirmed fact):
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<br>First -- in a case with a given net capacity, larger charges of a given powder produce higher pressures.
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<br>Second -- In a larger case, a larger charge is necessary to produce the same level of pressure that the smaller charge produces in the smaller case.
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<br>Third -- at a given level of pressure, a smaller bore erodes faster than a larger bore (a .224 barrel erodes faster -- with fewer rounds fired -- than a .243 barrel if both the .224 and the .243 produce the same peak pressure). Like everything else involved here, this occurs in a mathematically calculable ratio.
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<br>Fourth -- powder produces velocity -- more powder produces more velocity. The amount of propelling gas produces velocity, whatever the peak pressure may be.
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<br>Five -- given the above, if larger Case B requires (for example) 10% more powder to produce the pressure that the smaller Case A produces, loading Case B with only 5% more powder can produce higher velocity at a lower pressure than Case A would require.
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<br>Given the huge variety of cartridges available for each bullet caliber, it isn't necessary to load a cartridge to SAAMI maximum pressures and above to get even the highest velocities safely available in the smaller cartridge. This is the "secret" of my .220 Howell, which uses a little more powder than the .220 Swift (for more velocity) in a 25% to 30% larger combustion cavity (for lower pressure, therefore slower throat erosion).
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<br>I wish this set of interlocking interior-ballistics principles weren't so widely unknown among serious handloaders. They're certainly easy enough to understand -- easier by far to exploit.

Thank you for your response. It seems that this would lead to the conclusion that you are better off buying say a .300 RUM than a .300 Win Mag (all other things being equal) because you can create lower pressure loads that will provide longer barrel life at the same velocity, and you laways have the option to go faster if the need arises. I am glad to hear it, because this is certainly not what most people believe.
<br>
<br>Thanks,
<br>Rick

Rick,
<br>
<br>That is exactly what I am looking by changing from my 375 H&Hs to 375 RUM.
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<br>I think the key is to settle on a level of performance. In my case the 375 H&H is my caliber for for everything.
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<br>Now the 375 RUM will deliver top end H&H ballistics:
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<br>1) At much lower pressure.
<br>
<br>2) It will deliver top H&H ballistics with a far wider range of powders or much wider range of loading parameters. This in turn should increase the chances of getting top accuracy across a wider range of bullets.
<br>
<br>3) If I want, I could shoot 270 grainers at over 3000 or the new 260 grain Nosler Ballistic tips at over 3100 f/s. So in a manner of speaking, the 375 RUM offers another gear or two to use if I so "choose"
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<br>4) In the 375 H&H, I often use 39 grains of one of our Australian powders which I think Hodgdon sell as H4227 Extreme, with 220 Hornady flat noses. I would expect with the 375 RUM to be able to retain that performance level and with top accuracy with perhaps 43 grains or similar of the same powder.
<br>
<br>However there are some other considerations.
<br>
<br>For example, some might say "then why not use a 378 Wby"
<br>
<br>Well, I have owned 2 of them (I am a slow learner).
<br>
<br>Now in this case certain rifle limitations are imposed because of the 378 case size. Also the very large case and enormous freebore, makes mid range loads difficult as small hangfires can be the order of the day.
<br>
<br>Low pressures also seem to result in a degree of accuracy that is less fussy. For example, rifles with bedding problems will frequently shoot well with low pressure loads.
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<br>I hope in the next month or two to test a 300 Ultra and load through from 308, 30/06 and 300 Win ballistics.
<br>
<br>Mike
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<br>Mike,
<br>
<br>We had similar ideas from reading Dr.Howell's posts. I have used the 338 winmag for several years with great results but operated at high pressure. I had a 338 Ultra built 2.5 years ago and did considerable load development with it.
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<br>I settled on what I called my "Ken Howell Load" and have used it this year with sterling results. It is a 185gr XLC loaded with H-1000(which is considered too slow a powder) and it lumbers along at 3300fps. Using a faster powder,such as V-N560,one can get 3500fps but at much higher pressure.
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<br>This load is faster than a 338 win mag can achieve and does it at much lower pressure and temperature. This barrel should last longer than 338wm barrel operating at higher pressure.
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<br>Even with this reduced load,I'm still getting top end velocity compared to a 300 Ultra with a 180gr XLC but at low(relatively) pressure.
<br>
<br>Good luck with your 375 Ultra...James
<br>

James,
<br>
<br>Over the years I have lots of loads that might be called mid range. This has been a product of liking big bores and with our high volume shooting out her.
<br>
<br>One area I am keen for on the 375 Ultra (and similar would apply to the 338 Ultra) is to develop loads aorund the powder you call Varget.
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<br>For example, the H&H is generally around the 69 to 72 grains of Varget with 270 grain bullet for the 2600 to 2650 f/s area.
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<br>I would estimate that a 375 Ultra would probably top out at maybe 82 grains of Varget or a bit more with 270 grainers. That would probably produce a velocity about 100 f/s less than its full potential, say about 2900 f/s with 270 grainers.
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<br>So I am thinking I can maybe work around the 75 grain mark and duplicate the H&H with lower pressure and with charges not much bigger and also avoid the heavy boom one often gets with large low pressure loads of slower powders.
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<br>With 338 and 375 Ultras, if you take H&H and Win Mag ballistics as the benchmark, there are almost a limitless number of charges and type of pwders you can use to duplicate these ballistics.
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<br>It is almost like the Ultras give you the full steet in which to find a good place but the 338 Win and 375 H&H only allow you to look at one end of the street. You just have to be able to find a better house if you have the full steet to choose from
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<br>Mike
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Ken, interesting comments. Have your 5 points been
<br>reduced to a Formula? Which actually might be
<br>easier for me to understand. I wonder if your
<br>comments could be tied to accurary as I have hear
<br>a shorter case is more accurate, ie 7.62 nato, round.
<br>
<br>

The following tables may look like a "dirty trick" but the natural inherent nature of this board takes a normally orderly spread sheet and indiscriminately eliminates spacings and columns and re-positions everything to the left margin. But, the tables illustrate the various characteristics of various powders. Some will produce 48,000 to 60,000 CUP with 60 grains of powder and others will produce about the same CUP with 45 grains!!! The gist of this exercise was to extract some consistency but none was found. Some powders will be #1 in some category but not in another. For example one powder will be #1 in CUP @ grain but not #1 in FPS @ grain.
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<br>When discussing various aspects of a rifles or cartridges performance there is a general tendency to refer generically to "powder". Can't do that and be explicit at the same time!
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<br>Barrel burners usually have one thing in common. They have large case capacities and small bores. Supplementing what was already said earlier, ( and elsewhere ) a common garden hose nozzle illustrates velocity. If it is removed completely the flow is relatively slow and voluminous. Screw on the nozzle and then adjust it. The more you close it the higher the jetting stream effect is.
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<br>Powder burns at a temperature far above the melting point of steel. Those who have used a blow torch, butane torch, brazing torch, welding ( oxy-acetylene ) or cutting torch know what happens. When cutting you first hold the torch stationary and heat the metal to a glow. Then you press a lever to introduce a high pressure stream of oxygen which blasts the molten metal away. Steel melts at a few hundred degrees centigrade. Powder burns at 3,000 degrees centigrade.
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<br>Two things occur thermically to a barrel. The rifling's, which are exposed, vulnerable, ridges, are melted and blasted by hot gas and sand blasted with pellets of gunpowder. *( When engraving a granite tombstone the lettering is formed by blasting the granite with black abrasive sand which eats it away). The barrel/chamber heat checks and forms cracks and fissures in the steel which are very visible. More powder means more heat - longer and bigger cases with smaller barrels mean higher velocities coming out of the cases neck and impinging on the "leade" - ( the ends of the rifling ). The erosion of the rifling and its "advancement" up the barrel can be monitored using a Stoney Point gauge.
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<br>High pressures and "hot loads" are also doing an insidious, damaging "job" on the guns components. In addition to the chamber swelling, and retracting, ( expanding the fissures and cracks ) the bolt lugs are being "kicked" back against the stops repeatedly. Eventually, over time, imperceptibly, a head space problem will develop. The gunstock is taking a pounding as well internally where steel is in contact with wood. ( Some of the BIG loudenboomers will split and destroy the stock )
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<br>We hear a lot about reloaders loading various powders in a quest for the "best, tightest, group, but almost never hear them searching for a powder that will give velocity with reduced pressure or the same pressure with less recoil. In the recoil formula the powder grains are asked for. If some powders require 60 grains for a given pressure and some only require 45 grains for the same pressure, wouldn't that normally be an aspect to look at? It certainly shows up in the formulas and the resulting answers mathematically.
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<br>If the (anonymous ) theory is to use a larger case to produce the same velocity with less pressure, then wouldn't it be a giant step forward to use a powder that also gave the same pressure with fewer grains. ( That would be a "double dip, or two scoop, of goodies" ). Or less pressure with the same grains!
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<br>Load Study 30-06 Springfield
<br>180 Grain Jacketed boattail bullet
<br>
<br>First by Load / Grain
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<br>No.-Powder-Lod grns-Vel FPS- FPS/ Grain-Pres CUP-CUP/ Grain
<br>1---RX22-----60.8-------2780---45.7---48,400--------796.0
<br>
<br>2---H-4831--60---------2840----47.3---50,000------- 833.3
<br>
<br>3---AA3100--59---------2649----44.8---48,300--------818.6
<br>
<br>4--IMR4831-58.4-------2788----47.7----48,700-------833.9
<br>
<br>5-RX19-------58.3-------2698---46.2-----48,800------837.0
<br>
<br>6-IMR4350--56----------2810---50.1-----50,000------ 892.8
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<br>7-760--------52----------2801----53.8----49,900-------959.6
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<br>8-IMR4064--49----------2710----55.3----47,200-------963.2
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<br>9-748--------48----------2632-----54.8---49,600-----1033.3
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<br>10-IMR4895-47.5-------2659-----55.9---48,000-------857.4
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<br>11-AA2520--47.3-------2572------54.3---49,500------910.3
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<br>12-IMR4320-46.3-------2584----- 55.8---49,900------894.1
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<br>13-IMR3031-46---------2688-------58.4---48,000-----821.4
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<br>14-H335-----45----------2583-------57.4--50,000------871.0
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<br>First by Velocity / Grain
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<br>1-IMR3031---46---2688---58.4---48,000---821.4
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<br>2-H335-------45---2583---57.4----50,000---871.0
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<br>3-IMR4895---47.5-2659--55.9----48,000---857.4
<br>
<br>4-IMR4320---46.3-2584--55.8-----49,900---894.1
<br>
<br>5-IMR4064---49-2710-----55.3----47,200---963.2
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<br>6-748---------48-2632------54.8---49,600--1033.3
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<br>7-AA2520---47.3-2572-----54.3---49,500----910.3
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<br>8-760--------52---2801-----53.8---49,900----959.6
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<br>9-IMR4350-56---2810------50.1---50,000----892.8
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<br>10-H-4831-60---2840------47.3---50,000-----833.3
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<br>11-IMR4831-58.4-2788----47.7---48,700-----833.9
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<br>12-RX19-----58.3-2698-----46.2---48,800-----837.0
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<br>13-RX22-----60.8-2780-----45.7---48,400-----796.0
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<br>14-AA3100--59---2649-----44.8----48,300-----818.6
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<br>First by Pressure CUP / Grain
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<br>1-748-------48----2632------54.8----49,600---1033.3
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<br>2-IMR4064-49----2710------55.3----47,200----963.2
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<br>3-760-------52----2801------53.8-----49,900----959.6
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<br>4-AA2520--47.3--2572------54.3-----49,500----910.3
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<br>5-IMR4320-46.3--2584------55.8---- 49,900----894.1
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<br>6-IMR4350-56----2810-------50.1-----50,000---892.8
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<br>7-H335-----45----2583--------57.4----50,000---871.0
<br>
<br>8-IMR4895-47.5-2659--------55.9----48,000---857.4
<br>
<br>9-RX19------58.3-2698-------46.2-----48,800---837.0
<br>
<br>10-IMR4831-58.4-2788------47.7-----48,700---833.9
<br>
<br>11-H-4831---60---2840------47.3------50,000--833.3
<br>
<br>12-IMR3031-46---2688------58.4------48,000--821.4
<br>
<br>13-AA3100--59---2649-------44.8------48,300--818.6
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<br>14-RX22----60.8--2780-------45.7------48,400--796.0

Bill, you're trying to play the game without using all the cards in the deck and substituting some other kinds of cards.
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<br>First, there's no "Howell theory." What I've been trying to explain is what I've been privileged to learn (from the giants on whose shoulders I stand to just "look tall") about certain discovered and demonstrated truths of interior ballistics. I despise this appearance of one-upmanship, but the fact is that Fact B is often not learnable, let alone understandable, without acceptance of Fact A and the discarding (at least methodologically) of Myth A or some Fact A from another field that doesn't apply to the question or problem under scrutiny. The inability to understand doesn't mean that what you don't understand is wrong, illogical, or mere theory.
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<br>Second, you're trying to reason by analogy -- not the guaranteed way to a sound conclusion, especially in a case like this where the analogies used as premises aren't exact parallels to the situation under scrutiny.
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<br>Third, temperature is lower when pressure is lower, so even though a larger charge produces more heat, that greater amount of heat (more Btu) isn't as hot (fewer �F) at the lower pressure, so the larger charge doesN'T erode the barrel as fast as a smaller charge that produces a higher pressure.
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<br>You're right about one thing -- I can't decipher those acres of gibberish numbers.

Bill, if I weren't certain that you'd want to know these next two very minor points, I wouldn't mention 'em. (Thought long and hard about posting 'em as it is).
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<br>"less grains" should be "fewer grains." Things counted in plurals (numbers, not quantities) take "few" and "fewer" -- fewer people, fewer cartridges, fewer gallons (but less gas). A parallel distinction, BTW, differentiates between "amount" and "number" -- a number of people or issues but an amount of food or influence, for example This can be confusing when they overlap, but most speakers of English "get" the real distinction between "I've given a great amount of thought to the problem" and "I have a number of thoughts about the problem."
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<br>"Velocitygrain" should be "velocity per grain," "ft/sec/gr," or "fps/grain." "@" means "at," not "per" or "each." The standard punctuation symbol for "per" or "each" is the virgule ("/").
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<br>Of course I knew at sight what you meant by each of the above. But as I said, I figure you'd want to know. You don't strike me as the sort who insists on intentionally perpetuating personal errors, no matter how insignificant they may truly be.
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<br>Miscellaneous Rambling - While at the range yesterday, I was contemplating our other discussion regarding burning efficiencies. I find interior ballistics interesting conversation material. But as Ken stated, few hand loaders are concerned with what happens to a bullet from the time the firing pin strikes, to the time the bullet leaves the muzzle. As long as you are following basic loading information, interior ballistics plays very little importance on exterior ballistics. Interior ballistics is only important to those in the powder manufacturing business and to a lesser extent, those of us who play with wildcat designs.
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<br>As long as the bullet leaves the muzzle at a reasonable velocity for the caliber, interior ballistics has done its job for 95% of the shooters/hunters out there. Just considering the complexities and variables associates with the two sciences (interior VS exterior ballistics), exterior ballistics is far more challenging and far more important to everyone who shoots.
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<br>Ken illustrated the five basic laws of interior ballistics in a few short sentences. However, mastering exterior ballistics can take many years of study and field experience. I have been reloading for 25+ years. When I began reloading, I took me a few weeks to understand the laws and importance of interior ballistics. In 25+ years of shooting, I am still mastering the laws of exterior ballistics - on some days I feel I still have a long way to go.
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<br>In summation - I think most shooters are lazy learners. Ballistics can be as easy as loading your gun with factory ammo and yanking the trigger OR is can be as complex as you wish to make it. My curious mind pushes me towards the complexities of shooting. The more I understand what is happening to the bullet every nanosecond helps me to become a better shooter. I feel fortunate to find other folks on the same quest...
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Ken:
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<br>I went back to my post and took a peek. It looks OK to me!!!!!! ( Smiley Face ). Dont' see them thar things you're talkin about!!!
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<br>As you know, out west, someone who isn't playing all of the cards, or dealing off the bottom of the deck, or putting cards up his sleeve, can get himself hanged!
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<br>The references to implication by association were certainly not designed, nor intended, to replace, supplant or attenuate, any scientific facts or postulations - at all. However, I do want to recount one important influencing incident to illustrate a point about the validity of coming to conclusions by observation ( if not scientific principle ).
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<br>In Sweden the SAAB Military Jet Airplane manufacturers ran into a serious design flaw with a new prototype jet fighter. The wings would tear off. After losing some aircraft and many millions of Krona ( dollars ) and exhausting all engineering resources ( ideas ), in desperation, management put up a suggestion box accessible to all employees with the plea that all suggestions were earnestly desired and would receive consideration.
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<br>In due course they opened the box and came upon one suggestion that said; " Put a series of perforations ( holes ) along the base of the wings where they join the fuselage. After much agonizing everyone agreed that they had tried everything else and had nothing to lose. So they built a prototype with a series of holes along the wind/fuselage junction and flew it. Perfect!!! Problem solved.
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<br>They then asked the person who had made the suggestion to come forward and be congratulated and rewarded. The janitor identified himself as the author much to the absolute dismay and astonishment of the staff. They couldn't contain their desire to know how the engineering staff couldn't solve the problem but a "janitor" knew the solution!!! The janitor said: " well, when I changed rolls of toilet paper in the restrooms I noticed that the paper - NEVER TEARS ON THE PERFORATIONS.
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<br>I spent some time attempting, laboriously, to "spread out" the tables of powder performance to make them more understandable. In the first table:
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<br>No. = number of load. ( 1,2,3,4, etc. )
<br>Powder = type of powder uses ( RX22, etc )
<br>Load Grains = the amount of powder loaded in the case, in grains
<br>Velocity FPS = muzzle velocity
<br>FPS/grain = the muzzle velocity divided by the load grains
<br>Pres CUP = the pressure expressed in copper units
<br>CUP/grain = CUP divided by load grains.
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<br>Table #1. "First by load grains":
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<br>First ( #1 ) in volume was RX22 taking 60.8 grains. Last was H335 at 45 grains.
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<br>Table #2. "First by velocity/grain".
<br>
<br>First ( #1 ) in velocity was IMR3031 which yielded 58.4 PFS per grain. Last ( #14 ) was AA3100 which gave only 44.8 FPS per grain.
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<br>Table #3. "First by pressure CUP/grain".
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<br>First ( #1 ) in pressure was IMR3031 which caused 1,033.3 CUP per grain. Last ( #14 ) was RX22 which produced 796 CUP per grain.
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<br>Note how each powder in a given table does not hold it's relative position in another table. For example RX22 ranks highest in powder requirement ( 60.8 grains in table #1. ) It ranks 13th in table #2 for velocity per grain ( 45.7 FPS ). And in Table #3 It ranks 14th in pressure per grain at 796 CUP per grain. It is not the best example. Other powders change their rankings in each table even more.
<br>
<br>Load Study 30-06 Springfield
<br>180 Grain Jacketed boattail bullet
<br>
<br>First by Load Grain
<br>
<br>No.-Powder-Lod grns-Vel FPS- FPS/ Grain-Pres CUP-CUP/ Grain
<br>1---RX22-----60.8-------2780---45.7---48,400--------796.0
<br>
<br>2---H-4831--60---------2840----47.3---50,000------- 833.3
<br>
<br>3---AA3100--59---------2649----44.8---48,300--------818.6
<br>
<br>4--IMR4831-58.4-------2788----47.7----48,700-------833.9
<br>
<br>5-RX19-------58.3-------2698---46.2-----48,800------837.0
<br>
<br>6-IMR4350--56----------2810---50.1-----50,000------ 892.8
<br>
<br>7-760--------52----------2801----53.8----49,900-------959.6
<br>
<br>8-IMR4064--49----------2710----55.3----47,200-------963.2
<br>
<br>9-748--------48----------2632-----54.8---49,600-----1033.3
<br>
<br>10-IMR4895-47.5-------2659-----55.9---48,000-------857.4
<br>
<br>11-AA2520--47.3-------2572------54.3---49,500------910.3
<br>
<br>12-IMR4320-46.3-------2584----- 55.8---49,900------894.1
<br>
<br>13-IMR3031-46---------2688-------58.4---48,000-----821.4
<br>
<br>14-H335-----45----------2583-------57.4--50,000------871.0
<br>
<br>First by Velocity / Grain
<br>
<br>1-IMR3031---46---2688---58.4---48,000---821.4
<br>
<br>2-H335-------45---2583---57.4----50,000---871.0
<br>
<br>3-IMR4895---47.5-2659--55.9----48,000---857.4
<br>
<br>4-IMR4320---46.3-2584--55.8-----49,900---894.1
<br>
<br>5-IMR4064---49-2710-----55.3----47,200---963.2
<br>
<br>6-748---------48-2632------54.8---49,600--1033.3
<br>
<br>7-AA2520---47.3-2572-----54.3---49,500----910.3
<br>
<br>8-760--------52---2801-----53.8---49,900----959.6
<br>
<br>9-IMR4350-56---2810------50.1---50,000----892.8
<br>
<br>10-H-4831-60---2840------47.3---50,000-----833.3
<br>
<br>11-IMR4831-58.4-2788----47.7---48,700-----833.9
<br>
<br>
<br>12-RX19-----58.3-2698-----46.2---48,800-----837.0
<br>
<br>13-RX22-----60.8-2780-----45.7---48,400-----796.0
<br>
<br>14-AA3100--59---2649-----44.8----48,300-----818.6
<br>
<br>First by Pressure CUP / Grain
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<br>1-748-------48----2632------54.8----49,600---1033.3
<br>
<br>2-IMR4064-49----2710------55.3----47,200----963.2
<br>
<br>3-760-------52----2801------53.8-----49,900----959.6
<br>
<br>4-AA2520--47.3--2572------54.3-----49,500----910.3
<br>
<br>5-IMR4320-46.3--2584------55.8---- 49,900----894.1
<br>
<br>6-IMR4350-56----2810-------50.1-----50,000---892.8
<br>
<br>7-H335-----45----2583--------57.4----50,000---871.0
<br>
<br>8-IMR4895-47.5-2659--------55.9----48,000---857.4
<br>
<br>9-RX19------58.3-2698-------46.2-----48,800---837.0
<br>
<br>10-IMR4831-58.4-2788------47.7-----48,700---833.9
<br>
<br>11-H-4831---60---2840------47.3------50,000--833.3
<br>
<br>12-IMR3031-46---2688------58.4------48,000--821.4
<br>
<br>13-AA3100--59---2649-------44.8------48,300--818.6
<br>
<br>14-RX22----60.8--2780-------45.7------48,400--796.0
<br>
<br>
<br>If you want to use the greatest amount of powder it will be RX22. The least will be H335.
<br>
<br>If you want to attain the highest velocity per grain it will be IMR3031. The least will be AA3100.
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<br>If you want the highest pressure in CUP per grain use 748. The least will be RX22.
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<br>These are the performance values that I was referring to. As it can be seen there is a vast difference in the amount of powder that can be used. In table #1, The spread is ( 60.8 - 45 ) = 15.8 grains. In table #2 the spread is ( 58.4 - 44.8 ) = 13.6 FPS. In table #3 the spread is ( 1033.3 - 796 ) = 240 CUP.
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<br>What I had suggested was to select the Howell design cartridges and then further attempt to improve upon performance by selectively choosing the various powders based on their performance characteristics.
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<br>If you want more residual case volume choose the powder that takes up the least space. *( long bullets or compressed loads ).
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<br>It you want more velocity try the top velocity producer.
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<br>If you want more pressure use the top pressure producer. If you want less pressure use the lesser.
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<br>If you want less recoil use the powder that produced best with the least quantity.
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<br>In view of these variations in powders, the generic term "powder" isn't descriptive enough.
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<br>Much more analysis and testing remains to be done.
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