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Old November 20, 2007, 03:55 PM   #1
joe poteat
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same powder different bullets

Whats wrong with using same powder for different weight bullets (125.130.150 and 165 grn) starting low charge and working up until you have an accurate load staying below max charge. I am talking 30-06 and reloder 7 and bench rest primers.
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Old November 20, 2007, 04:30 PM   #2
Shoney
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Although it is possible to use the RL7, you may be getting into very high pressure with a 165 and the benchrest primer. I would suggest RL15 over the RL7.
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Old November 20, 2007, 04:35 PM   #3
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Newton's third law. For every action there is an equal and opposite reaction. A light bullet has too little inertia to offer good acceleration resistance. As a result, a slow powder doesn't burn fast enough to keep up with it as it goes down the bore. The powder never gets to a pressure that burns it as well as good ballistic efficiency requires. The result is a lot of unburned powder going out at the muzzle and bullet that isn't moving at near its potential velocity. A faster powder therefore has to be employed.

In the reverse situation, a powder that burns fast will push the light bullet fine, but the heavier bullet will offer so much inertial acceleration resistance that pressure rises and it burns too quickly. That means it is burnt up before the bullet goes very far, and that means you have to reduce the quantity you use to keep the peak chamber pressure from getting too high. As a result, there isn't enough powder to push the heavier bullet to its velocity potential. Only going to a slower powder that lets the heavy bullet get going while it is still burning and then keeps burning and generating gas while the bullet goes down the bore, is going to accomplish that.

There is also the phenomenon of secondary pressure spikes to worry about. This is when a slow powder and light bullet are used. The initial move of the bullet from the caseneck generates enough pressure to get it onto the rifling and scooting down the tube. It apparently can scoot so fast that it actually gets ahead of the evolving gas and drops the chamber pressure. It then slows down and the inertial forward flow of powder particles catch up, slam into it and detonate. Texas gunsmith Charlie Sisk has been able to do this repeatedly, blowing up gun muzzles pretty much on demand. For light bullets, avoid slow powders. Reloader 10X is designed specifically for light bullets and unless you are using squib loads is about a slow as you want to go the a powder for them.
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Old November 20, 2007, 05:31 PM   #4
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IMR 4350 or IMR4831 are the powders you are looking for.
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Old November 21, 2007, 01:46 PM   #5
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Hate to disagree, but I think those are too slow to be safe for the lightest bullets. The secondary pressure spike hazard becomes a real concern.

You can see the measured secondary pressure spikes repeated through several rounds of .223 firing a 40 grain bullet with AA2320 in the last illustration at the bottom of this page. The load combination appears in loading manuals. In this instance the spike is not above proof pressures, so it won't likely burst the gun, even if it adds wear. Spikes in other combinations have, however, been measured that exceed 120,000 PSI in some instances. That's what gets into muzzle bursting territory.

At 125 grains in .30 caliber, I would look at IMR3031. Its better burning efficiency will add a couple hundred fps to what you can get out of two slower powders, anyway. 4831 and 4350 run ballistic efficiencies of around 23% with that bullet. 3031 gets to 29% BE in a full load, which is what Hatcher liked for the .30-06.
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