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 Bullet weight effect on powder charge

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rsrocket1



Male Number of posts : 13
Age : 59
Location : Sacramento, CA
Registration date : 2013-10-28

PostSubject: Bullet weight effect on powder charge   December 6th 2013, 10:09 am

I started this quest to see if Alliant Black MZ can be shot with any sort of consistent velocity.  I love Blackhorn 209 and can reliably and accurately shoot with it, but if I can shoot Black MZ at less than 1/2 the cost ($23/pound vs $32/10oz), I'd like to use it.

I've developed a workable method of measuring and loading Black MZ to where a 10 shot string gave me a 63 fps extreme spread and 18 fps std dev.  Good enough.

This was with 230g cast lead 45ACP bullets in T/C sabots.  I was then asked to chrony some .50 cal paper patched bullets by a fellow.  It turns out these bullets are 550 grain bullets and with the patch, they weigh between 580 and 590 grains!

So the question is, with BP and BP substitutes, if you double or triple the bullet weight, what effect does that have on the peak pressure of the same load of powder?

I know that with smokeless powder, doubling the weight of the bullet can more than double the peak pressure but smokeless powder burns into a gas almost immediately so it is very sensitive to the confined volume.  

Does BP or a BP sub like BH209 or BlackMZ burn so slowly that a heavier bullet doesn't affect the peak pressure very much?  I've emailed Alliant and CVA, but no response yet.  
I might not mind the super heavy recoil of such a load, but I don't want to blow up my gun.

Thanks.
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Spitfire



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PostSubject: Re: Bullet weight effect on powder charge   December 6th 2013, 10:34 am

With a bullet that heavy back down on your load . The long range crowd push 530 -600 gr PP bullets with 90 -100gr 2F Wano or 1.5F Swiss in a .450 bore rifle.
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patocazador
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Registration date : 2012-08-22

PostSubject: Re: Bullet weight effect on powder charge   December 6th 2013, 10:38 am

Intuition tells me that a 580 grain bullet is much longer and, of course, more massive than the usual ~350 gr. .50 caliber bullets. Starting that heavy bullet will take longer and moving it will be more of a task for the powder load. Also, because of the additional length, the bullet will take longer to exit the muzzle .. like shooting a cucumber compared to an apple, long vs. round. All of this will create more backpressure which will have a tendency to put a lot of strain on the barrel and the breech plug. It may also blow the nipple out. You will get blow-back most likely and, if your gun has a flaw, it may rupture at the weak point.

Reduce the load by 30-40% and work up a small amount at a time. When your velocity peaks and your groups open up, back off a little and use that as your load.

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Clyde



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PostSubject: Re: Bullet weight effect on powder charge   December 6th 2013, 11:25 am

I've shot about 3 lbs of BlackMZ .  If you want consistency then your going to have to do two things turn the jar over and gently shake it a few times to move the really fine grains off the bottom and then weigh your charges Jon has a a scale for APP powder on the propellant page its pretty close to Black MZ.  I got three deer this year with a sidelock and 80 gr over 300 gr PR Bullet Kieth Nose the load stayed consistent all fall .

As far as the pressure the heavier the bullet the more pressure you will get .  What type of ml are you shooting this from?  If its CVA you may void the warranty if you shoot 150 gr of powder and use a bullet over 300 grs. in some of their rifles.
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rsrocket1



Male Number of posts : 13
Age : 59
Location : Sacramento, CA
Registration date : 2013-10-28

PostSubject: Re: Bullet weight effect on powder charge   December 6th 2013, 3:21 pm

Thanks for the replies so far.
The gun is a 2004 CVA Optima Pro.  I have no intentions of going over any recommended limits and doubt that I will want to go over 100 grains with such a heavy bullet.  For my own use, I always start low and stop when I find an accuracy node and use the minimum load that "gets the job done".  

If a heavier bullet generates higher pressures as it does with smokeless, then such a heavy payload ought to result in more consistent combustion with lighter charges than with light bullets.  I'll probably start with 70g (by volume, 62g by weight) and see if I get a decent group then maybe work up slowly to 80 or 90g and stay there.
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