Cast Bullet Velocity Parameters

giterdone
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Joined: Thu Feb 07, 2008 7:36 am

Cast Bullet Velocity Parameters

Postby giterdone » Thu Feb 07, 2008 8:17 am

Dan... My cast bullet experience has been with Long Range BPCR rifle competetion. I used 20-1 alloy with a .060 wad under the bullet and never looked back. Now I find myself shooting rifles with cast bullets, using smokeless powder and with different (harder) alloys. From articles and books I have gathered bits and pieces of info on velocity vs. alloy and need your input to clear things up. One book says keep the velocity under 1600fps (w/smokeless) for the best accuracy (w/o gas check) but it does not say to use a wad (veg. fiber or LDPE) under the bullet to protect the base (which is what I used w/black powder). Another says you can load cast bullets up to 2400fps w/o a gas check (using Lyman #2); another says use a gas check for high velocity. Will a fiber wad or LDPE wad protect the base of a cast bullet at higher velocities (1800-1900fps)? Most of my "Hard Cast" commercial bullets are in the 15bhn range, I have some of my wheelweight alloy that I heat treated that are 22bhn (after 2 weeks). What guidelines do you recommend for (Rifle velocities) hardness, accuracy and hunting? Should I use wads under my 15bhn bullets (plain base) at 1800-1900fps? Or should I just skip the plain base and only use gas check bullets?
:?

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mtngun
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Re: Cast Bullet Velocity Parameters

Postby mtngun » Thu Feb 07, 2008 3:31 pm

My experience with wads is limited to a few experiments with NECO wads under gas checked bullets. If I remember correctly, the wads didn't help things one iota, so I didn't pursue them further.

Gas checks make life far easier, even at lower velocities. Plain base rifle bullets are for someone who just likes to experiment, or someone who is determined to save money -- not a small consideration given the current price of gas checks.

So my suggestion is use a gas check, and save the plain bases for when you are bored and looking for a challenge.

BHN can go either way. Many standard cast rifle bullets are bore riding designs with undersize noses, not to mention undersize bodies. A soft bullet may obturate and make the bullet fit better, improving accuracy. Dave Scovill did a nice article on this subject once, testing different BHN's in a 30-30 with a bore riding nose. In his test, the softer bullets shot better because the undersize nose bumped up to fit the barrel (Dave never bothered to explain why the bullets didn't fit right to begin with).

Likewise with BPCR bullets, it is common for the nose to be undersize so it will chamber easily, and then the "bump" from the black powder obturates much of the nose to fit correctly. However, with smokeless powder and higher velocities, I've had better luck with hard bullets that fit right to begin with.

There is no simple answer to your question. Every gun is different. Mass produced guns are highly imperfect from the cast bullets point of view. Much of the cast bullet game consists of finding a bullet that compensates for the gun's imperfections.

For hunting, I use a hard (usually heat treated WW) bullet with a big meplat. This alloy will not mushroom, but it will usually "rivit" at rifle velocities, becoming close to a full wadcutter, and that is good enough with big bores.

jwp
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Re: Cast Bullet Velocity Parameters

Postby jwp » Sat Feb 09, 2008 11:36 pm

There's an interesting discussion of cast bullet hardness versus pressure in Richard Lee's "Modern Reloading - Second Edition". Among other things, he presents a systematic procedure for determining the maximum pressure that should be used with a given alloy hardness, and a way of approximating the pressure generated by a particular load. I can't vouch for the accuracy of Mr. Lee's data, but he certainly comes across as a person who is very interested in using carefully measured data and sound engineering reasoning as much as possible to replace the mythology, superstition, and dogma that is present in too many places in the cast bullet reloading universe. Not unlike our host here, actually.


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