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I have a question guys

This is my understanding.
On selecting cast bullets  for best accuracy one must be careful that the cast diamenter  is about .0005 to .0015 above the sizing diameter. the sizing die must be slightly less than the chamber diameter. and the chamber diameter will be larger than the groove diameter. The bullet must be perfectly concentric and completely filled out.

When the revolver is fired the bullet is upset to fill the chamber which makes it oversized for the barrel. But not to worry. When this oversized bullet enters the forcing cone (which is seldom precisely aligned with the chamber) the bullet is swaged back down down to barrel groove diameter as it is forced  into the rifling. Under pressure the barrel expands slightly and the bullet grows at the chamber end of the barrel and then is swaged down before exiting. In other words that perfect cast bullet has been subjected to a severe beating and the size changed all over the map. What difference does it make if the bullet is not perfect to begin with if its dimensions are going to be changed two or three times before it exits the gun barrel?

Glenwood
 

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The Hog Whisperer (Administrator)
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Good point!  A cast bullet does get re-sized a bit on it's trip down the barrel, especially from revolvers.

So, let's restate the question another way:  Given that the bullet won't leave the barrel in exactly the same condition it left the cartridge case, what are the important attributes of the bullet that must be kept?

Let's start with the bullet base.  It needs to start out uniform and leave the barrel in a uniform state (minus the groves that the rifling will put into it).  If it is damaged on one side, the powder gases will tip the base as it leaves the bore, reducing downrange accuracy.

So that's the reason for holding the sizing tolerances just so.  When the bullet leaves the case, we don't want powder gases to escape past it, which would likely start to erode the edges of the base.  Therefore size so it will just fit in the throats.  It needs to be round, of course.

Then, if the throats are just a bit bigger than the rifling, the gas seal will hold when the bullet jumps into the barrel.  If the groove diameter of the rifling is larger than the cylinder throats, then it is unlikely that this gun will shoot cast bullets well, althought sometimes gas checks help a little.

Other attributes... weight.  A uniform weight, combined with a good gas seal and uniform powder charges, should help deliver a uniform velocity which will help downrange accuracy.  Non-uniform weights often indicate voids in the bullet's interior, which could throw the bullet out of balance and that's not good.

As far as the rest goes.... probably some things are not as critical as we'd imagine.  Bullet appearance kind of helps us judge what the casting temperature is and whether the bullet filled out OK, but isn't a critical indicator by itself.  The nose of the bullet is about the least critical part, assuming it's not severely damaged.

Hope this helps.
 

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As glenwood was saying about the non uniform weights. If you have voids in the bullet the spinning motion of the bullet in flight will cause the bullet to wobble. A .44 bullet traveling at 1650 fps will turn right around 59000 rpm. That is doing some spinning. Smaller calibers will spin faster than that as will faster bullets. You want your bullets to be as good as you can get them.
 

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Also setting the gun up to proper dimensions for cast bullets will keep those deformations to a minimum. I have always tryed to keep obturation to the minimum since it is most severe from the base of bullet forward, This is where a supreme lube comes into play for the friction control. ie (LBT BLUE) The more a cast bullet has to obturate to get sealed up the more deformation is going to play a role in accuracy. The better you keep the cast bullet to its original shape and size the better it will shoot, by using bhn to control the amount of obturation and a powder that will get it to the proper velocity while being as gentle as possible with the bullet. something else that can ruin a cast bullet before it is ever fired is simply loading it in the case. your sizing dies and bhn must be correct!! but thats another story itself.  you mentioned barrell to cylinder alignment as the bullet enters forcing cone? this is a crucial area especially with short bullets. The bullet will be throwed to one side of rifling. center axis of bullet and center axis of bore are no longer a team and neither is accuracy, longer bullets will shoot better from a mis-aligned gun and one that has a tapered ogive (lbt-lfn). I Hope this has helped you some with the key point being bullet FIT. and another key is to keep the bullet in its unfired shape as close as possible till it exits the barrel.
Jim.
 

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I had a lyman 30cal mould that was out of round with the smallest measurment .306. This thing gave me groups of about 18 inches. I didn't realize what the problem was until the mould was out of warranty but Lyman replaced it anyway with a new one which cured the problem.
 
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