actual boolit dia. vs. load data dia.

[ksJoe]

I'm thumbing through "The Complete Reloading Manual for the 45-70 Government" and I have an unanswered question.

The recipes that I've noticed specifying a diameter give .458. I've read several suggestions that current Marlin 1895's like .459-.461. My Lee 405 HB is dropping WW boolits at .460-.461. So I'm planning on using them as cast.

But logically, it would seem that a tighter boolit will raise the pressure. So, I'm wondering if I should care that it is several thousandths over the recipe.

I'm guessing the load data for lead in this gun maxes out based on barrel leading and the max velocity you can push a lead boolit, because the data for jacketed is often twice the pressure.

So I figure if the larger boolit raises the pressure in my 1895SBL, it won't do it enough to hurt the gun. Right?

What about a trap door? Those loads are pressure limited, so would going from a .458 to a .460 be dangerous?

[btroj]

Pressure will go up, if the bore is .458. I would assume that a .460 bullet in a .460 bore is no different than a .458 bullet in a .458 bore.
Lead alloys are also pretty soft compared to a jacketed bullet. The extra size will make a tiny different in pressure.

In the end, cast the size your gun needs and all is good. Use the recipes as found with complete confidence.

[MtGun44]

Yep.

Bill

[Larry Gibson]

The correct answer is no, psi will more than like not increase at all.

Consider this; we size our cast bullets all the time. Unless we are useing a very, very hard alloy and sizing more than .004" it really doesn't take much "pressure" to size them does it? Now that same bullet at .462 and fired in a .458 barrel will get sized at a quite low psi to .458 within the 1st bearing length of travel in the throat/bore. After that the bullet is .458 and acts, pressure wise, just like any other .458 bullet. This is very early in the time pressure curve well before the maximum pressure is reached. Any difference in psi will be within the normal ES of the ammuntion (even loads with fast burning powders) and will be very difficult to discern. Bottom line is that with cast bullets it is a myth that a reasonbly oversize cast bullet will raise psi, it does not.

I have attempted to determine a psi increases with numerous cartrdges from the 30-30 up through the 45-70 by measuring the psi's with normal and oversized cast bullets. I have tested many strings of .462 - .464 sized bullet in my Siamese Mauser 45-70 and can not find and increase in psi at all given the same load with .458/.459 sized bullets.

Just last week I ran 65 rounds of various cast loads through my .44 mag Contender. The bore was fouled but not leaded to any extent. I then fired a 10 shot test string of Magtech 240 JSPs. The old myth/wives tale is that psi's are also going to higher with that, right? Well the 1st two shots were below the string average in fps and correspondingly lower in psi also. I have been running tests like this for years with the chronograph measuring velocities and the last 3 years measuring the psi. Most often the 1st few shots are well within the expected range of velocity and psi for that ammo. Another myth busted.

Larry Gibson

[ksJoe]

Now that same bullet at .462 and fired in a .458 barrel will get sized at a quite low psi to .458 within the 1st bearing length of travel in the throat/bore. ... This is very early in the time pressure curve well before the maximum pressure is reached.

That makes sense. That's what I was missing.

Thanks!

-Joe

[44man]

The only problems I have found with 45-70's is the vast difference in bore dimensions. Never go by load manual boolit diameter suggestions. You need to know your groove diameter in your gun.
Over size is good but if you buy a Lyman mold and it drops .457" and your bore is .460" you might as well throw the boolits! :mrgreen:

[MtGun44]

I submit that it WILL require more pressure to size the oversized boolit down, laws of physics
will be strictly enforced. You are deforming a greater volume of metal and this absolutely
will require extra energy input for it to happen. Has to.

HOWEVER, it will be such a small amount as to be totally inconsequential in any meaningful
sense.

Bill