Correct sizing of Cast Boolits

[Carolina Cast Bullets]

I have run into a puzzling question.

How much over slugged bore should a cast bullet be used? Would using a bullet sized .379 in a bore .376 cause problems?

If so, what kind of problems? First thing that comes to mind is higher than usual pressure but would this be excessive?

I hesitate to comment because I have always read and considered nothing more than .002" oversize as "normal"

What say the members?

Jerry
Carolina Cast Bullets

[old turtle]

I do not think it would increase pressure to any great extent. I shot .311 in .308 barrels in the old days with no problems. I might hurt accuracy a little but who knows. I like to use .001 over bore. I checked, and Lyman makes a .377 sizing die. But you might try it at .379 and see what happens as to accuracy. It may be just fine. I assume that you are talking cast boolits and not jacketed which might be a problem.

[MT Chambers]

The biggest problem that I've had with oversized bullets is that once loaded, the case expands to fit the bullet and then won't chamber properly.

[largom]

I seat an unsized boolit in a case and if it chambers easily I go with it unsized. Using Felix World Famous Lube I shoot .312 dia. boolits in my 30 cal. guns at 2000fps. without any problems. I only size my boolits when necessary. I lube the boolits in an oversized die.

Larry

[Centaur 1]

Try sizing a jacketed bullet just .001" through a Lee sizing die and see how hard it is. One you might have on hand is a .357" diameter bullet and a .356" die. I can push a boolit that cast .360" through the sizing die with a lot less effort than a .357" jacketed bullet. Like MT stated, you'll run into chambering issues first.

[williamwaco]

The biggest problem that I've had with oversized bullets is that once loaded, the case expands to fit the bullet and then won't chamber properly.


Excellent Answer.

This is the problem with attempting to load bullets "as cast".

About two in ten will not chamber.

Aside from that, I don't think it makes much difference. I have fired .360 bullets in .357 and 9mm handguns that slug .356. I have to carefully select cases with thin necks to make it work.

The .357 mags spray lead from the cylinder gap ( the throats are .3565 ) but shoot accurately and do not lead the barrel.

The 9mms produce no noticible effects at all.

I had intentions to try the same experiment with "as cast" Lee TL bullets measuring .361 but could not find enough .38 Special cases that would chamber to make a meaningful test. I just didn't try with the 9mm.

Note that I am not saying the Lee mold routinely drops bullets that large. It doesn't. It averages .359 to.360. But a few are larger.

To the original question.

My .38-55 Slugs 0.376.
The throat diameter is .396.
A cartridge with a throat diameter of
.395 chambers easily. ( Drop-in)
.396 is a No-go. Can't close the action.
.3955 is very snug but only finger pressure is needed.

Neck diameter of cases varies from .08 to .095. Using 0.09 as an average. The largest bullet that will chamber is 0.377 and that is the size I use. Actual average diameter is .03772. (Lyman Die)

I culled out all the thick neck cases and didn't use them until I got a Forster outside neck turner. Then I neck turned all the thick cases and 40 of the normal cases to a neck thickness of 0.085. I did not cull the thin ones.

What happened you ask?

I gained about 45 good cases from the formerly too thick ones.

In shooting 12 three shot groups with the most uniform cases, after turning. I can detect no difference in accuracy, but, the point of impact moved about an inch North West.

SO:

If you can chamber it, I would not be afraid to shoot it. Odds are, you will not be able to close the action on a bullet that large.

[badbob454]

Excellent Answer.


If you can chamber it, I would not be afraid to shoot it. Odds are, you will not be able to close the action on a bullet that large.

( if of the same case cartridge ) just to clarify for new reloaders