Wednesday, November 12, 2014

Gas checks on non-gas-check bullets

While back I wrote about modifying plain-base cast bullets to take a gas check.  Few days ago Dad showed me another way he figured out, and that's what this is on.

For a little background:
A plain-base cast or swaged* bullet has a flat base with square corners.
The basic cast bullet, used by the Deity-only-knows-how-many millions over time(this particular one is a 158-grain semi-wadcutter hollowpoint from Hornady).  They have very definite limits as to how fast you can drive them because of that plain base: start pushing them too fast and the propellant gasses wind up eroding the base and corners a bit, which both screws with accuracy and causes lead fouling to build up in the rifling.

Solution: modify the mold a bit so the base has a heel or smaller-diameter section at the base and put a gas check on it.  Small copper cup fits over that heel, and when you run the bullet through the sizing die is crimps it on.  That check protects the base from the propellant gas, and(I think) will tend to scrape out any fouling as the bullet travels forward.  You can push  a gas-checked bullet a lot faster.

Now, before jacketed hollowpoints became truly reliable, one of the only bullets that could be counted on to upset(expand, mushroom, etc.) reliably was the semi-wadcutter hollowpoint, cast or swaged from a fairly soft alloy.  This was the FBI load for quite a while, and a number of other agencies wound up using it as well, in .38 Special +P or .357 Magnum loads.  Among others, Hornady sells these(see above). 

Hornady swages these with a knurled(textured) body and coated with a dry lube, others use standard lube grooves full of lube.  I'd fired some of the Hornady, and they shot well but I still got a bit of fouling, and that was below +P load levels.  So I screwed around and used a collet-type bullet puller to squeeze a heel on the base to take a gas check.  It works, but a bit fiddly to do.

Enter Dad.  I'd mentioned this to him, he picked up a box and thought on it a bit, wondering how to form a shank to take the check.  And did this:

That's a piece of .126" aluminum scrap he had laying around.  After a bit of measuring he drilled two 11/32"   holes in it, and lightly touched them with fine paper to clean off the burrs.  Take a bullet, set it squarely on a hole.

Push straight down with medium pressure and give a turn.  Examine. 

This one took a couple of turns to form the heel, though sometimes might take another turn. 

Press the gas check on
and run it through the sizer to crimp it on.

That's a hell of a lot simpler than the process I came up with.  Dad used his Lyman sizing press to seat the check, pushing the bullet just far enough down to crimp it on; I've got a Lee bullet sizing die in .358" and I think it'd work better as you don't have to worry about mashing the nose.

*Swaged: formed by forcing lead into a die to form the bullet


B said...

You can always try paper patching. I've driven a lead .357 SWC to 2100 FPS in a rifle with no leading.

I do pure lead in a 45-70 to 1800 paper patched with no issues either.

Firehand said...

Have tried it in the past, may have to again; still have some suitable paper.

What kind of rifle with the .357?

B said...

Rossi lever '92. 20"

I use standard lined notebook paper and size the lubed bullets after they dry. The only hard part is getting the dimensions right for each bullet type so that the wraps end up right. Once I get that right, then I make a template out of aluminum (or brass) to help me cut the paper.

(BTW, the load was, IIRC, 15.7 G H-110 for the .357. Safe in my revolvers, but the powder mostly burned outside the revolver barrel. (YMMV, Anyone reading this: use proper reloading precautions on this load, work up to it in a safe manner. You are responsible for your own work and safety... I take no responsibility for anything, etc.....)

B said...

I checked my notes.... 16.6 grains of h-110 was my max load before I started seeing primers back out and other pressure issues. (Again, use standard reloading cautions when working up to this load)

Chrono'd velocity was 2140 FPS