Gas Check Question

[Erik]

Hello,

As some of you know, I am making 7.62x39 cast bullets for the first time. I am using the Lee 155 grain mold. Unfortunately, I can't get my gas checks to attach. Some people here suggested I just use .30 gas checks and run them through a .314 bullet sizing die and that the die would crimp the gas checks in place. However, doing this does not attach the gas checks at all.

What am I doing wrong?

[shotman]

Not staying on or not going on at all?

[dromia]

What size is your boolit dropping from the mould, what is the diameter of the gas check shank on the boolit?

Also what manufacturers gas checks are you using?

[Erik]

I'm making my own gas checks, using a Freechex II .30 and pieces of aluminum roof flashing. They slip over the mold quite easy and just barrrely stay on by themselves. However, the .314 sizer doesn't do anything to tighthen them down at all. If you bump the bullets, the gas checks just fall off.

The bullet mold is a Lee C312-155-2R.

[Calamity Jake]

The material you are using to make the GC is not thick enough, get material at least .003 thicker.

Or you can use a small drop of super glue.

One other thing, use some kind of lube when making the checks so the forming die does not thin the walls.

[Erik]

The problem was solved by moving to a .012 sheet metal. They sort of "snap" on now and seem to stay.

[PatMarlin]

Can you pull them off once sized? IN other words are they on solid after sizing that you can't pull off with your fingers or are they just kind on?

[Erik]

They can be pried off with the fingers, but it takes some effort. The sizing die still doesn't touch them.

[PatMarlin]

Part of the reason is the material, and part is the die design.

Those 2 I've learned interact closely, and aluminum is not the greatest and does not work as well as copper.

Your problem I would say is the die design more than the material though., The dimensions are critical, and how the check disk is cut and formed is critical. It's amazing how much so, and how it effects the way a check crimps and sets on a shank.

[Erik]

The FreeChex II creator is sending me a .280 punch. I think that will surely solve the problem for good.

[PatMarlin]

A .280 punched disk for a 30 cal check? no way.

[shotman]

Pat he said .280 punch Add thickness of materialx2
The coil stock that siding guys use is .015 around here Gutter material is .027

[PatMarlin]

You've got to be talking about a male forming die, not a punch.,

[Erik]

Yes, that's what I'm talking about.

[Larry Gibson]

Erik

I also make my own GC (.22, .30/.31 and 8mm). I'm not sure a smaller punch will help. I tried that as GCs made of .012 brass shim stock are a tight fit on oly about half of my .30 cal moulds when sized at .311. I found that for a tight fit after sizing the GC material thicknes has to be .002" thicker than twice the GC material thickness minus the diameter of the GC shank of the bullet.

I've shot a lot of the old style Lyman non-crimp GCs over the years (still have a few left of assorted calibers) and really never could tell if there was any difference in accuracy between them and the crimp ons. Attached photo is a test of the Hornady crimp on vs my own slip on made of .012" brass shim stock. The cartridge was 8x57 and the rifle is a very accurate Yugo M24/47. The load was nothing special other than a known good load for .325 cast bullets of 200-210 gr. The bullet in this case was the GB C325-190-FN. The load was 28 gr 4895 with a dacron filler in Turk cases with the original berdan primers.

The groups are 12 shots (2 foulers and 10 for group) shot at 100 yards from the bench. The barrel was cold and clean for each group. You can see the first two fouling shots went slightly high with each GC. This was not enough to negate the use of that load for hunting with a cold, clean barrel. For all intents and purposes the there is no accuracy difference.

The one real potential problem with the slip on GCs is if the GC is seated below the case neck. It is posible for the GC to come off in the case and cause problems. However with a dacron filler where the GC is slightly compressing the dacron negates this as the GC will then stay on the shank. Another plus for the dacron filler I guess. I've found a few tin cans to give appropriate thickness for GCs but have quit using aluminum beer/pop cans as they don't stay on very good at all and I'd just as soon not have to glue them on. I'm still looking for the Bud aluminum "bottles" but haven't found any so far.

Larry Gibson