Gas Checks too large?

[TG70]

A question from a newbie. After splitting one case and wrinkling a few seating cast boolits (38 special) I measured the boolits and checks. The gas checks measured .359" diameter, the boolits a bit over .358" (I don't know if the sizer that we used was .358 or .357). The problem did not occur with most of the cases, but the cases are a mixed lot of different manufacturers and uncertain provenance. I think that I can probably expand the cases a bit more before seating the boolits, but...

Is this a normal situation with gas checks?

Should I not use the boolits?

After measuring the 38 boolits I decided to measure some .308 boolits that were sized to .309; I found the gas checks to be .310, the boolits a bit over .309. From reading on these forums I am not surprised to find that the sized boolits are not precisely .309 but I am not sure what to make of the .310 checks.

Tom

[Larry Gibson]

It is normal for the GC to be slightly larger than the cast bullet after sizing. Brass has more "springback" than lead or lead alloys.

Your problem with the .38 Special cases may be one of an insuficient size expander and/or not belling the case mouth enough.

Larry Gibson

[runfiverun]

if you really need those g/c's to stay the same size as sized you need to anneal them.
now if yyo are using 5 different kinds and ages of brass are you really surprised some of them are giving you trouble?
different lengths of brass will cause you as many problems as thicker or thinner brass.

[TG70]

thank you for the replies.

It sounds like the gas checks being a bit large is more or less normal. Expanding the cases a bit more seems to have solved the case accordion problem.

I'm shooting for minute-of-milk-jug with light loads so not very concerned with well matched brass. I did check the cases I used for maximum length.

I fired 50 or 60 of the gas checked boolits Saturday - no apparent problems.

Tom

[XBT]

To expand a bit on what was said above; the gas check being slightly larger than the boolit is normal. Your mixed brass is of slightly different lengths, which is causing the problem. Some of the shorter brass is not being expanded or “belled” enough at the mouth to allow the correct starting of the boolit. Brass that is of slightly different lengths will also cause some variations in the roll crimp usually used on revolver ammo.

All this does not matter much unless you are trying for maximum accuracy. Just set the dies to expand the shorter cases correctly and you should get good results.

[Calamity Jake]

Why are you using a GC in the 38 anyway? You can't push them fast enough to need one.

Slug your cylinder throats and bore, cast boolets out of WW or softer and size to .001-.002 over bore dia. if throat dia. will let you.

You can shoot a GC designed boolet with out the check with no problems.

[TG70]

Thanks for the additional replies.

Expanding the cases a tad more seems to have taken care of the seating problem.

I understand about not needing the gas checks. Why did I use them? Because they were there, and I wanted to shoot my 38. My first, and only, time casting I used a friend's equipment. We cast using half a dozen different molds. Can't recall why we used the GC mold for 38/357 or thinking about whether or not to put the checks on. Possibly my friend wanted to see how well the mold cast or may have figured that I would use them in my Marlin.

Tom

[docone31]

That mold is probably more suited for the .35 Remington. Hence the gas check.
I found, with mine, .357 jacketeds shot real well. I favoured the .180gn sillywet bullet.
It was my sweet spot in my XP-100.