Please explain "gas check" to a beginner

[Thirties]

I will load for .38 spl revolvers), and 9x18 pistols. I am new to reloading, so please excuse this beginner's question. I did a search here for "gas check", but no references explain what it is, and when one would use or not use it.

My understanding is a gas check is a physical object, loaded at the base of a bullet, for the purpose of preventing hot gas (flame?) from melting the "skin" of a lead bullet on ignition. Is there a more complete description?

If that is what it is, my second question is when to use, or not to use a gas check? My third: which bullets are gas check designs (saw one reference to this in a message)?

For my .38 specials I plan on loading 148 grain hollow base wadcutters, and 158 grain flat base semi wadcutters, both commercially made (I'll not be home-casting my lead).

For my 9x18 Makarovs, I plan to load 96 grain flat base semi wadcutters (cast by makarov.com). I loaded some 9x18 LSWC for the first time yesterday, but did not use gas checks (don't have any).

Let me add that in my loadings of both calibers, I will be going for accuracy and less noise, not high speed.

When using a full metal jacket bullet (lead at bottom uncovered), are gas checks never used? And what about plated lead round nose bullets?

Thanks...

 

[Delmar]

Gas checks are nothing more than a copper cup installed at the base of the bullet which prevents the base of the lead bullet from melting due to heat. Think of it as kind of a bottle cap at the bullet's base.
If you are not loading your rounds faster than Mach 1-about 1088 feet per second and/or using pure lead projectiles, I doubt you are going to see much advantage to a gas check. It might be something you would want to experiment with, but its normal function keeps the barrel leading down in high speed loads.

 

[Thirties]

Delmar, thank you. That's what I thought it was. I guess I don't need them.

But if I did, are these things sold, or hand fashioned by the loader?

Should they be exact diameter of bullet? If so, when you crimp, would thay cut or weaken the case wall?

 

[Sisco]

Gas checks can only be put on bullets designed for their use. The bullet is moulded with a special base that allows the gas check to be installed and still retain the same diameter as the rest of the bullet.
They are most commonly found on cast rifle bullets or as Delmar pointed out, handgun bullets intended for high velocity.
One property of lead bullets that helps reduce barrel leading is their ability of the base to "obiturate" (sp?) when fired. Meaning the base actually expands somewhat sealing the hot gasses in behind the bullet while it travels down the barrel.
Sometimes if a bullets composition is to hard and obitration does not occur the hot gasses can leak past and heat up the lead causing barrel leading.

 

[Thirties]

Thanks Sisco. So I guess I won't be needing gas checks with my hollow base wadcutters, or my flat base semi wadcutters in either .38spl or 9x18 since I'm loading for low velocity, correct?

Great -- one less thing to think about . . .

 

[Sisco]

You are correct sir. Hollow base wadcutters are more or less designed that way so they will expand and seal at lower pressure (powder charge).
The only time I used gas checked bullets in a hand gun was .41 mag. Was able to push them faster than non-checked bullets with minimal leading.

 

[braindead0]

copper cup

or brass, at least the pile I've got here for .30-06 are brass.