Wednesday, September 20, 2006

Gas Checks - Revisited

Flintlock Tom asks in comments:
Paw Paw, Help a noobie out: what is a "gas check", how is it done and what does it look like if done properly?
I anticipate doing some reloading after I retire but know nothing about the process.

Sure, Tom. I sometimes forget that folks don't know this stuff.

For lead alloy rifle bullets driven over 1500 fps, we seat gas checks on the base of the bullet to help with a pressure phenomenon known as "gas cutting". When the high pressure gasses slip past the bullet before it fully obturates in the bore, those gasses cut the base of the bullet. This blows molten metal forward of the bullet and coats the bore with lead, which the speeding bullet then irons onto the bore. This is one source of a leaded barrel. Other sources of barrel leading include improperly fitted bullets, improper bullet alloy, insufficient bullet lubrication and improper lubricant type.

Leaded barrels are bad, in that accuracy suffers and lead is hard to clean out of a barrel. So we use gas checks to reduce or eliminate leading the barrel.

A gas check is nothing more than a cup of gilding metal, manufactured by the Hornady company. They are sold in bags of 1000.

Here is a picture of some gas checks laying on my bench, with a penny for scale.

These little cups of gilding metal are seated on the base of the bullet during the sizing operation. That same operation crimps them into place. The bullet is then lubricated with an appopriate bullet lube, such as the NRA Alox/beeswax lube.

Properly seated gas checks on lead bullets look like this.

Those checks are properly seated on the base of the Lyman 311041 bullet that I use in my .30-30 loads. After lubrication they will be ready for loading. These bullets can be driven to 1800 fps with no danger of barrel leading and are the cat's whiskers for North Louisiana brushy woods deer and hog hunting.


Flintlock Tom said...

Thanks for accomodating me. I have a lot to learn but the prospect of fine-tuning a load for a peticular firearm is an exciting challenge.
I'll look forward to reading all your reports as the process proceeds.

Thanks again

ben said...

Dang think even I understood that