What is a gas check

Gas checks crimp onto the base of lead cast bullets to act as a gas seal,prevent the soft lead base from deforming when fired and prevent gas cutting,resulting in more consistant MV,accuracy etc.
 
they are copper cups that press over the base of cast bullets. The bullets have a smaller diameter base to accept the gas check. Think in terms of a copper base which comes up about 1/8" above the bottom of the slug.
Their use is to protect the base of the bullet because the base has a great deal of impact on the accuracy of the bullet (more than the nose). They also I think allow you to load to slightly higher velocities than lead base bullets. They also are considered to let the bullet grip the rifling more tightly and perhaps to reduce leading of the barrel.
Worth noting that they are not normally permitted in most black powder cartridge competitions

cheers mooncoon
 
They are attached to the back of a cast lead bullet, and stop gasses from escaping from behind the bullet.

Basically seal the bullet better as it goes through your barrel.

If your bullets are sized properly to your bore there isn't much of an issue, but when you are using hard cast generic bullets they may be sightly undersized which is an issue with leading, gas checks can help.

Also allows you to push the cast bullets a little faster without worrying about the above issues.
 
Thanks Guys, now I know.

They are attached to the back of a cast lead bullet, and stop gasses from escaping from behind the bullet.

Basically seal the bullet better as it goes through your barrel.

If your bullets are sized properly to your bore there isn't much of an issue, but when you are using hard cast generic bullets they may be sightly undersized which is an issue with leading, gas checks can help.

Also allows you to push the cast bullets a little faster without worrying about the above issues.
 
I use gas checks on some centrefire ammo, but not all. When they really come into play is when you are trying to load over 1800 or so feet per second.

The gas check potects the base of the bullet as the cartridge is fired, preventing the base of the bullet from being melted/vapourised and leaving all kinds of lead in your barrel, not even to mention exitng the bore in an unbalanced condition.

As wel, the gas check ensures that the base of the bullet is hit solidly by the pressure front, assuring expansion of the bullet base (obturation) which gives you better accuracy.

There are strange folks out there who have run cast bullets as fast as 3000 t/sec while using gas checks. I am not that adventurous by any means, being of the opinion that the .303 represents the latest in desirable technology! My 1896 Sparkbrook Lee-Enfield likes them, I do know that much.
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