Quote Originally Posted by PaddyD View Post
You make a great point there. I once read an article about a guy taking a full length sized case and filling it with devcon epoxy and using it for a go gauge. He filled it with epoxy so it wouldn't be able to squeeze down while he screwed his barrel down on it. I wouldn't trust a case like the modified Hornady because you just never know how exact it is. They say it is the same, but how would you check?
The go-gauges I have measure exactly the same as their corresponding Hornady modified cases. All you need is a headspace comparator or a headspace micrometer to measure them.
The most important measurement is from base to shoulder datum. In this they measure EXACTLY the same. Rest of the dimensions are the same as well.

I don't think a piece of brass will conform when being pushed by a barrel that's being screwed on. I've checked HS on rifles with the modified cases, and when attaching masking tape to their head (to turn them into a no-go gauge) they give a very positive feel of hitting a wall when attempting to close the bolt.