I don't have headspace gages and have used fired f.l. sized cases to set headspace. Once the barrel is set so the bolt just closes on he fired f.l. sized case, I put a piece of scotch tape on the base of the case and try it in the gun-there should be resistance to bolt closing.
I'm a little goosey about using the fired f.l. sized case, and use several to make sure on the headspace.
Yesterday I filled a fired case with lead, melting to make sure the case was filled. he case was then a very tight or not fit. F.L. sized the lead filled case, it took a little force, and then tried the case. It fits in the gun with slight bolt resistance; and with a strip of scotch tape on the base it's a no-go or at least very heavy bolt resistance.
I have swaged lead into a case, many times, to slug the chamber. Pounding the lead with a rod and hammer. This would make a lead filled case an almost perfect fit in the chamber, and might be better than my new "almost a go gauge", but for now I'm happier than using an empty case as a gage. aybe overkill, but...
joe b.