An inherited 20's Commercial - too little headspace?

[MileMarker81]

Hello.

I recently inheritied a 20's Commercial from my mother-in-law's estate. It was her father's gun so it has quite the sentimental value.

All the numbers are matching but there is no clip.

My boys (a 17yo and a 20yo Marine) want to shoot it at least once. The Marine will be taking his pre-deployment leave in about 6 six weeks, so I have until then to make sure that it's safe to fire.

I've stripped, cleaned & inspected all parts and there is no obvious wear or cracks. The action is smooth. So far, so good.

I rented a Go/No-go gauge set from an online gunsmith supply shop and the breech fails to fully close on the GO gauge.

To double-check I made sure that everything was clean and checked the gauge demensions against the published SAAMI specs and it all checks out again. Hmmm.

Do firearms lose headspace with age? It seems odd to me. Could this be a matter of old tolerances vs. new tolerances? All of the appropriate Nitro proofs are present so it had to be checked at least once in it's life.

What do you guys think?

Thanks in advance,

Rob