I googled a little bit and didn't find the answer.

I'm planning a form-1 can and was wondering how much overbore is allowed?

What I'm saying is, typically, for a .30 caliber suppressor it is common to use a 3/8" drill bit.

So, when you put caliber on the form-1, you list 30 caliber, even though the hole is physically .375"

All manufacturers use over bore to avoid problems with concentricity and instability.

But the ones I have all list the intended caliber on the markings.