I submitted my app a few weeks ago for a 5.56 can. I meant to withdraw it and resubmit as a .30cal. I got busy and forgot to send the letter.

Well, I got the stamp in my email today sooner than I expected.

I haven't made any parts yet so I wouldn't be modifying an existing NFA item. What's the process for requesting a change to the caliber on the approved stamp?

I guess I could still bore the baffles for .30 cal clearance but my OCD would bother me that it's marked 5.56.

I have other .30 and 5.56 cans so I'm not in a rush if the best way is to withdraw and resubmit.

Worst case I could keep it and submit a new one but I don't really need another F1 5.56.

Most 5.56 cans are usually bored around .300" anyway, technically it would be fine as is.

I usually run about .020-.030" clearance per side. Less on shorter lengths. Last 5.56 I did was about .275" for the baffles on a 6".

For an 8" .308 I would prob go .350-.370". I think I did .370 on my last one.

Technically, it's fine. I'm just OCD about having my ".30 cal" can marked as 5.56 if I'm putting this much time into the parts and coating.

You can make the hole as big as you want as long as the stated caliber on the engraving can fit through it.

ETA: You can jump on the Ask the Expert on the eform site and ask them.  There is an email addy that you'll get that you can send an email requesting the change.

It's easy

This has been my standard, email, format: (notice the simplicity)

Dear ATF,
I'd like to amend the length/caliber, of an unbuilt silencer, on an approved Form 1.

Control No. (from your approved form)
Date of Approval (from your approved form)
Length to be amended to or Caliber changed or both

Thank you,
Mr. Jon Hancock
-sign here in ink- <---VERY IMPORTANT

You can scan the signed letter and email to
[email protected]
[email protected]
[email protected]