I think my .22 suppressor at 7.5" could be shorter and still be effective and a bit handier.  Is there a legal way to modify and existing form 1 suppressor to shorten it?  I suspect they don't care until they inspect it, then crap hits the fan, so I want to stay well back from that line.

Shorten and rethread tube, to use existing end cap.
DO NOT MAKE ANY NEW PARTS

Make and send this letter.

Dear ATF,
I'm notifying you to update the length of a silencer, on an approved Form 1.

Control No. (from your approved form)
Date of Approval (from your approved form)
Length to be updated to

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]

I have a 6" rimfire. Found out they started making extensions. Got written permission and added 2 cones. Sounds really pretty much the same.

thanks! gives me easy legal options!