So it's been told by the "experts" on here that a SBR specs can be changed if it's not a "permanent" change on a form 1. So does the same apply to form 4 SBR? My real question is what about Suppressors that's on form 1? What about form 4 suppressors? Could we change calibers if we keep the original baffles? That's a million dollar idea for you shppressor companies! Go ahead and take my idea and make billions.

You cannot change calibers on a suppressor.  If you Form 1 a 556 suppressor and are caught shooting it on a 308, you may have a problem.  Assuming you had properly marked the suppressor when it was built, you cannot change baffles even if you pay the tax again since it is already registered.  Just pay the $200 and build a new one.  Two is better than one...

You can shoot any caliber you want thru any suppressor and not risk going to jail.  You may go to a hospital but not to jail.

ATF used to allow caliber changes by original manufacturers (C2) but never for F1 items.  Then some smart guys wanted it in writing as a CYA so now caliber changes are taxable events.  The tube can be shorten due to maintenance but it can never be lengthened.  Internal replacement in same caliber by C2 is not manufacturing.  Wipes are now no longer taxable parts and end user replaceable.

Most people get a 308 can and shoot everything thru it (eg, 223, 22lr).  If your 223 marked F1 can happened to have extra clearance due to over usage or bad construction and 308 goes thru uneventfully, you are not in trouble.

ATF silencer FAQ

https://www.atf.gov/firearms/faq/national-firearms-act-silencers.html

Ah okay, Thought it was the same for all form 1 items.