Re: Suppressor/Gunsmith question
Simple answer - if the gunsmith wants the device to give you the best fit, just send it. If you don't want to do that, just understand you might not have the best fit possible. In fact, don't be quick to blame the gunsmith if your device doesn't mount to the host properly. Even following the manufacturer's "specifications" is no guaranty for proper fit. If you send the device, simply include a copy of your approved form and ship it the same way you did your host.
Long answer from the sleep deprived guy if you care to read more rambling details...
If the gunsmith is wanting the device, it is likely because he wants to cut as tight a thread as possible for that specific device. The tighter, more precise fit helps to prevent the device from loosening under use. You can always have your gunsmith simply cut the threads to a looser tolerance, just do so knowing their could be fit issues.
I can't tell you how many suppressors (or suppressor adapters) I've seen from even the largest suppressor manufacturers that not only were not to their published specifications on the tightness of the thread geometry but are off regarding tenon length (which is the length of the thread on your host). Just a couple weeks ago we had two .30-caliber suppressors from a manufacturer whom a lot of folks on this site really seem to like. The suppressors had serial numbers that were less than 20 from each other. Neither suppressor had threads that were in spec and both devices were very different (i.e. one was way on the loose end and the other way on the tight end). Just last week we threaded a host for a pistol suppressor. The customer didn't want to even provide us with the piston from his suppressor and wanted us to just thread it to fit one of the pistons we had on hand (we stock that particular suppressor). Yep, you guessed it - we threaded to one of the pistons we had but when the customer showed up to get his rifle his piston was WAY too tight and wouldn't fit. In that case the customer choose to just buy the piston we used for test fitting because he has experienced too many suppressors loosening under use and did want a precise fit.
Sending the device isn't necessarily a bad thing and is often requested for good reason.
As mentioned you can send your device to your licensed gunsmith.
http://www.atf.gov/firearms/faq/gunsmiths.html
The ATF suggests you use a Form 5 to transfer the item to the gunsmith and then again back to you. However, it is NOT required and rarely done that way these days. Many years ago everyone filed Form 5s. The only Form 5s people tend to use these days is to government agencies as tax exempt transfers. For example, a local police department would have their suppressors transferred to them on a Form 5. If you decide to go the Form 5 route, understand the wait times for Form 5s are similar to the wait times for approval of Form 3s.
Lastly, the ATF changes its mind in rulings all the time. It keeps life interesting to say the least.
Hope this helps some.
Mark