I had my Scorpion barrel threaded for 1/2-28 2 months ago. When I received my silencer (Gemtech) attachment (LID), the threads are a little to tight...IOW, I'm afraid to go past 1 turn. The gunsmith is an airline pilot by day and due to his and my schedules I have not been able to get in to see him. The fact that its 50+miles to his shop hasnt helped.

What is the risk if I bought a die and chased the threads myself?

first get a thread gauge and make sure they are actually 28 tpi... if he used a lathe the setting could be off, or if he used a die, he may have grabbed the wrong one...

if you are sure of the adaptor threading, and sure the barrel threads are the correct pitch you should be able to start a die on there by hand, then drop the handle on the die and chase them down using lots of oil...

But if the pitch is off, you will destroy the threads and the end of the barrel will need to be cut off and a new set of threads cut. But if the threads are the wrong pitch, that will need to be done anyway unless you can get an adaptor from gemtech for whatever they actually are.

I think it was his goal to get a class 2 fit but unfortunately my LID wasnt in so he used his AAC silencer to get a snug fit. I believe the pitch is good but the peaks maybe to high.

IMHO, there is no reason for a "professional" to be matching threads on anything unless specifically requested to do so. A set of thread-wires is $20, a mid-grade 0-1 mic is $50-75. For less than $100 he could have made your thread to the true specs desired (class 2 or class 3). Every single barrel threading job I do the pitch diameter is checked with mics and thread-wires. I have a guy that just emailed me last week, over a year after I threaded his barrel, expressing how perfect and smooth the thread-job is and how he is still super pleased at the job I did. He said the fit is perfect, snug, but not too snug.

I thread every job with class 3 threads unless requested otherwise.

That being said, it's going to be nearly impossible for him to match back onto those threads and take just a bit more off with the lathe. If he can do that he's a better man than I am.

My preferred solution to this problem would be to stop before you do anything. Verify the pitch diameter of your barrel using the above method I mentioned. If the pitch diameter is right then the problem is 1 of 3 things. #1, it's the major diameter of the thread, #2 Its the minor diameter (in the root) of the thread, or #3 Your suppressor/mount is out of spec. If it's the barrel that is out of spec (most likely is from what you've told us) then you need to get a split die, open it up until it spins on freely, then close it down a little at a time so that it takes off only a small bit per pass, then check the pitch diameter. You will likely not be able to get a full thread form all the way back to the shoulder using a die. To finish off those last few threads you may have to resort to a 60 degree triangle file to actually remove some material in the root until your mount will thread on all the way.

When ever you are threading with a specific silencer in mind it should be done in accordance with that company's thread spec. Every barrel we thread gets class three or thread specs matching the make and model of there can based on published specs. We ask every customer what they prefer. That said if you went to the trouble of bringing your CZ in line with 922r compliance; I would have someone who knows their way around a lathe reacquire the threads and cut them according to GEMTECH thread specs.

GEMTECH Barrel Thread Specs Complete

And never forget no matter how many times you chase the threads they do NOT get larger.

I went back to the OG (original gunsmith) and he fixed them. Now just waiting on my silencer to get out of jail (day 127).

I would not use a die.  I'd put that puppy on the lathe and remove metal that way.

Ask you 'smith how he did it.

You can do very good work using a standard split die.

My master machinist routinely roughed out threads on the lathe and then finished to tolerance with a split die.

Split dies are something everyone should have in their smithin tool box.


http://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/taps-dies/dies/ar-15-m16-flash-suppressor-die-prod41592.aspx?psize=96