I recently finished a Form 1 9mm can. Works well.

Something I’ve noticed: before I ever shot it, the piston/booster assembly (from SD Tactical) threaded onto two different pistol barrels cleanly and smoothly.

Now, it’s hard to thread it on the Beretta and the 10/22, but easy to thread on the S&W.

At first it feels rough and I have to really put some pressure on it to get it to thread, but once I get it on there, it comes on and off almost as easy as the S&W. Feels like rough and smooth spots as I thread it on, if you know what I mean. Same on the 10/22 rifle with the same thread pattern.

What’s up with that?

Is it just that it’s dirty now? I’ve brushed and oiled the threads with no difference.

I’m pretty sure I haven’t damaged anything, as I said once the first rough threading is done, it’s relatively smooth.
Haven’t seen any metal shavings either lol.

Any input would be appreciated, I just want to make sure I’m not messing stuff up.

I had a similar problem.

I just bought a die, and chased the threads on the tight barrels.

Threads can be different class 1A/2A/3A for external and 1B/2B/3B for internal. Class 1 is the "loosest" fit, class 3 is the "tightest" fit, and most everything you encounter is class 2, while most muzzle devices and barrels are (should be!) class 3.

It sounds like some of your barrels are on the larger end of the tolerance, and the can is on the smaller end. While it is a problem, it's the better problem to have... it's a real pain when the threads on a muzzle device of any kind are way too large and/or the muzzle threads are too small.

My suggestion is the same: get a class 3A die of the appropriate pattern, use threading lubricant, and chase the threads on the problem guns.

If cleaning them (both male and female) doesn't help, do as recommended above and chase with taps & dies

I urge people to run 2A threads on muzzles, encountered more than a few brakes and comps that were an interference fit with 3A muzzle threads.  I also knock the crests down a couple thou.