Barrel threads won't accept adapters

[TradLife406]

Last year I built a 9mm SBR. 5.5" barrel. Decided I wanted to try a longer barrel so there wouldn't be as much can tucked under the handguard.

Decided to risk buying ballistic advantage barrel.
It won't take my tri lug adapter. They start to thread on then after a couple revaluations it stops. Threads are both 1/2-28. I think the original adapter was a kaw valley. Thought maybe buying a more expensive one and got a Silencer Co. the SC goes on even less.

Going to call BA tomorrow and see what gives. Might stop at scheels and pickup a direct thread adapter for my 9 K. See if that will work.

Anyone seen this happen regardless of brand?

 

[RockAndSage]

If you have a machinist friend, having those barrel threads looked at might be a good idea. If you've tried two separate adapters/devices, and both have the result, that sounds like the barrel's threads are the problem. Bad cut, wrong cut, etc. It may sound obvious but, just in case, whatever you do, do not try to force, or use a lube, etc, until they're checked out.

 

[waspocrew]

Agreed, sounds like the barrel threads are the issue if two different devices end up with the same result.

 

[Kaleb]

I had some 1/2 threads cut on a few rifles and used my 1/2x28 HUB from a evo as a go gauge so to speak. They all threaded up smooth. As I added suppressors I had one or two that the new suppressor wouldn't thread all the way on. I took a 1/2x28 die and chased the threads. I noticed the die would get to about the same spot and get tight just like the new HUB. I tightened the die a little bit worked it over the threads and problem solved.

It's my understanding that you have tolerances with them. If your barrel is on the larger side and the device is on the smaller side it's going to be tight. A very simple fix though with running the die over the threads. Mechanist can be pretty ocd about threads and cut them as perfect as they can. They don't want slop in them. I would imagine our adapters and such are much more mass produced. Neither are wrong but like I said if the barrel is threaded to mate something that is on the larger side of 1/2 threads and the device is on the smaller side of 1/2 threads it will get tight on you. I'm not overly handy and the couple barrels I've had to do this on was very simple. Takes longer to mount a scope simple.

 

[Kaleb]

https://www.brownells.com/tools-cleaning/general-gunsmith-tools/taps-dies/ar-15m16-flash-suppressor-die/?sku=080598529

For what it's worth this is what I have. I like have dies and taps for the sizes I use in the event threads need to be cleaned up from damage get glue off of out of etc. rarely need them but handy when you do. Rather than having to make a trip to a gun smith a lot of things like this can be fixed in 5 min at home.