Figured I would ask the group since I don't know what to do at this point. I got my Arsenal Bulgarian Flash hider in today and it does not screw all the on my SLR104UR. It seems the inside diameter was not milled out enough where it expands pass the threads. It goes on about 80% of the way but not enough to lock in. Has anyone else had this issue? I'm thinking I can possibly take a file to the inside but a bit scared to ruin the threads.

I had something similar with my 104 on the cone flash hinder. I forced it which seemed to have cut threads into the little solid part before the barrel threads

UPDATE: I literally worked it on back and forth for over an hour and eventually got it to click into place. The tolerances were ridiculously tight on the solid part like you mention and the flash hider I had to smooth out the metal by screwing it on and unscrewing. I have a really nice blister on my right hand now but the joy of my new flash hider is making me not notice it.

Mine fit no problem, sorry to hear you had an issue.

Be warned, these get HOT fast. If you melt the dump bucket it's a royal pain to scrape off the outside of the hider and cone.

Had same issue with certain FH and brakes on my SLR106ur. I just lightly sanded inside of flashhider threads and cleaned and lubed them which helped a lot but its still very tight last 2-3 turns. Has to do with tolerance of threads I believe. Mine came with cone brake that threads on smooth but my aftermarket krink booster is very tight.