Blackout 51t mount shoulders out and still has threads exposed?

Hi all. I recently picked up my first bolt gun that was not a hand me down. A Remington 700 .308 with threaded barrel. I bought a 51t blackout flash hider mount so that I can use my can on it. When I threaded the 51t on (no rockset yet), I can still see some exposed threads of the 51t inside even though the mount has hit the shoulder on the barrel. Is that normal? It is not the deep socket mount, either. From looking down the barrel end, I think I can see 3-4 full threads on the 51t.
Should I be concerned?

No, it is not normal. The end of the threads/end of the barrel should be against the inside of the flash hider. Can you post a picture?

AAC made some special 51T mounts for the SCAR17 barrel, you might have picked up one of those.

Need a pic. If you mean there's still threads inside the mount, furthest away from the crown, then I don't see an issue. I have A2 flash hiders like that.... where they're threaded inside beyond where the barrel threading could reach.

What you describe is perfectly normal. As long as the end of your barrel was threaded correctly and is flush to the shoulder, you are good to go. AAC muzzle devices are threaded for about an inch+ so there is plenty of extra "female" threads.

Another way to look at it is, it ok to have threads inside the flash hider that are not being used. You do not want barrel past the mount because you will corrode the threads and never get it off. So not using some mount threads is expected. If thats what is going on. Again, pic will help.

PB