Flash hider torque specs that cause accuracy issues

**Eurodriver** · 03-27-19, 21:50

Someone besides me has to have done it.

You go to install a suppressor mount and you think you’ve got the torque wrench set to 25 ft lbs and it ends up not being set at all so it never clicks. Next thing you know you’re at the range getting 30” groups at 50 yards.

The above happened to me with a 12.5” bcm. I removed the FH and the problem went away however that FH attached to any other rifle in the future always had accuracy issues that were so bad I worried about baffle strikes. I ended up throwing it away.

It got me wondering how much torque I put down and how much is needed to replicate that. I usually torque to 25, but have mistakenly torqued to 35 and that even seemed to cause accuracy issues though not to the same extent 90+ did.

Thoughts?

**Five_Point_Five_Six** · 03-27-19, 22:24

I bought a used Colt upper some years ago that had the birdcage threaded all the way up to the shoulder without a crush washer. I wasn't getting 30" groups but they were bad. When I went to remove it, I thought I was gonna need a breaker bar. Once I got it off, added a crush washer, and retorqued to spec, accuracy was fine.

If I had to put a number on it, I'd say it was torqued to at least 75 ft lbs or more.

**opngrnd** · 03-27-19, 22:28

This is why I use shims now.

Edit: By "shims", I mean accu-washers.

**MQ105** · 03-27-19, 22:36

1/2 x 28 threads? I know over torquing can affect accuracy, but not to the extreme that you describe. Something else was going on there - like a MD problem, as you indicated.
It's also possible that "over" torquing doesn't have a noticeable affect on accuracy at all. I did an experiment on a DD 14.5" with an A2 FH with torque values from 20-70 ft-lbs in 10ft-lb increments and had no difference in accuracy. I also had a 12.5" that showed approximately 100% increase; 2.5" 10 round groups @ 100yds with 25 ft-lbs, increased to 5" with torque value of 50 ft-lbs. So, I believe that recommended FH torque should be used, but high torque doesn't automatically mean problems. (shims used on all MDs)

**Clint** · 03-27-19, 22:52

It's not a problem with our *big* 5/8-24 threads...

**MQ105** · 03-27-19, 22:54

^^^

I'd like to see this, at least as an option, on more barrels and MDs.

**vicious_cb** · 03-28-19, 00:31

I shim then hand tighten with rocksett the MDs on all my barrels now. Never had one come off.

**Jsp10477** · 03-28-19, 05:26

Originally Posted by Clint

It's not a problem with our *big* 5/8-24 threads...

This.

**Tigereye** · 03-28-19, 05:51

When I built a 3 gun rifle, I put on a MD with crush washer and torqued to 25. The rifle would not shoot better than 1.5" groups with a match barrel. Very frustrating and disappointing. 2 years later I put an AFAB with shims on a new rifle and decided to try the shims on the 3 gun rifle. Groups shrank to .5".