Gunsmithing Torqueing down Muzzle Brake?

[Luva_n_FrenZ]

How are you guys torqueing down Muzzle devices on your bolt guns? Using a barrel clamp? Vise?

I have an AAC 51T Muzzle Brake I'll be installing on my Bergara HMR. I have barrel blocks, reactions rods, etc for AR builds but this is my first precision-type build so I want to do it right!

Thanks!

 

[NWnewguy]

I use a barrel vise and a 3/4" crows foot on a dial indicating torque wrench. Sometimes the barrels want to spin in the vise which sucks, but you can add a little rosin to the leather and it usually stops it, depending on how high you're torquing to will effect that a lot. You could spring for the SAC barrel vise and it would probably solve that problem all together. If you don't have a barrel vise you could also make clamping blocks out of hardwood for any half decent table top vise and that will also work just fine.

 

[Luva_n_FrenZ]

I use a barrel vise and a 3/4" crows foot on a dial indicating torque wrench. Sometimes the barrels want to spin in the vise which sucks, but you can add a little rosin to the leather and it usually stops it, depending on how high you're torquing to will effect that a lot. You could spring for the SAC barrel vise and it would probably solve that problem all together. If you don't have a barrel vise you could also make clamping blocks out of hardwood for any half decent table top vise and that will also work just fine.

Thanks! I have two blocks of 2x4 for a DIY barrel vise. If that doesn't net the result I'm hoping for I may cough up the dough for a legit barrel vise unit.

 

[TresMon]

Always go by torque spec. if you don't have specs and can't get them, just snug it. and call it good. its not hard to stretch the end of the barrel with the mechanical advantage of threads. Obviously this is more of a concern with smaller barrels, but still. I've seen this accuracy issue with people clocking a bird cage to the position they desire, no crush or peel washer on AR's

 

[MtnCreek]

Make sure you use hardwood like NWnewguy said. Pine or fur will not grip.

 

[Luva_n_FrenZ]

The AAC 7.62 MB calls for 45-55ft/lbs of torque, a bit excessive IMO. I'm afraid of warping the threads if I get anywhere toward that much torque.

Normally for my suppressor mounts, I add a drop or two of Rocksett and shim the device until I have 10-15 degrees of rotation left to align it.

 

[BurnOut]

The AAC 7.62 MB calls for 45-55ft/lbs of torque, a bit excessive IMO. I'm afraid of warping the threads if I get anywhere toward that much torque.

Normally for my suppressor mounts, I add a drop or two of Rocksett and shim the device until I have 10-15 degrees of rotation left to align it.

I'll do my best to shim them until my desired 12 o'clock position on the brake is at 10:30-11:00 relative to the action when the brake is hand tight against the shims/barrel shoulder, back it off, add a few drops of high temp red LocTite, and torque the brake on.

I use two small bubble levels (one on the scope rail, the other on the top flat of the brake) to determine my final installed position of the brake.

 

[Wannashootit]

Strap wrench works fine for me...
I've installed a ton of smaller brakes with only .500 of thread engagement that have a very fine (32 tpi) pitch so they are less prone to loosening from vibration. With the finer thread pitches I don't apply as much torque.

 

[Luva_n_FrenZ]

Strap wrench works fine for me...
I've installed a ton of smaller brakes with only .500 of thread engagement that have a very fine (32 tpi) pitch so they are less prone to loosening from vibration. With the finer thread pitches I don't apply as much torque.

Ahh... Good info about finer thread pitches. Makes sense!

 

[PatMiles]

Clock it and use red loctite 271 or Rocksett I've seen folks use small cheater bars to get the brake timed right and then wonder why the gun doesn't shoot worth chit anymore.

 

[David4570]

I am about to mount an AAC 51t flash hider on a Knight’s SR25 APC 308. AAC makes a special mount for the SR which has a 3/4x24 thread pattern. AAC calls for 90-100 ft-lbs of torque.
That sounds really tight based on the above comments and others. Anyone have this setup and care to share their experience?

 

[Luva_n_FrenZ]

90-100ft/lbs? That's more than the specs required for my Toyota truck lug nuts!

My AAC 7.62 51T MB called for 45-55ft/lbs (per packaging). It was a P.I.T.A to get it timed perfectly which took 40ft/lbs and I left it at that.

 

[David4570]

That spec is right on the back of the package. It’s kind of scary. It 2-3 time the othe mount torque values listed for different thread patterns.

 

[Luva_n_FrenZ]

Damn. Let us know how it goes with that. I'd be worried about warping the threads trying to achieve 90ft/lbs. I'm sure AAC has their reasons though.

 

[David4570]

I’ll be calling Knight’s to see if they can provide any advice. I can’t be the only one trying to use a 762SDN6 on one of their rifles.

 

[MOUNTIC]

I would never torque any muzzle device on my SR25s at that. Ever. Wouldn't even come close. I was told by KAC that you "can time the MDs as low as 15ft lbs and generally advise not going above 35. Clean threads on both with brake cleaner. Use rocksett. Snug it up. It will never come off on it's own. If you try torquing it to 100, you will be sending that barrel back to KAC for a replacement. And that's not cheap.

 

[XLR308]

Tightening a muzzle device doesn't need to be complicated or destructive.
And the torque values listed on that AAC package would fall into the destructive category in my opinion considering most barrels are 416ss and would result in a trip to the gunsmith to have them removed or the threaded portion cut off and rethreaded because the threads were dry with a locking compound applied and then over torqued.
Another issue with over torque at the muzzle threads is inadvertainly creating a choke point at the muzzle due to thread elongation and would be detrimental to accuracy.
The Surefire brake I installed on my 68spc called for I believe no more than 19ft lbs when properly shimmed for timing and Rocksett applied, it's been on there for about 8 years now and has been trouble free and I bet I could also get it back off without trashing the muzzle threads or break with little effort.
If you want a damn good barrel vice for minimal money look at the Viper vice they are perfect for switch barrel set ups and routine tasks like installing muzzle devices and tightening barrel nuts in a way that puts no stress on AR receivers.
I tighten the barrels on my Kelbly actions to 98ft lbs without any rosin on the vice or barrel while only snugging the four clamp bolts down not gorrila strong arming them and have no slippage.

 

[MOUNTIC]

Here are KACs muzzle device timing instructions that came with my 7.62 MAMS for the SR25. 3/4x24.

Torque with proper shims to get close with 20-30 ft lbs. Then clean and degrease threads. Apply rocksett and tighten to 15-20 ft lbs of force to 12oclock position +/- 3 degrees.

 

[David4570]

You guys are right and I’m glad I didn’t just jump in without consulting a couple sources. JackL over on the Knight’s ARFCOM page confirms “NO MORE THAN 20 FT-LBS”.

Unfortunately, after getting a “Knightstick”, SNAP-ON 22mm crows-foot wrench, Knight’s 7.62 shim kit and the AAC FH I’ve run into a snag.

I got home early today and started the project. I’ve put a few AAC muzzle devices on 5.56 and 300 BO barrels with good results. Yes, I get some ringing which I don’t hear with Knight’s 3-prong FH. Knight’s design is clearly superior given their prongs each have a different mass. Great design.

BUT, the new FH won’t tighten before it hits the hand guard. Now I don’t think I’ll be saving anything.

I was happy to see that there is a very nicely cut recessed crown on the end of the APC barrel.

 

[David4570]

Thanks for sharing your experience guys!

 

[XLR308]

Did I hear you correctly , the muzzle device hits the handguard before tight ?
Or do you mean your wrench will contact the handguard while trying to tighten ?
If it's the wrench just pull the handguard install the FH and then reinstall.

 

[MOUNTIC]

Did I hear you correctly , the muzzle device hits the handguard before tight ?
Or do you mean your wrench will contact the handguard while trying to tighten ?
If it's the wrench just pull the handguard install the FH and then reinstall.

You can't pull that handguard on the SR25 without the KAC special gas block castle nut removal tool and the KAC wrench to take off the rail. As it's the barrel nut and rail built together. Gas block has to come off first before you spin the rail off. And you either have to use a special puller to get the gas block off after the nut comes off, and they are usually very stuck. Even on new guns.

 

[MOUNTIC]

You guys are right and I’m glad I didn’t just jump in without consulting a couple sources. JackL over on the Knight’s ARFCOM page confirms “NO MORE THAN 20 FT-LBS”.

Unfortunately, after getting a “Knightstick”, SNAP-ON 22mm crows-foot wrench, Knight’s 7.62 shim kit and the AAC FH I’ve run into a snag.

I got home early today and started the project. I’ve put a few AAC muzzle devices on 5.56 and 300 BO barrels with good results. Yes, I get some ringing which I don’t hear with Knight’s 3-prong FH. Knight’s design is clearly superior given their prongs each have a different mass. Great design.

BUT, the new FH won’t tighten before it hits the hand guard. Now I don’t think I’ll be saving anything.

I was happy to see that there is a very nicely cut recessed crown on the end of the APC barrel.

Sr25 muzzle devices index off of the crown of the barrel. So looking in your muzzle device you should have a 90° stop. The shims sit inside the MD. If the threads are continuous into the MD then it's not going to work.

 

[XLR308]

You can't pull that handguard on the SR25 without the KAC special gas block castle nut removal tool and the KAC wrench to take off the rail. As it's the barrel nut and rail built together. Gas block has to come off first before you spin the rail off. And you either have to use a special puller to get the gas block off after the nut comes off, and they are usually very stuck. Even on new guns.

Sounds like they designed as many problems as possible into the system, nice rifles im sure but damn Cleatis.

 

[David4570]

All true comments above. I’m dealing with a great albeit proprietary system. I was hoping to save about a grand using my AAC suppressor. Removing the hand guard is not easy and wouldn’t work for me with the AAC anyway.

Plan “B” is to save up for the Knight’s PRS can. That will take a while but it will be “right” when done.

 

[motorcycleboy]

I watched a really good video about installing muzzle brakes a while back. You shouldn’t torque them down at all. No washer at all. Use red loctight and oriantate short of bottoming out the threads and let dry. Torque on the threading changes with heat and causes vertical stringing. More stringing with more torque on muzzle devise.

 

[Wannashootit]

Interesting point worthy of discussion IMO.

I recently saw another demo proving that threading to too thin a barrel wall thickness opens up the bore in the area of the tenon - a point that was easily proven with gage pins before/after threading. I suspect that the dimensional changes to which you're referring above would also be affected by barrel wall thickness and pitch diameter.

 

[BurnOut]

I watched a really good video about installing muzzle brakes a while back. You shouldn’t torque them down at all. No washer at all. Use red loctight and oriantate short of bottoming out the threads and let dry. Torque on the threading changes with heat and causes vertical stringing. More stringing with more torque on muzzle devise.

The problem with this is that any slop between the muzzle threads and the threads on the muzzle device then becomes a part of the installed orientation of the muzzle device. There's a reason that the folks that manufacture some of the most precision-oriented suppressors on the market (Thunder Beast) recommend seating a muzzle brake/suppressor mount against a squarely machined barrel shoulder.

No one's saying that you have to go all King Kong on the muzzle device torque, but there does need to be some load on the threads (between the muzzle and the muzzle device) in order to remove any "slop" from the interface.

 

[Strykervet]

I’ll be calling Knight’s to see if they can provide any advice. I can’t be the only one trying to use a 762SDN6 on one of their rifles.

SDN6? 90ft.lbs.! I have two of those cans. First off, the mounts jiggle to wobble --unless you wanna fuck with grinding that taper face down, you're gonna wanna order about ten of those mounts and pick the one that locks up tight, send the rest back. Trust me here, with four AAC cans using those mounts I've tried it all. The brakes aren't bad at all, the Brakeout isn't TOO bad, it isn't too great either. Doesn't ping! though.

So when I install 'em, I get 'em lined up with AAC shims until it stops at about 10 o'clock, then tighten down from there (depending on thread size). I'm not using a torque wrench. I'm also not having any problems either. And what KAC says sounds FAR more in line than does 90lbs! With threadlocker, it doesn't really take a whole lot to hold those mounts on. I've never had one come off or work loose before.

 

[Strykervet]

Also, I took one look at the SR25 and it's mount and said "fuck AAC" and got the KAC suppressor. It's the titties, it's a nice can. It's also lighter than an SDN6 and KAC flash hiders and brakes are way better.

All true comments above. I’m dealing with a great albeit proprietary system. I was hoping to save about a grand using my AAC suppressor. Removing the hand guard is not easy and wouldn’t work for me with the AAC anyway.

Plan “B” is to save up for the Knight’s PRS can. That will take a while but it will be “right” when done.

I'd stop and just go with plan B now. I have the QDC, the PRS can wasn't out then. Whatever you do, you want the full length KAC can, their short ones are just moderators.