Know what you're getting into with AAC QD rifle suppressors

[MCMXI]

AAC makes excellent suppressors, no doubt about it. I have a couple of the ELEMENT2, a TiRANT .45, a TiRANT 9S, an M4-2000, a 762-SDN-6, a MK13-SD and a TiTAN-QD. In terms of the materials used and overall quality I have nothing but good things to say. The problem is that they didn't fully engineer the QD system on the rifle suppressors that use 18T, 51T or 90T muzzle brake/flash hider interfaces. Conceptually their cam/ratchet QD design is great and it probably worked really well in the prototype phase when everything was hand fitted. However, once in production, and with tolerance stacking on the brakes/flash hiders and suppressor internals, coupled with the fact that even with the 90T brake there's 4° between "teeth" on the locking ring, there's just no way to maintain the necessary relationship with the suppressor and brake. What I've found is that I need to time each brake to the suppressor. This means polishing material off the locking "cone" such that the suppressor internal locking surface makes hard contact with the brake/flash hider cone right as the trailing faces of the two teeth on the locking cam make full contact with the leading faces of two teeth on the locking ring. This is a pain in the butt for sure.

AAC claims that even though the QD supressors can rotate back and forth through some nominal angle while "locked" on the rifle, there's no deleterious affect on accuracy. This is total rubbish since I've seen accuracy go to hell in a hand basket on all four rifles as a result of the suppressor shooting loose. I apologize for the rant but AAC could have, and should have, done more to resolve this issue. Now I'm buying Dead Air Armament suppressors since they seem to have built a better QD mousetrap. Once Dead Air expands their lineup to .338 caliber and pistol suppressors they'll put a big dent in AAC. Having said all that, the AAC rifle suppressors are well made, do a great job of reducing noise, and when not shooting loose are very accurate. I wouldn't be looking elsewhere if not for the QD system as designed and would most likely be a happy camper had I bought the direct thread models instead.

 

[horsemen61]

Good to know thank you for the info

 

[Ryanxia]

I'm waiting on my stamp to pick up my AAC 762-SDN-6.

Since I don't have it yet it's hard to visual what you're saying about polishing the teeth. Is the purpose to polish the teeth on the brake so they have a better angle against the locking teeth on the suppressor?

 

[MCMXI]

Ryanxia, I've ordered a number of AAC QD suppressors for others over the last year and they've been shipping with brakes/flash hiders. When I bought mine back in 2013 they didn't come with muzzle devices. I'm guessing that AAC tries to mix and match to find a brake/flash hider that times up with the mating surface inside the suppressor to reduce the number of complaints. Anyway, if you refer to the image below, the red arrow points to the surface that might need to be polished such that the suppressor and brake make hard contact right as the locking teeth mesh optimally. When you depress the locking lever/cam and screw the suppressor on, eventually the mating surface inside the suppressor will make hard contact with the bevelled surface on the brake (red arrow). If the teeth on the locking lever and the teeth on the brake aren't aligned optimally, or not at all, the suppressor is going to be able to rotate back and forth some amount. There's a cylinder on the brake that helps align the brake to the suppressor but the fit is sloppy and closer to an RC8/RC9 loose running fit than the other end of the scale like an RC3 or precision running fit. AAC states that carbon fouling fills in the "gaps" and locks the suppressor on. That's not a good engineering approach in my opinion. They also claim that the loose suppressor doesn't hurt accuracy but that's BS. I've seen first hand that it does affect accuracy and precision.

 

[Ryanxia]

Excellent. Thanks for the information.

 

[MCMXI]

Yesterday I "timed" the 51T flash hider on my POF P308 and now the fit of the suppressor is perfect. There's zero movement of the suppressor with the cam clicking into the proper position once the suppressor makes hard contact with the chamfer (A) on the 51T. I used a blue Sharpie and some good emery cloth supported by a small file to mark and polish the chamfer until the cam lever clicked into place with a reasonable incremental torque after the suppressor and chamfer make hard contact. Interestingly, you can monitor your progress as the protrusion of the cam lever increases (relative to the outside tube) as material is removed. Once the critical dimension is reached, the cam will suddenly click into place and you're done. I now have to time two more 51Ts for a couple of AR15s that host an M4-2000. I also have to time a couple of 90T brakes for a TiTAN-QD and MK13-SD. As I stated before, AAC makes great suppressors, and their QD system is superb in theory but hard to implement with typical production tolerances. Luckily it's not too difficult to fix. Also, the fewer the teeth (18T > 51T > 90T), the greater the angle between teeth which would necessitate the removal of more material to obtain proper timing.





This photo/schematic shows the ideal relationship between the teeth on the cam lever and the toothed ring on the 51T when everything is timed correctly. Hard contact with surface A prevents the suppressor from screwing on any more, and hard contact between the rear tooth surfaces on the cam lever and front tooth surfaces on the 51T prevent the suppressor from unscrewing. The only way that the suppressor can move is to depress the lever to disengage the teeth.




In the example below the timing is off. If the suppressor is able to make hard contact with chamfer A but the teeth of the cam are not engaged as shown above, the suppressor can unscrew and there will be excessive play and subsequent movement of the suppressor. According to AAC this won't affect accuracy but that's BS based on my experience with a number of their suppressors.




If the indexing is off, the cam lever will protrude above the surface of the tube when the suppressor is screwed on as tight as possible. When the timing is correct, the cam lever is flush with the tube when the suppressor is screwed on as tight as possible.

 

[horsemen61]

cool thanks for the new info

 

[Charger442]

one of the biggest reasons i dont own an M4-2000.

 

[MCMXI]

one of the biggest reasons i dont own an M4-2000.

I can't argue with that. I started this thread to help people make an informed decision based on my experience. I have zero regrets with my AAC suppressors that includes an M4-2000 but I'm not opposed to tinkering. I will say this though, if AAC had perfected their QD system it would be one of the best on the market, if not the best.

 

[horsemen61]

so MCMXI are you saying you like the 90T better than the 51T?

 

[basicblur]

I'm curious - if it's not mating "correctly", could one just drop back to the next tooth?

I've heard (maybe earlier in this thread?) that this is the reason AAC is now sending their QD cans with a free QD mount.

I also remember reading somewhere that someone was complaining about the same problem(?), and AAC told them it's a retention system, not a tension system.

I currently own an M4-2000 - will have to try it out - the few times I've been to the range with it, it seemed to lock up tight - thought I might have been able to force it one more tooth, but did not want to push it.

I have a 762-SDN-6 on the way - same mounting system, so I'm keeping an eye on this.

 

[MCMXI]

horsemen61, if you need to "time" the suppressor as described above, you won't need to remove as much material with the 90T brakes compared to the 51T muzzle devices. 90T = 4° between teeth, 51T = 7° between teeth. Whether you buy 51T or 90T will depend on the suppressor you choose. I had to buy 90T brakes for the TiTAN-QD and Mk13-SD suppressors and 51T flash hiders for the 762-SDN-6 and M4-2000 suppressors.

 

[MCMXI]

For the record, I stated that AAC is most likely mixing and matching muzzle devices to suppressors to reduce the number of complaints.

I'm curious - if it's not mating "correctly", could one just drop back to the next tooth?

You could, but with 7° or 4° between teeth there will be a lot of play between the suppressor and muzzle device. As I mentioned earlier, the fit between the cylinder on the brake/flash hider and the cylinder in the suppressor isn't tight so the suppressor can wobble around. Once you time the brake/flash hider, the fit is very tight with no movement, but the suppressor is easy to put on and take off.

I also remember reading somewhere that someone was complaining about the same problem(?), and AAC told them it's a retention system, not a tension system.

I think this is AAC spin. If no tension system was needed, they should have ensured a much better fit between the suppressor and the brake/flash hider.

 

[Ryanxia]

Thanks MCMXI. Good information. Once my stamp comes in for the 762-SDN-6 I will immediately start looking closely at this.