KAC QDSS-NT4 Shim Question

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Predator
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KAC QDSS-NT4 Shim Question

Post by Predator » Tue Oct 13, 2009 7:18 pm

Quick question about the install I just did.

I put a KAC QD flash hider on a Colt 11.5" commando barrel and because the instructions said to use as little a number of shims as possible, I ended up using the .015 and .008 shims for a total of .023.

I basically went with the lowest number of shims as well as the thinest. with the shims at .023 the middle slot aligned perfectly at 12 o'clock with 23 ft/lbs of torque. FYI when I put a combo of less than .023, and torqued the flash hider it went past 12 o'clock. I mention this because it's definitely using the shims at .023.

Anyway I took it back off, cleaned the threads up real nice and applied the loctite type stuff that came with the kit and put it back on and torqued it to 23 ft/lbs and all looks great.

After doing this and feeling like I was all done, I noticed the chart on the back that shows numbers of shims to reach certain thicknesses. There is no thickness down around the .023 like I just did so I am now wondering if I need to re-do the whole thing and make the shims thicker? Did I make it "too thin"?

Thanks in advance!

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Post by post tensioned » Tue Oct 13, 2009 8:20 pm

No,

As long as it's timed right, your fine.

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Post by Predator » Tue Oct 13, 2009 8:46 pm

Cool. That's what I thought but wanted to double check.

Thanks a lot! :D

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Post by Predator » Tue Oct 13, 2009 9:31 pm

Actually now I'm a bit curious about something else...

When you say "as long as it's timed right", what if it wasn't?

I mean what if I had the shims let's say at a thickness of .040, torqued the flash hider to 30 ft/lbs which put the middle slot at 3 o'clock instead of 12 o'clock. Now when I shoot the gun without the suppressor on the end I would imagine that it would have a tendancy to move the muzzle right because of how the slots are aligned, but would this also have some negative impact with the suppressor on? Does the suppressor need to be perfectly verticle in order to work properly? Hah, and If so then does that mean I can't do any bad ass mission impossible hanging from a rope upside down and shoot the gun becuase the suppressor wouldn't be directly up and down?

Sorry I'm just trying to understand the importance of having it timed at "exactly" 12 o'clock. Is it just for muzzle recoil or is there more to it?

Thanks and sorry for all the questions. I promise I'm done after this post! :oops: :D

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Post by 66427vette » Tue Oct 13, 2009 9:51 pm

mine is a little off center and has been fine for about 1000 rounds. no problems so far . should it be changed? it is about 1/8 of an inch past 12 o clock .

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Post by Predator » Tue Oct 13, 2009 10:32 pm

I just put another QD kit on another Colt upper I have, a 14.5" R0977 upper. This one I did at .062 and lined it up perfectly at 12 o'clock, but I only torqued it to 21 ft/lbs. If I torqued it more it would have gone past 12 o'clock obviously.

So now I have an upper with a very thin shim setup and one upper with a much thicker shim setup. Hopefully both will function flawlessly.

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Post by post tensioned » Wed Oct 14, 2009 9:47 pm

Not that I'm the foremost expert on this, and I'm sure they can chime in, but the timing on the flash hider is for the closed portion to be on the bottom to not kick up dust in prone shooting, like an A2, and I believe the suppressor index's to this to align the blast baffle to it. I can not imagine you would have any issues, other than the flash hider to ground relation and the quick release tab falling down if the retainer wasn't twisted on. I am curious myself, but I would bet there is no real issue with it.

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Post by 66427vette » Wed Oct 14, 2009 11:25 pm

Trey or Kevin should I remount mine if it is off 12 o'clock by about an 1/8 of an inch?

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Post by KevinB » Thu Oct 15, 2009 7:39 am

Not having it clocked properly in not going to cause a problem.

It will vent more gas to the side it is 'favoring' but nothing that will effect function or safe use of the suppressor.

One of the idea of the A2 and other 'clocked' flash hiders was that a right or left handed shooter could time it to push against the natural recoil path (up and left for a righty, and up and right for a lefty).
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Post by 66427vette » Thu Oct 15, 2009 6:31 pm

thankyou!

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