Last year I picked up an AAC 556SD.
AAC was running the Damn The Man promotion and a local shop was doing $100 off for Black Friday. Too good of a deal to pass up.
Initial host was a 16" carbine gassed AR with a semi-auto carrier and an H2 buffer.
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Even with the RTV sealant I would get a fair amount of gas to the face. Charging handle is a BCM gunfighter.
I wasn't satisfied with my only suppressor host being an iron sights only rifle so I parted it out and put together a new upper.
16" mid-length. M16 carrier.
Now I was waiting on a UBR to finish out my lower build the way I wanted it so I put the new upper on my 3-gun lower initially which has a JP captive spring setup to mimic the JP Low Mass buffer.
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The volume of gas was much much less but I could still feel it on my cheek.
Then the UBR arrived and I had everything setup like I wanted it. Upper does not have a forward assist installed. I considered getting the gas-bleeding replacement that goes in the forward assist port because I thought that gas venting out of there might come right back into my face. That is not the case so my plan now is to leave the forward assist assembly out entirely.
With the setup as it is now.
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Mid-length gas. (not sure on gas port size.)
Standard low profile gas block (I figured I could always add an adjustable later if it was really warranted.)
M16 carrier, H2 buffer, bcm charging handle with RTV sealant.
I am getting no discernable gas to the face/cheek whatsoever.
Another thing that is harder to quantify is that it seems like the ejection port pop is markedly reduced. I always felt like my old carbine upper was way overgassed and the addition of the suppressor exacerbated that situation. New upper seems much much quieter as far as I can perceive it. I presume that delaying unlocking with both the added weight of the carrier and more properly regulated gas would give the gas more time to expand and cool, and let more of it vent out the end of the suppressor rather than back down the barrel.
Mid-length upper runs great suppressed and unsuppressed. Zero shift is minimal but honestly I don't plan to shoot it with the can off. Recoil is very mild and that is comparing it to my tuned 3-gun setup that simply doesn't move.
So in my experience an optimized gas port location, adding some mass to the equation and a few small tweaks to the upper setup have made a tremendous improvement in the performance of my suppressed rifle.
Ancillary benefit. The new upper is much more accurate than the old one.
Overall I am very impressed with the performance of the suppressor.


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