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Joined:
May 2026
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VA, USA
Posted: 5/30/2026 11:33:48 PM EDT
[Last Edit: crob][Edited]
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I just finished putting together a new AR-15 build and am running in to a problem which I am unsure how to proceed with addressing. I got it all together and adjusted the gas block to a perfect 4 o'clock ejection with the suppressor on. But now when shooting either suppressed or un-suppressed, the rifle shoots fine in semi auto, but when going in to FRT mode if suppressed it will cycle and shoot 2-3 rounds fine, and then on the following round it will have a very light primer strike (as if it's getting bolt bounce, but it shouldn't be because the buffer spring, buffer, and gas system are all specced properly, see below parts), but if I remove the suppressor and shoot it un-supressed in FRT it will shoot 1-2 rounds and then will FTL the next round, as if it is under-gassed or has too strong of a spring/buffer which is on the opposite end of the spectrum for problems. I have ran the lower on my 14.5" and 16" 5.56 uppers and it has functioned flawlessly in FRT on both of those, so I do not think the issue is anything directly in the lower or FRT setup. Any help at all would be appreciated. Build parts: Griffin Armament MK II Upper/Lower/Handguard Geiselle SAE-X Trigger AS Designs ARC Fire FRT w/ stop block Tubb Precision Flatwire Buffer Spring Griffin AR-SOB Gen 2 Supressor Optimized Buffer (4.9oz) Griffin SN-ACH Gen 2 Charging Handle Rosco Signature K9 Series Melonite BCG Rosco / Sage Dynamics 10.5" Barrel Patrol Length Gas Tube (in between a carbine and mid length in size) Superlative Arms Adjustable Gas Block Rearden Single Port Muzzle Brake Rearden Plan B Mount Adapter Otter Creek Polonium 5.56 Suppressor Was just shooting 55 grain M193 5.56 ammo when testing. |
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Short version, unlike an auto sear in full auto rig, which the auto sear retains the hammer until the set gap of carrier to barrel extension face is retained, until the hammer is retained to strike the FP on bolt closure, FRT relies on your timing of pulling the trigger again each time, for hammer to drop to strike the FP as bolt is just staring to lock up. As for suppressor, short of low blow back 3d printed units, standard suppressors will speed up the cycle rate with high bore pressures, and in fact cause the bolt to unlock sooner as well. There is enough FRT write ups on the subject of tuning them on the net that No need for me to get deep into them, and since you know that the problem is with the faster unlock and cycle'g rate with rig suppressed, gives you the hint of what may need to be adjusted in the rig, to get a more favorable outcome with that type of trigger when rig is suppressed. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
Joined:
May 2026
Posts:
2
EE: 0% (0)
VA, USA
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Looked in to it more and made some adjustments with it, just want to be sure I've got this right though - without a flow through suppressor I likely will not be able to get the system working properly in FRT mode specifically on both suppressed and unsuppressed use due to the bolt bounce issue present in FRTs correct? I found the perfect setting to get the unit cycling flawlessly suppressed in FRT with no bolt bounce, but I have to back out 5 clicks on the adjustable gas block if I unsuppress it just to get enough gas to cycle the bolt back fully to lock position. Alternatively, if I leave it 5 clicks out so that it functions properly unsuppressed in FRT, I can still shoot in semi auto albeit it's gassed a bit high but won't be able to use it on FRT mode specifically. I don't know if I can make any other combination of buffer weights and springs to maybe get it working better than that and maybe get it to a point it can function in both suppressed FRT and unsuppressed FRT simultaneously without needing a gas block adjustment or not. While that would be optimal, I guess it isn't the end of the world because I mean to keep this rifle suppressed all the time anyway if it is not. |
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Originally Posted By jaqufrost: I would swap to a H3 and Sprinco blue. If that doesn't fix it, I would consider modifying the timing. Maybe, since what you are doing is slowing the unlock back down to normal buffer no suppressed, and heaver buffer or carrier weight when suppressed. Hence unless we are talking carbine stock, where the Carbine and H buffers are the correct length, you don't want to be using a Carbine length buffer or recoil spring in a full length receiver extension (not without a limiting spacer). Also to point out, although not that easy, there is adjusting the FRT in a way, so when you are allowed to pull the trigger again for the next round if rapids, it will have the carrier closer to the barrel extension so you not having the hammer coming down to strike the FP until the carrier is about to lock up. Hence your light primer strikes if correct weight buffer is in play/not a problem with bolt bounce, is that your pulling the trigger too fast after reset, and hammer is striking the FP with it still blocked by the carrier. To see this, B/C in hand and pull the bolt forward, push the FP all the way forward, and will note that until the bolt is starting to lock up in what would the barrel extension lugs the last of the way, FP is not allowed to protrude out the bolt face. Simply, trigger pulled after reset too soon, hammer strikes FP, but since bolt is not on it way locking up in the barrel extension, FP can not protrude out the bolt face, and all the energy of the hammer to FP is lost on hammer just helping to lock the bolt up faster by pushing it faster forward (not enough rapid primer strike to set it off, only dent the primer in the end. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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