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FRT optimized 9mm AR? (Page 1 of 2)
Posted: 2/12/2026 8:15:42 PM EDT
[Last Edit: heavyduty][Edited]
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I have a RB in my MPX Copperhead-K that is running well, but I’m concerned about parts breakage and the difficulty in getting part replacements. So, I’m considering putting together a FRT optimized SBR 9mm AR of some flavor and using either the RB or my Partisan in that. Has anyone gotten a Foxtrot Mike 9mm to run reliably with a FRT? I know bolt carrier design is important, but I’ve never seen a FM in the flesh and know very little about them. Another option is rebarreling my ancient 16” AR9 that has a Colt pattern NoDak Spud lower. What do I need to be looking at for 9mm BCG features? |
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Originally Posted By heavyduty: I have a RB in my MPX Copperhead-K that is running well, but I’m concerned about parts breakage and the difficulty in getting part replacements. So, I’m considering putting together a FRT optimized SBR 9mm AR of some flavor and using either the RB or my Partisan in that. Has anyone gotten a Foxtrot Mike 9mm to run reliably with a FRT? I know bolt carrier design is important, but I’ve never seen a FM in the flesh and know very little about them. Another option is rebarreling my ancient 16” AR9 that has a Colt pattern NoDak Spud lower. What do I need to be looking at for 9mm BCG features? Regarding BCG features, you basically want three things: 1) a M16 style tail (sometimes listed as "full auto," "FA," or "M16" depending on brand); 2) either no weight occupying the interior of the rear portion of the BCG or one that is removable (often held in by a roll pin driven horizontally through two holes and through the weight toward the rear of the BCG); and 3) an intact bottom lug on the bolt face. As an aside, all of @Blowback9 's advice in this article is generally solid. I don't have a FM BCG, but based on the product photos, it looks like it will work If you're building the platform out from scratch, I've had great luck with the IDL Gen 3 9mm BGC. (See also @Blowback9 's review.) The IDL also needs the weight removed or cut. If you have a 10 oz buffer (like this one), you might even get away with just removing the BCG weight altogether, as long as you have 22-24 oz of total reciprocating weight between the buffer and BCG. Assuming everything works, consider cutting the removed weight and reinstalling to reduce your RoF. You could also consider getting a CMMG RDB Banshee upper in 9mm (in 8" or 5"), and using any standard AR/M16 lower with CMMG mags. No bolt mods necessary. An H3 buffer is totally sufficient for use with an FRT in that setup, including your RB. You wouldn't be the first to head down that path. I'm not sure the Banshee would work with your NoDak Spud without actually trying it, though. - - - - I'm curious about your MPX: Are you planning on running another FRT in that? If so, have you decided which one? I heard about the wear the MCX puts on triggers, but there are several folks around where I live that have hundreds (not thousands) of rounds with their RBs in their MCXs without issue. Are you seeing wear develop in yours? If so, where? |
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| Contrary to the above, no cutting is needed on the weight in a FM 9MM bolt, it sits back far enough to not interfere. BCG Weight rounded up to 14oz, plus a 10 or 11 oz blowback buffer seems right in the sweet tuning spot. |
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Good info, everyone - thanks! Originally Posted By lugnutwrench2: I'm curious about your MPX: Are you planning on running another FRT in that? If so, have you decided which one? I heard about the wear the MCX puts on triggers, but there are several folks around where I live that have hundreds (not thousands) of rounds with their RBs in their MCXs without issue. Are you seeing wear develop in yours? If so, where? If I pull the FRT I’ll just go back to the stock Timney. But, on reflection I’m wondering if the change I made to a 0.0469 gas plug to tune it for suppressed calmed things down enough that the wear and breakage issues are less likely. It’s a stupid amount of fun, little bitty gun go brrrrrt. |
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I bought a FM9 specifically to run a Super Safety in. I modified the bolt, ground away the little shelf in the upper, and tried 3 or 4 different buffers and springs. Never got it to work in Super Safety mode. Bought a Lee lower for a MP5K clone and it purrs like kitten. |
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Originally Posted By heavyduty: Good info, everyone - thanks! If I pull the FRT I’ll just go back to the stock Timney. But, on reflection I’m wondering if the change I made to a 0.0469 gas plug to tune it for suppressed calmed things down enough that the wear and breakage issues are less likely. It’s a stupid amount of fun, little bitty gun go brrrrrt. Originally Posted By heavyduty: Good info, everyone - thanks! Originally Posted By lugnutwrench2: I'm curious about your MPX: Are you planning on running another FRT in that? If so, have you decided which one? I heard about the wear the MCX puts on triggers, but there are several folks around where I live that have hundreds (not thousands) of rounds with their RBs in their MCXs without issue. Are you seeing wear develop in yours? If so, where? If I pull the FRT I’ll just go back to the stock Timney. But, on reflection I’m wondering if the change I made to a 0.0469 gas plug to tune it for suppressed calmed things down enough that the wear and breakage issues are less likely. It’s a stupid amount of fun, little bitty gun go brrrrrt. I've got 1k+ rounds through my MPX-K with the RB that has their name on the side and a PMM trip bar. I shoot primarily 124gr bullets with 4.2gr N320 which dependent on bullet and seating depth runs 1050fps to 1100 fps MV. I always run it with an Omega 36M in the short configuration. I notice a big difference in trigger slap between these loads and factory loads that are hotter. It is very pleasant to shoot, and not gassy at all with my loads. Other than the trigger/trip, mine is factory. The first trigger I put in it was one of the RB triggers they obtained and sold from Delta Team Tactical. It didn't last very long, before it started double firing in position 2. So far, the new one hasn't shown any issues, and as I said it has 1k+ rounds on it. |
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Originally Posted By ELittlefield: Here's the KAK tungsten bolt weight: no cutting required, and it adds additional weight. https://i.imgur.com/UKBcyIX.jpeg" target="_blank">https://i.imgur.com/UKBcyIX.jpeg pic of the ass end of the bolt? you sure it's completely flush back there? |
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Originally Posted By MaxTheRabbit: pic of the ass end of the bolt? you sure it's completely flush back there? Originally Posted By MaxTheRabbit: Originally Posted By ELittlefield: Here's the KAK tungsten bolt weight: no cutting required, and it adds additional weight. https://i.imgur.com/UKBcyIX.jpeg" target="_blank">https://i.imgur.com/UKBcyIX.jpeg pic of the ass end of the bolt? you sure it's completely flush back there? It sticks out a tiny bit. Still closes up though. I haven't shot this yet.  " /> |
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Originally Posted By ELittlefield: It sticks out a tiny bit. Still closes up though. I haven't shot this yet. [url]https://i.imgur.com/zg1PO1D.jpeg">https://i.imgur.com/zg1PO1D.jpeg">[url]https://i.imgur.com/zg1PO1D.jpeg |
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Originally Posted By shultz: I'd flip that weight around. That's a lot of constant beating/stress for a small roll pin to take... Originally Posted By shultz: Originally Posted By ELittlefield: It sticks out a tiny bit. Still closes up though. I haven't shot this yet. [url]https://i.imgur.com/zg1PO1D.jpeg">https://i.imgur.com/zg1PO1D.jpeg">[url]https://i.imgur.com/zg1PO1D.jpeg Ok. Thanks for the tip. Shouldn't get in the way, because it's a Rare Breed (fuck Rare Breed). |
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The FM bolt I have beats on the hammer pretty hard. It seems like the bottom edge hangs considerably lower than other bolts. Mine ran fine with the internal weight removed on another bolt, a light buffer and a 308 spring. Had a silly high fire rate, and when I tried to turn that down for my kids to shoot it, I got all kinds of out of battery detonations. On mine the trigger will pull with the bolt way back. |
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Originally Posted By Karankawa: The FM bolt I have beats on the hammer pretty hard. It seems like the bottom edge hangs considerably lower than other bolts. Mine ran fine with the internal weight removed on another bolt, a light buffer and a 308 spring. Had a silly high fire rate, and when I tried to turn that down for my kids to shoot it, I got all kinds of out of battery detonations. On mine the trigger will pull with the bolt way back. You can mask this timing issue by using a stiffer recoil spring like 308. The bolt is moving home so fast it gets there before you can drop the hammer too early. This assumes the bolt doesn't bounce because of the really stiff spring... |
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Originally Posted By shultz: What FRT? Lever type like the Atrius, cornfire MARC and even the super safety all be it to slightly less extent in my experience will all allow you to drop the hammer early. Lack of an out of battery safety and trigger tail/cam geometry allow excessive trigger finger pressure to override the cam/lever forward until the hammer drops. You can mask this timing issue by using a stiffer recoil spring like 308. The bolt is moving home so fast it gets there before you can drop the too hammer early. This assumes the bolt doesn't bounce because of the really stiff spring... It ran great with the 308, lighter parts and a Hoffman SS. The problem started when I tried to do the gentle recoil system and three position Atrius. I was also trying to make it easier to load for my girls. The 308 spring is a booger with no boot catch. Old PSA9. I tried using a Taccom bolt with the short stroke geometry. The bolt catch was wonderful but it seemed to trip the lever prematurely. Lots of hammer follow. I think your comment about timing is spot on. |
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Originally Posted By Karankawa: It ran great with the 308, lighter parts and a Hoffman SS. The problem started when I tried to do the gentle recoil system and three position Atrius. I was also trying to make it easier to load for my girls. The 308 spring is a booger with no boot catch. Old PSA9. I tried using a Taccom bolt with the short stroke geometry. The bolt catch was wonderful but it seemed to trip the lever prematurely. Lots of hammer follow. I think your comment about timing is spot on. For your girls,get one of the FRT'S that has an out of battery safety. The Arizona regulator, Partisan disruptor simply will not allow the user to pull the trigger unless the carrier has unlocked the out of battery safety. Timing on these FRT'S is solid. You can still get bolt bounce but that's easy enough to remedy. |
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Originally Posted By shultz: Yeah,slowing down the bolt made the timing issue worse making dead triggers and OOB'S more frequent. There's really nothing you can do with the lever type FRT'S to correct this sadly... For your girls,get one of the FRT'S that has an out of battery safety. The Arizona regulator, Partisan disruptor simply will not allow the user to pull the trigger unless the carrier has unlocked the out of battery safety. Timing on these FRT'S is solid. You can still get bolt bounce but that's easy enough to remedy. Will get those ASAP. Really having a tough time not buying gun stuff. My back gave out again and I’m recuperating from surgery on it. Not able to work for another month at least. There’s so much fun stuff on the market now just taunting me. I also think it’s important to support them and quality built FRTs may not be around forever. The DOJ helping rare greed get an injunction has me stressing about it. |
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Be careful about using 308 springs with blow-back 9s and FRTs. There's some argument/evidence that OOB detonations become more likely (i.e., the heavier spring increases the risk of bolt bounce): https://blowback9.wordpress.com/2021/08/09/what-9mm-buffer-do-i-need/ Consider lighter springs and heavier weights first for slowing RoFs. Take this with a grain of salt, however. I've done a lot of reading, but much less actual shooting across PCC platforms. |
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Originally Posted By ELittlefield: Ok. Thanks for the tip. Shouldn't get in the way, because it's a Rare Breed (fuck Rare Breed). Originally Posted By ELittlefield: Originally Posted By shultz: Originally Posted By ELittlefield: It sticks out a tiny bit. Still closes up though. I haven't shot this yet. [url]https://i.imgur.com/zg1PO1D.jpeg">https://i.imgur.com/zg1PO1D.jpeg">[url]https://i.imgur.com/zg1PO1D.jpeg Ok. Thanks for the tip. Shouldn't get in the way, because it's a Rare Breed (fuck Rare Breed). I think what @shultz meant is that the roll pin that holds the weight in the BCG is doing a lot more work if that weight is the only contact point the BCG assembly has with the sprung buffer. If it were a bit recessed, it would be the body of the BCG that interfaces with the sprung buffer instead (which it's designed to do, and is typical where that weight is absent, e.g., in an AR). You want the roll pin's job to be limited to keeping that weight in place inside the BCG, rather than also stopping the sprung buffer from moving forward. |
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Originally Posted By lugnutwrench2: I think what @shultz meant is that the roll pin that holds the weight in the BCG is doing a lot more work if that weight is the only contact point the BCG assembly has with the sprung buffer. If it were a bit recessed, it would be the body of the BCG that interfaces with the sprung buffer instead (which it's designed to do, and is typical where that weight is absent, e.g., in an AR). You want the roll pin's job to be limited to keeping that weight in place inside the BCG, rather than also stopping the sprung buffer from moving forward. Originally Posted By lugnutwrench2: Originally Posted By ELittlefield: Originally Posted By shultz: Originally Posted By ELittlefield: It sticks out a tiny bit. Still closes up though. I haven't shot this yet. [url]https://i.imgur.com/zg1PO1D.jpeg">https://i.imgur.com/zg1PO1D.jpeg">[url]https://i.imgur.com/zg1PO1D.jpeg Ok. Thanks for the tip. Shouldn't get in the way, because it's a Rare Breed (fuck Rare Breed). I think what @shultz meant is that the roll pin that holds the weight in the BCG is doing a lot more work if that weight is the only contact point the BCG assembly has with the sprung buffer. If it were a bit recessed, it would be the body of the BCG that interfaces with the sprung buffer instead (which it's designed to do, and is typical where that weight is absent, e.g., in an AR). You want the roll pin's job to be limited to keeping that weight in place inside the BCG, rather than also stopping the sprung buffer from moving forward. Yessir. What I meant is that since the Rare Breed does not require a cut weight, flipping it around is still compatible with FRT mode. Attached File Attached File |
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Originally Posted By ELittlefield: Yessir. What I meant is that since the Rare Breed does not require a cut weight, flipping it around is still compatible with FRT mode. https://www.ar15.com/media/mediaFiles/590787/IMG_3249_jpeg-3712596.JPG https://www.ar15.com/media/mediaFiles/590787/IMG_3250_jpeg-3712597.JPG Ah! Gotcha. Apologies for not connecting the dots. 
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I'm considering the same thing. I'm probably going to get the cmmg banshee 8". It seems like a system that requires less tinkering to get it running with an frt (Partisan). I'll probably buy the complete glock banshee and then also use a regular AR frt lower and use cmmg's conversion mags. I'm still doing research, though so time will tell. . |
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Originally Posted By mini14jac: I bought a FM9 specifically to run a Super Safety in. I modified the bolt, ground away the little shelf in the upper, and tried 3 or 4 different buffers and springs. Never got it to work in Super Safety mode. Bought a Lee lower for a MP5K clone and it purrs like kitten. @mini14jac Depending on when your FM9 bcg was made, it may have the weak firing pin spring that wont run with an frt device. You get live round/dead trigger issues with all buffer weights due to the firing pin spring The amazon replacement spring is like $5 for a 3 pack. reddit discussion about fm9 firing pin spring |
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Originally Posted By NWRed: @mini14jac Depending on when your FM9 bcg was made, it may have the weak firing pin spring that wont run with an frt device. You get live round/dead trigger issues with all buffer weights due to the firing pin spring The amazon replacement spring is like $5 for a 3 pack. reddit discussion about fm9 firing pin spring You may be right. I think it was in 2024, but I’m not sure. |
| If the KAK tungsten weight fits your bolt, it should allow you to reach minimum safe weight (22oz) using only an H3 buffer, with the potential advantage of more buffer weight range of motion to tame bolt bounce. That’s how my blowback 9mm SBR with 10” barrel works using an Arizona Regulator 2-position FRT. |
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I finally moved the RB FRT out of the Copperhead-K and put it in my stunt AR9 SBR. I don’t know what it is about FRTs but as usual for me the first box was single and double shots with a dead triggers between but by the second box things ran great. Maybe things needed to settle in? It was well lubed. The surprising thing is that this little 4.5” blowback AR is much more pleasant to shoot than was the MPX, I didn’t expect that. Even five and ten round bursts were controllable due to reduced muzzle rise. I have several uppers, this is a newer cheap one that happened to be on the rifle. Quarter Circle 10 Colt pattern lower, RB 3P FRT with Datum sleeved pins and modified FCD selector, Pro2A 5” complete upper with their BCG, LWRCI UCIW stock with HeavyBuffers U9 buffer and their recoil spring. Attached File |
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Originally Posted By heavyduty: I finally moved the RB FRT out of the Copperhead-K and put it in my stunt AR9 SBR. I don’t know what it is about FRTs but as usual for me the first box was single and double shots with a dead triggers between but by the second box things ran great. Maybe things needed to settle in? It was well lubed. The surprising thing is that this little 4.5” blowback AR is much more pleasant to shoot than was the MPX, I didn’t expect that. Even five and ten round bursts were controllable due to reduced muzzle rise. I have several uppers, this is a newer cheap one that happened to be on the rifle. Quarter Circle 10 Colt pattern lower, RB 3P FRT with Datum sleeved pins and modified FCD selector, Pro2A 5” complete upper with their BCG, LWRCI UCIW stock with HeavyBuffers U9 buffer and their recoil spring. https://www.ar15.com/media/mediaFiles/18/IMG_3941_jpeg-3738666.JPG damn, that's just a classy and clean little setup. |
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I had it out again today, this time with a suppressor (a R9.) I was getting about 5% dead trigger and that rate seemed to increase as the gun got dirtier. I’ll clean and try again. My BCG and buffer weigh a total of 24 oz, so I don’t think it’s bolt bounce. Ammunition was 124 gr Blazer brass. I think I saw someone write about a dry lube that worked well in these FRTs. Does that ring any bells? |
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This is annoying. I put together an alternate upper using a 8.3” BA barrel and my old CQ10 BCG, it runs fine in semi but I only got two short FRT bursts in 100 rounds. I’m going to try again using the same BCG as I’ve been using in my other upper but I am trying to figure out how to approach diagnosing the issue. My symptom is a dead trigger after the first shot in spicy mode. Both BCGs are FA cut and BCG + buffer weight is in the 24oz range. The buffer is a HeavyBuffers U9 which has freely sliding weights and the FRT is a RB 3P. There are no marks on the bolt weight so I don’t think it needs to be relieved. With 24oz I’m doubting bolt bounce is an issue. Could it be tolerance stacking not allowing the locking bar to be fully depressed? I should see if the bolt can be pushed forward the next time this happens, maybe I’m right on the ragged edge of depressing the locking bar enough. Could it be hammer follow? Attached File |
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You might try looking at the firing pin spring. FoxtrotMike bcgs wouldnt work with frts until someone figured out the firing pin was weak and was allowing the firing pin to be in wrong position when the hammer landed. Using a heavier spring fixed the issue. From Blowback9s website https://blowback9.wordpress.com/2025/08/03/sscs/9mm blowback – Light primer strikes (light strikes, dead trigger, hammer follow) not solved with deadblow buffer: The root cause of this problem is often when the bolt hits the breech face (closes), the firing pin continues moving forward under momentum. If the firing pin spring cannot get the firing pin back in place at the rear of the FP channel in time for the next hammer blow, a light strike results. There are 4 fixes: Lighter firing pin Stronger firing pin spring No XP/.308 springs! No Rifle-length springs either. Standard carbine or reduced power buffer spring Try replacing the disconnector (no idea why this works, but it has fixed this issue). Many people experiencing light strikes, especially with Foxtrot Mike bolts, have reported success by using a Delta Team Tactical (Recoil Technologies) Titanium Firing Pin. Many people report replacing the firing pin spring with a stronger spring resolves light strikes in a variety of different bolts. This is the current one that seems to work for many bolts: Uxcell 5mm OD, 0.5mm Wire Size, 25mm Free Length Spring. This spring will work in Foxtrot Mike bolts, but Foxtrot Mike is also now making their own stronger FP spring, and report that their new bolts should come with the new spring. More details below. Use a standard or lightweight carbine strength buffer spring. For a FRT or SS builds I use a Tubb Lightweight 300BO (ARBUFLW) spring to reduce the rate of fire (cyclic rate). It works fine with 11oz. OR MORE in the buffer tube. A Sprinco Yellow (25113), Wolff Reduced Power (16502), or Nemo Arms 300BO spring (300BLK-S) would be good choices as well. NEVER use an XP spring, .308 spring, or Rifle length spring. A stronger spring thrusts the bolt forward too fast, causing the firing pin to fly forward in the channel under momentum when the bolt stops. If he firing pin spring can’t get the firing pin back into position in time for the next hammer blow, the result is a light strike. Foxtrot Mike bolts previously included a very light firing pin spring. As of Dec. 2025, Foxtrot Mike is now making their own stronger FP spring, and report that their new bolts should come with the new spring. Since the bolt weight doesn’t need to be trimmed in FM bolts, this means that the FM bolt may be the best drop-in option for 9mm Super Safeties. Note that this bolt only works with lowers that have a forward angled ejector, NOT 90 deg. ejectors like Spikes, R&D Precision Colt Mag Adapters, or Colt lowers. Advertisement |
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| I have measured multiple QC10 bolts as a few thou short in the trip area vs Colt 9mm SMG bolts. If you have shims, stack some over the barrel extension so barrel is pushed a few thou forward so it allows the bolt to come a few thou forward to trip the lever. |
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Originally Posted By NWRed: You might try looking at the firing pin spring. FoxtrotMike bcgs wouldnt work with frts until someone figured out the firing pin was weak and was allowing the firing pin to be in wrong position when the hammer landed. Using a heavier spring fixed the issue. From Blowback9s website https://blowback9.wordpress.com/2025/08/03/sscs/9mm blowback – Light primer strikes (light strikes, dead trigger, hammer follow) not solved with deadblow buffer: The root cause of this problem is often when the bolt hits the breech face (closes), the firing pin continues moving forward under momentum. If the firing pin spring cannot get the firing pin back in place at the rear of the FP channel in time for the next hammer blow, a light strike results. There are 4 fixes: Lighter firing pin Stronger firing pin spring No XP/.308 springs! No Rifle-length springs either. Standard carbine or reduced power buffer spring Try replacing the disconnector (no idea why this works, but it has fixed this issue). Many people experiencing light strikes, especially with Foxtrot Mike bolts, have reported success by using a Delta Team Tactical (Recoil Technologies) Titanium Firing Pin. Many people report replacing the firing pin spring with a stronger spring resolves light strikes in a variety of different bolts. This is the current one that seems to work for many bolts: Uxcell 5mm OD, 0.5mm Wire Size, 25mm Free Length Spring. This spring will work in Foxtrot Mike bolts, but Foxtrot Mike is also now making their own stronger FP spring, and report that their new bolts should come with the new spring. More details below. Use a standard or lightweight carbine strength buffer spring. For a FRT or SS builds I use a Tubb Lightweight 300BO (ARBUFLW) spring to reduce the rate of fire (cyclic rate). It works fine with 11oz. OR MORE in the buffer tube. A Sprinco Yellow (25113), Wolff Reduced Power (16502), or Nemo Arms 300BO spring (300BLK-S) would be good choices as well. NEVER use an XP spring, .308 spring, or Rifle length spring. A stronger spring thrusts the bolt forward too fast, causing the firing pin to fly forward in the channel under momentum when the bolt stops. If he firing pin spring can’t get the firing pin back into position in time for the next hammer blow, the result is a light strike. Foxtrot Mike bolts previously included a very light firing pin spring. As of Dec. 2025, Foxtrot Mike is now making their own stronger FP spring, and report that their new bolts should come with the new spring. Since the bolt weight doesn’t need to be trimmed in FM bolts, this means that the FM bolt may be the best drop-in option for 9mm Super Safeties. Note that this bolt only works with lowers that have a forward angled ejector, NOT 90 deg. ejectors like Spikes, R&D Precision Colt Mag Adapters, or Colt lowers. Advertisement Good info - thanks! None of my BCGs are FM but swapping out the firing pin springs sounds like it would be a good thing to try. The recoil spring is specific to the LWRCI RE, and the disconnector doesn’t apply here (RB.) |
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Originally Posted By MickB: I have measured multiple QC10 bolts as a few thou short in the trip area vs Colt 9mm SMG bolts. If you have shims, stack some over the barrel extension so barrel is pushed a few thou forward so it allows the bolt to come a few thou forward to trip the lever. I never would have thought of that. I’ll try to track down some shims - thanks! |
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Originally Posted By heavyduty: I never would have thought of that. I’ll try to track down some shims - thanks! Originally Posted By heavyduty: Originally Posted By MickB: I have measured multiple QC10 bolts as a few thou short in the trip area vs Colt 9mm SMG bolts. If you have shims, stack some over the barrel extension so barrel is pushed a few thou forward so it allows the bolt to come a few thou forward to trip the lever. I never would have thought of that. I’ll try to track down some shims - thanks! Some AR handguards come with shims to enable proper indexing. Instead of putting the shims on the front side of the barrel extension, cut a small section out of the shim to clear the index pin and stack them on the back of the barrel extension. |
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Originally Posted By MickB: Some AR handguards come with shims to enable proper indexing. Instead of putting the shims on the front side of the barrel extension, cut a small section out of the shim to clear the index pin and stack them on the back of the barrel extension. Brownells has an inexpensive pack of handguard shims that I ordered. Is there a suggested measurement I’m looking to hit, like from breech to takedown pin or something standardized? I also have some of the heavier firing pin springs mentioned above coming. |
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I just posted about my foxtrot mike 9 in another thread. Works great. I took out the weight due to need to have a law tactical extension plug and then run a 10oz buffer from kaw valley and it just ran right with a hoffman super safety right from the get go. Eta i have the rear charging NOT the side. |
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Originally Posted By bionicmonkey: I just posted about my foxtrot mike 9 in another thread. Works great. I took out the weight due to need to have a law tactical extension plug and then run a 10oz buffer from kaw valley and it just ran right with a hoffman super safety right from the get go. Eta i have the rear charging NOT the side. If you want to play with slowing down ROF. You should be able to trim the weight to work with both a SS and the LAW folder. |
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I spent some time at the range today with the 8.3” upper on the AR9. It’s coming along but isn’t quite there yet. @MickB hit it - the QC10 bolt measures 0.004” shorter than my other BCG and refuses to run spicy. I put a heavier firing pin spring in the other BCG and took several types of ammunition with me this time. No luck with WWB 115s or Blazer Brass 115s, not much better with Blazer Brass 124s but Lawman 124s ran about 75% of the time. I think I’m going to try shimming the barrel forward a bit and see what happens. I really like how this longer upper shoots - I’ll try and do comparison measurements against the short upper to see if there is a difference. |
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Not much of a data point, but my FM upper purchased perhaps five years ago runs flawlessly with the Partisan. Have only fired it 100 rounds or so, but no issues. It has the weight in the back of the bolt, into which I bored a hole so that it would accommodate the bolt extension for a Law Tactical folding stock adaptor. I'm probably going to part with this upper though, as I don't like not having a built in ejector. The Endomags have never stuttered, but the built in ejector nub makes me uncomfortable, and I'd just prefer a Colt magazine compatible upper. 
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Originally Posted By Glocked: If you want to play with slowing down ROF. You should be able to trim the weight to work with both a SS and the LAW folder. Originally Posted By Glocked: Originally Posted By bionicmonkey: I just posted about my foxtrot mike 9 in another thread. Works great. I took out the weight due to need to have a law tactical extension plug and then run a 10oz buffer from kaw valley and it just ran right with a hoffman super safety right from the get go. Eta i have the rear charging NOT the side. If you want to play with slowing down ROF. You should be able to trim the weight to work with both a SS and the LAW folder. yes, that should be possible. if others are interested i'm happy to see about measuring where the FM pin is relative to the plug etc.. for me, I am actually going to try the other way and try it with the kak lightweight law extension to increase the ROF. |
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I took MickB’s suggestion above to shim the barrel forward a bit, I started with seven thou. Things are running much better, but when it comes to FRT operation it’s definitely ammunition sensitive. It doesn’t like Blazer Brass 124 or any 115 I’ve tried, I get the most success with Lawman 124. I’m going to try some hotter Winchester Q4318 124 to see if it makes a difference. I’m also wondering if a lighter firing pin is worth trying. Any suggestions for a source? Are 9mm AR firing pins the same as 5.56? I already installed the heavier firing pin spring suggested above. |
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Originally Posted By heavyduty: Finally got back to the range today after installing a titanium firing pin and grabbing some Q4318. It ran perfectly, 100 spicy rounds without any issues at all. I think I found the right combination. Thanks for all the help, people! Cool! Now try to get it to feed hollow points.
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| Installed a Partisan Disruptor in my AR9 tonight. Did a test run and semi function was perfect but in the 3rd position the trigger would not reset. BCG/buffer weight are 23.3 oz however the buffer doesn't have sliding weights. Thoughts on what to change to get it running as well as it does in my .300BO? |
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Originally Posted By leemozoid: Installed a Partisan Disruptor in my AR9 tonight. Did a test run and semi function was perfect but in the 3rd position the trigger would not reset. BCG/buffer weight are 23.3 oz however the buffer doesn't have sliding weights. Thoughts on what to change to get it running as well as it does in my .300BO? So, the solid buffer runs your 300? That'd be surprising. I think the buffer is the obvious candidate for your stoppage. How did you determine it was not reseting? Can you describe the specific details of your stoppage? Hammer charged or hammer down? Failure to reset would indicate 2nd and 3rd position are performing identically. Is this actually what you are finding? |
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Originally Posted By leemozoid: Installed a Partisan Disruptor in my AR9 tonight. Did a test run and semi function was perfect but in the 3rd position the trigger would not reset. BCG/buffer weight are 23.3 oz however the buffer doesn't have sliding weights. Thoughts on what to change to get it running as well as it does in my .300BO? Can you be a little more detailed when you say the trigger does not reset? You're in FRT mode, you pull the trigger and a round fires, what is the state of the gun now? Is a round chambered? Is the hammer forward? Anything else we should know? I'm going to be recommending the KVP 10 ounce buffer, with 4 tungsten sliding weights, but I want to make sure I understand your malfunction. https://www.joeboboutfitters.com/Kaw-Valley-Precision-Tungsten-Blowback-Buffer-10oz-p/kvp-buffer-10oz.htm |
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Originally Posted By carholio: I'm considering the same thing. I'm probably going to get the cmmg banshee 8". It seems like a system that requires less tinkering to get it running with an frt (Partisan). I'll probably buy the complete glock banshee and then also use a regular AR frt lower and use cmmg's conversion mags. I'm still doing research, though so time will tell. .  You can have a configuration like below that has low reciprocating mass and a low cyclic rate: With straight blowback you looking at about double the mass I have below.  |
FRT optimized 9mm AR? (Page 1 of 2)
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