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Posted: 7/5/2025 2:02:50 PM EDT
| I'm working on a PS90 SBR and I need to choose a QD silencer mount. CMMG makes an adapter that changes their PS90 SBR barrel's M12x1.0 LH threads to standard 1/2x28. Then I could put another muzzle device on the adapter, but if possible I'd prefer to just have the QD silencer mount directly attach to the barrel without an adapter in between. However the only thing I've found that does that is JMAC's Keymicro mount, and I don't particularly care for Keymo/Keymicro. Does anyone know of any other PS90 silencer mounts that attach directly to the CMMG SBR barrel's M12x1.0 LH threads? |
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I don’t believe you can actually thread a suppressor directly onto the barrel on a PS90, if that’s what the OP is talking about. It needs the adapter/muzzle device on the end of the barrel because that’s what holds the barrel in place. The barrel is inserted from the rear and then the adapter/muzzle device is screwed onto the barrel threads, which also traps a spring that allows slight fore-aft movement needed as part of the recoil system. Any adapter/muzzle device needs to have the same shape as the factory comp since it has to fir under the overhang at the front of the receiver. While some people do have the factory barrel cut and threaded, I haven’t heard of anyone threading it to 1/2x28. You still need to have a muzzle device on the end, and as far as I know they are all threaded M12x1 to mate with the factory barrel threading. |
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Originally Posted By willi3d: I don’t believe you can actually thread a suppressor directly onto the barrel on a PS90, if that’s what the OP is talking about. No it's not what I was talking about. I don't want to go barrel threads -> M12x1.0 LH to 1/2x28 adapter -> QD adapter -> silencer. I want to go barrel threads -> QD adapter -> silencer. |
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Originally Posted By willi3d: I don’t believe you can actually thread a suppressor directly onto the barrel on a PS90, if that’s what the OP is talking about. It needs the adapter/muzzle device on the end of the barrel because that’s what holds the barrel in place. The barrel is inserted from the rear and then the adapter/muzzle device is screwed onto the barrel threads, which also traps a spring that allows slight fore-aft movement needed as part of the recoil system. Any adapter/muzzle device needs to have the same shape as the factory comp since it has to fir under the overhang at the front of the receiver. While some people do have the factory barrel cut and threaded, I haven’t heard of anyone threading it to 1/2x28. You still need to have a muzzle device on the end, and as far as I know they are all threaded M12x1 to mate with the factory barrel threading. I had mine cut and threaded to 1/2 x 28 by TROS 10 years ago, |
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Originally Posted By MikeSearson: I had mine cut and threaded to 1/2 x 28 by TROS 10 years ago, OP, just use an adapter nut like 99% of people did, with your preferred QD mount. It’ll be fine. |
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TROS makes a tri lug mount specifically for the PS90 that threads directly onto the barrel but good luck getting ahold of them to actually make one for you. I’m using the CMMG adapter and the HBI tri lug mount that has the ports. Be aware that some CMMG adapters are threaded poorly and don’t mount concentrically with the barrel. They seem to be good about replacing bad parts though. |
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As mentioned Gemtech made a bi-lug mount that came with their SP90 suppressor. In my experience it wasn’t that great, the alignment rod was always just a gnats ass from touching the end of the suppressor. I tried it with multiple barrels and same result every time. Tried rebuilding the mount and doing various things to make it true up with no success. Gemtech wasn’t any help, talked with Greg at GSL and could send the suppressor/mount to them but that seemed like a lot of hassle. Shooting I did not get any noticeable baffle strikes but it did throw the POI off more than a foot and something just wasn’t right. In the end I bought a some various bits from Griffin and Ecco and cobbled together my own mount system that is direct thread to a CMMG threaded mount. It’s not quick disconnect anymore but the alignment rod is now true and straight down the middle of the SP90 and there is almost no POI change with/without it. Frankly the Gemtech Bi-lock design for it is junk in my experience and I wouldn’t recommend even bothering to hunt it down. I would just sell the thing along with the end cap it mounts to but the SP90 is a pretty rare can and although I don’t have use for it I hate to separate it. The SP90 is a cool and unique piece but it’s pretty long, about the same installed as a factory PS90 is. Funny enough Gemtech apparently licensed for a dummy suppressor with their name on it that fits over a PS90 barrel shroud. It looks the part from more than a few feet away. Best way to suppress a P90 in my experience is to just accept that it’s not gonna be all that quiet and get a cheap short/fat can like a YHM R9 that will knock the edge off but not create too much back pressure. Just use a CMMG muzzle device and direct threat it on or use a quick disconnect fromn whatever brand of can you pick if that matters to you. |
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Originally Posted By willi3d: You have very limited options since hardly anyone makes a suppressor muzzle device in that unique thread pitch. You can buy the B&T suppressor that attaches to the standard PS90 flash hider/comp. |
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Originally Posted By aksahsalahs: GSL/Gemtech used to make one. But not sure if the still do. I'd just use the CMMG 1/2x28 adapter. Its what I have and works great. I have a Plan B muzzle device on there. I have a Gemtech SP90 and never could get the can to align correctly using the Gemtech bi-lock mount. It wasn’t enough to cause a full up baffle strike but I think the bullets were maybe lightly grazing something on the way out. POI change was over a foot at 25 yards when I put the can on. After a lot of messing around trying to make the Gemtech Bi lock work I gave up. Turns out Griffin armament makes direct thread mount thing for one of their pistol cans that could replace the Bi-lock mount assembly. Use a CMMG muzzle device that is then 1/2x28 to attach a can. Can lined up perfectly once I got that figured out and nearly zero POI change when I put the can on. It’s not quick disconnect but it works now and that’s what matters. The SP90 cans are pretty hard to get so I’m glad it’s usable. |
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Originally Posted By CleverNickname: FWIW I ended up going with a YHM Fat Cat, since it has a short QD mount and the can itself is short. No point to going with a long can when you have a short gun. I know it's an old thread, but how is it working out? PSA is having a sale on PS90s and I've got one on the way, after years of dancing around it  Now to find mags and a barrel... @CleverNickname |
"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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Originally Posted By Evil_Ed: I know it's an old thread, but how is it working out? PSA is having a sale on PS90s and I've got one on the way, after years of dancing around it Now to find mags and a barrel... @CleverNickname I'm not very happy with it. The PS90's accuracy isn't all that great already (I'm assuming because the barrel can move and twist a little inside the receiver instead of being fixed?). I zero'ed the gun with a new optic last Saturday and it's definitely worse with the Fat Cat installed. I'm thinking of just removing the SRX mount and going unsuppressed using the factory flash hider. And yes, I double-checked and I don't see any signs of baffle strikes. |
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Originally Posted By CleverNickname: I'm not very happy with it. The PS90's accuracy isn't all that great already (I'm assuming because the barrel can move and twist a little inside the receiver instead of being fixed?). I zero'ed the gun with a new optic last Saturday and it's definitely worse with the Fat Cat installed. I'm thinking of just removing the SRX mount and going unsuppressed using the factory flash hider. And yes, I double-checked and I don't see any signs of baffle strikes. |
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Originally Posted By Buffman_LT1: What adapter are you using to go from the barrel to the SRX? one of the CMMG M12 to 1/2? Those are known to have problems, specifically alignment issues. Originally Posted By Buffman_LT1: Originally Posted By CleverNickname: I'm not very happy with it. The PS90's accuracy isn't all that great already (I'm assuming because the barrel can move and twist a little inside the receiver instead of being fixed?). I zero'ed the gun with a new optic last Saturday and it's definitely worse with the Fat Cat installed. I'm thinking of just removing the SRX mount and going unsuppressed using the factory flash hider. And yes, I double-checked and I don't see any signs of baffle strikes. Yes, the CMMG adapter on a CMMG 10.3" barrel. |
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I had my barrel cut and threaded 1/2x28 so I could use a 5.56mm Gemtech bilock muzzle device back before Plan B was a thing FN PS 90 Adapter | Gemtech ETA: It's possible it's a PS90 bilock - it's been 15 years - Henderson Defense cut my barrel and I put on the mount. I'm positive it's a 5.56mm bilock but... My first suppressor was a Gemtech G5 and I put their 5.56 bilock flash suppressors on several carbines. |
Et quant au repos ? Le Caliphate doit être essuyé de la terre.
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Originally Posted By CleverNickname: I'm not very happy with it. The PS90's accuracy isn't all that great already (I'm assuming because the barrel can move and twist a little inside the receiver instead of being fixed?). I zero'ed the gun with a new optic last Saturday and it's definitely worse with the Fat Cat installed. I'm thinking of just removing the SRX mount and going unsuppressed using the factory flash hider. And yes, I double-checked and I don't see any signs of baffle strikes. OEM barrel cut and threaded. Gemtech bilock 5.56mm (99% sure) mount . Old school Gemtech G5 suppressor. It's possible it's a PS90 bilock - it's been 15 years - Henderson Defense cut my barrel and I put on the mount. I think your tolerance stack is stacking up. |
Et quant au repos ? Le Caliphate doit être essuyé de la terre.
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Originally Posted By ODA_564: I think your tolerance stack is stacking up. I agree. And that's the whole reason I posted this thread in the first place, to try to avoid that possibility!  I ordered a PS90 flash hider yesterday. Now I just have to remove the thread adapter and SRX mount that I Rocksett onto the barrel. |
| I was looking for a different PS90 part and I noticed JMAC has now has a M12x1 LH thread to 1.375x24 Hub thread converter/muzzle brake, which is pretty much exactly what I was looking for when I started this thread. It must be an FN Specialties exclusive, because it's not on JMAC's site. I'll probably buy one next month to try out. |
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They’re on JMac’s web site…just forever out of stock I’ve been looking at either that or their Keymo mount…if I was going to %100 dedicate a can JUST to the PS90 then the Hub mount would be the way to go for sure.
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"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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Originally Posted By CleverNickname: I was looking for a different PS90 part and I noticed JMAC has now has a M12x1 LH thread to 1.375x24 Hub thread converter/muzzle brake, which is pretty much exactly what I was looking for when I started this thread. It must be an FN Specialties exclusive, because it's not on JMAC's site. I'll probably buy one next month to try out. |
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Originally Posted By Buffman_LT1: I got one in and will let you know how it works out :D Originally Posted By Buffman_LT1: Originally Posted By CleverNickname: I was looking for a different PS90 part and I noticed JMAC has now has a M12x1 LH thread to 1.375x24 Hub thread converter/muzzle brake, which is pretty much exactly what I was looking for when I started this thread. It must be an FN Specialties exclusive, because it's not on JMAC's site. I'll probably buy one next month to try out. I just ordered one as well for the Polonium K I’m gonna use on mine; I’ll file the SBR paperwork probably once I’m sure the proposed rule change no longer requiring receiver marking goes into effect…then see how it all pans out. I was going to hold off and wait for the Keymo adapter to come into stock again but that might take months if not longer; JMac doesn’t exactly make huge runs of things.. |
"Oh, bother," said Pooh, as he pulled the pin on another grenade...
| My Form 1 came back in about 2 weeks on my PS90 I've had for a very long time lol. Since about 2016 or so, back when I prioritized which gun got a stamp and which could wait. I want to get it chopped down and threaded for a three-lug, mostly out of ease of use between other PCCs I've got. I'm thinking of a SilencerCo Spectre K, anyone ever go that route? Also, can the factory barrel be threaded easily for 1/2x28 three-lug mounts? I've got no reason to go with a CMMG barrel since I want to chop the factory barrel. |
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Originally Posted By Stonecutter6: My Form 1 came back in about 2 weeks on my PS90 I've had for a very long time lol. Since about 2016 or so, back when I prioritized which gun got a stamp and which could wait. I want to get it chopped down and threaded for a three-lug, mostly out of ease of use between other PCCs I've got. I'm thinking of a SilencerCo Spectre K, anyone ever go that route? Also, can the factory barrel be threaded easily for 1/2x28 three-lug mounts? I've got no reason to go with a CMMG barrel since I want to chop the factory barrel. Factory threads are 12x1 LH, there's not enough meat on the barrel to thread it 1/2x28. Barrel is less than .50 thick, so it can't happen. Per a SME on reddit, the CMMG barrel and more importantly the CMMG thread adapters have been known to not be threaded concentric with the bore...there's a decent chance a thread adapter will cause more problems than it solves. Personally I'd just embrace that it's a weird Euro thing, live with the 12x1LH threads, and buy an appropriate muzzle device in that thread and live with the limited can selection - unless you buy one of the Plan B adapters, the HUB adapter or the Keymo adapter that JMAC makes (and doesn't keep in stock...) |
"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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Originally Posted By CleverNickname: I was looking for a different PS90 part and I noticed JMAC has now has a M12x1 LH thread to 1.375x24 Hub thread converter/muzzle brake, which is pretty much exactly what I was looking for when I started this thread. It must be an FN Specialties exclusive, because it's not on JMAC's site. I'll probably buy one next month to try out. I installed one of these adapters on my PS90 and Fat Cat and now the accuracy suppressed is just the same as unsuppressed. I'm almost certain the accuracy problems that I was having before were due to tolerance stacking. |
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Nice - I got one in, at about the same time as my Form 1 cleared…I haven’t actually made the SBR yet though - half laziness, half hoping the final ruling comes through and they drop marking on SBRs so I can just cut the barrel off and make the SBR without marking it I’ve got a Polo K and the adapter ready to go though…maybe I should just strip the thing and send it off for marking next week anyway, bleh…
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"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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