Need Advice SBR'ing my PS90

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  • Patrick

    MSI Executive Member
    Apr 26, 2009
    7,725
    Calvert County
    Already got the Form 1 back, so good to go on the NFA front. This is purely a technical post.

    I need to figure out the "best" way to go about this. I have the 16" PS90 from FN sitting here and love shooting this gun. I think I'll like it more as an SBR.

    My questions to the jury:

    - Should I send my 16" barrel to CMMG for a cut and re-thread to about 12" so that it can support my Blackout flash-hider and SCAR-H SD suppressor? This is a silencer that actually wraps back behind the muzzle, so it needs a longer barrel.

    - Or, should I just go to the standard P90 10.3" barrel, get a 1/2x28 adapter and wait for the money to get a new suppressor that will sit in front of the muzzle?

    - And if so, should I buy a new barrel or ask CMMG to cut it down for me? It's cheaper but I lose the 16" barrel. But swapping them out is not a 10-minute job so it's not likely I am going back to 16". Maybe not a loss. And I could use the saved dollars to get something else.

    - And I guess the obvious question: does a suppressor on a PS90 even make a difference?

    - If I buy a new barrel, what twist is best for a 10.3" length and the standard 40 grn. V-Max 5.7 round? CMMG offers 1/7 and 1/9. I generally prefer tighter twists, but this is not scientific reasoning by me. It's just something that seems to make sense. But I might be wrong.

    - And finally, how much work to do this myself? I've seen the online guides for it but am curious how easy it is to screw up.

    That's a lot of questions for one post. Thanks in advance for any input.
     

    SCARCQB

    Get Opp my rawn, Plick!
    Jun 25, 2008
    13,614
    Undisclosed location
    Congratulations of your new toy. I have one and it iswell worth the wait and effort.

    There are many routes you can take to get this project completed. IMHO, the main factor that will affect your decision is the ability for you to use the ps90 sbr with the SCAR SD suppressor.

    You can use this can with your set-up. however, the eccentric barrel lenght requirements of that can ( telescoped interface) will require some customized gunsmithing to get it to work. Current adapters that are readily available are too short.
    Cutting the existing barrel will also expose the pencil thin barrel that is under the barrel sleeve.This may result in a big gap between the adapter and the barrel itself. That detriment is simply cosmetic and should not affect performance. Installing the appropriate AAC adapter in cover that gap.

    Cutting the original Chrome lines barrel may also result in flaking at the muzzle after a while. Some people have experienced this. I have not. A new P-90 barrel is the best option. It is simple to install with slightly modded wrenches. An adapter is usually required to for cans in 1/2x28tpi threads. Most over the counter barrels and adapters will not work with your SCAR SD can. If you want to use this can, you need a custom job, common SBR mods. you may have to buy another can that sits in fron of the muzzle instead of over it.

    As for suppressing the PS90 SBR... The diffrence is not that great. It still sounds like an unsuppressed 22 short due to the 40 grain Vmax still breaking the sound barrier. But definite quieter if compared to an unsuppressed vesrion or a 10.5" AR sbr. Bystanders notice a more reduced sound signature, the firer does experience a slightly louder report due to closer proxity of the ear to the muzzle/ breech, typical of bullpup designs.

    I have suppressed my PS90 not because of sound reduction, but mostly for muzzle control. The suppressor acts as a barrel weight, effectively reducing recoil, muzzle blast and allows you to stay on target. This allows for rapid delivery of accurate shots. A suppressed PS90 almost feels like you are firing a Ruger 10/22 in bullpup configuration.

    In fact, My PS90 and PS90 SBR is my favorite CQB carbine at this point. It has replaced my Colt AR as my primary HD weapon.

    barrels/ .5x28tpi adapters can be obtained from :
    highdessertdog
    CMMG

    barrel cutting / SBR conversions can be done by:
    TROS
    HDPS
    Highdessertdog

    Just my two cents. I hope this helps

    scar

    Below:
    (L)PS90 SBR with AAC SCAR HD QD mount. ( picture was photochopped:D)
    (R) PS90 SBR with AAC 51T 1/2x28 Adapter for use with M42000 suppressor
     

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    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Per Bob Ailes (FNH Rep), the CMMG Barrels have a very high rate of problems, especially with Suppressed Platforms. Aparently they dont chrome line the chambers whick leads to extraction issues. SOme PS90's need bolt weights when using certain ammo (Bolt is too light)

    Best bet is to chop the 16" barrel off with a hack saw @ 13" and the barrel will slide out. Send it to TROS USA.

    Im waiting for a F1 on my PS90, and I will be threading my own barrel at the shop, but TROS would be who I use if I couldnt thread my own. Im using a SWR Spectre on my PS90 and 5.7 (The 5.7 is done and threaded, very quiet)
     

    boatbiologist

    Active Member
    Nov 6, 2008
    612
    Glen Burnie
    Thought about putting my M4-1000 on my PS90 before. Only real way is to SBR it, 1/2 x 28 adapter to AAC flashhider. Also, I really like the look of the P90 slanted flashhider and not the AAC Phantom on it. This is the first I heard of CMMG barrel issues- good to know.

    As SCAR said, you will get a sonic crack so it won't suppress good enough for my needs anyway. Guess that is why I never got around to it.

    Congrats on the Form 1. If it were me, I would stay as close to the P90 look as possible and forget about suppressing it unless I went with something that would work the the P90 style flash hider like Gemtech has.
     

    SCARCQB

    Get Opp my rawn, Plick!
    Jun 25, 2008
    13,614
    Undisclosed location
    Another factor to consider when suppressing the PS90 SBR is chamber pressure. These guns run on a straight blowback principle. Suppressors that are highly efficient ( mostly 5.56 cans) can often lead to pressure build-up in the chamber causing the brass to expand longer. This can throw the extraction timing off. This situation can lead to extraction issues.

    I'm currently using an AAC M42000 and a couple of 9mm cans for my SBR. These seem to work well, but the sonic crack is still loud. Subsonic loads take care of this but those are a bit too pricey.
     

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    Patrick

    MSI Executive Member
    Apr 26, 2009
    7,725
    Calvert County
    Great info, as expected. Thanks.

    Thinking it over with all of the above advice, I agree that extending the profile with a long flash hider ala SCAR-H SD is kinda dumb. That photochop clinched it. ;)

    So I'll knock it down to the P90 length (or thereabouts).

    Also this is the first I've heard of issues with CMMG barrels, so good to know from a good source. Thanks.

    I see no reason to keep a 16" barrel around for a gun that does not do easy swaps. With the addition of Clandestine's words, chopping and sending to TROS is the way I'll go plus an adapter and an eventual can of some other flavor. Until then I have an A2 FH from my pre-suppressed LWRC I can use.

    I was going to try a Sparrow .22 and had not considered it for the PS90 because I wanted a quick-detach. But maybe it won't matter. Also will look at the SWR. The pistol suppressors are much lighter and frankly it was a dumb idea to put something as heavy as a full size 7.62 can on a 5.7. That was just me being cheap and/or not thinking it through.
     

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