Advice on sbr

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  • outrider58

    Pronouns: It, That
    MDS Supporter
    Jul 29, 2014
    37,491
    Word is NC is turning into east CA

    Yeah. That was our first choice a couple years ago. It's down near the bottom of our list now and if we did go there, it would be the western side, the hell away from the I95 corridor.
     

    calicojack

    American Sporting Rifle
    MDS Supporter
    May 29, 2018
    3,743
    East Bumfkgypt
    The real argument for SBRs right now is that the ATF is hot to ban braced pistols, and thus they may not be a great long-term investment. Of course, if you want to go < 29" OAL, there's no other game in town.

    So I thought they were most interested in going after braced pistols in rifle calibers and that pistol calibers would still be pistols; but who knows for sure.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    12,851
    Rockville, MD
    So I thought they were most interested in going after braced pistols in rifle calibers and that pistol calibers would still be pistols; but who knows for sure.
    Their proposed criteria would be as rough on 9mm braced "pistols" as 5.56 braced "pistols". The only thing that would have made the pistol caliber guns score better would be not putting LPVOs and the like on them.
     

    outrider58

    Pronouns: It, That
    MDS Supporter
    Jul 29, 2014
    37,491
    So I thought they were most interested in going after braced pistols in rifle calibers and that pistol calibers would still be pistols; but who knows for sure.

    It is the brace that is evil. It makes guns more shootier.
     

    calicojack

    American Sporting Rifle
    MDS Supporter
    May 29, 2018
    3,743
    East Bumfkgypt
    Still taking orders. I received my last order fro them (RDB & Barrel) after about 7 months. It came two weeks ago.

    https://cmmg.com/barrel-and-bcg-kit-5-4140cm-sbn-9mm

    For an AR-9, best bang for the buck (no pun intended) is to build one of these CMMG rigs as a braced pistol (Outriders post above). The only thing is there are not many lower receivers that work with this barrel/bolt combo. The CMMG lowers are scarce. I have not done a 9mm CMMG RDB rig, but my understanding is that New Frontier Armory lowers work.

    For non-AR, The Ruger PC Carbines are pretty good value. They will accept Glock mags:
    https://ruger.com/products/pcCarbine/models.html

    And then there are the CZ, Beretta, and HK offerings already mentioned.
     

    rbird7282

    Active Member
    Dec 6, 2012
    13,904
    For an AR-9, best bang for the buck (no pun intended) is to build one of these CMMG rigs as a braced pistol (Outriders post above). The only thing is there are not many lower receivers that work with this barrel/bolt combo. The CMMG lowers are scarce. I have not done a 9mm CMMG RDB rig, but my understanding is that New Frontier Armory lowers work.

    For non-AR, The Ruger PC Carbines are pretty good value. They will accept Glock mags:
    https://ruger.com/products/pcCarbine/models.html

    And then there are the CZ, Beretta, and HK offerings already mentioned.


    You can always use a standard lower with Endomags with a CMMG bolt and barrel


    Sent from my iPhone using Tapatalk
     

    outrider58

    Pronouns: It, That
    MDS Supporter
    Jul 29, 2014
    37,491
    For an AR-9, best bang for the buck (no pun intended) is to build one of these CMMG rigs as a braced pistol (Outriders post above). The only thing is there are not many lower receivers that work with this barrel/bolt combo. The CMMG lowers are scarce. I have not done a 9mm CMMG RDB rig, but my understanding is that New Frontier Armory lowers work.

    For non-AR, The Ruger PC Carbines are pretty good value. They will accept Glock mags:
    https://ruger.com/products/pcCarbine/models.html

    And then there are the CZ, Beretta, and HK offerings already mentioned.

    Standard AR lowers(as rbird said), New Frontier, and with a slight bit of alteration on the feed ramps, QC5 & QC10, as well as most dedicated PCC lowers, etc. Mags that can be used, Colt, Glock, MP5, Endos including any existing Magpul standard AR mags with the Endo adapters.

    Some of the aforementioned lowers will not allow LRBHO, some will. A standard AR upper receiver is required for the RDB setup. You need the cam pin cutout.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    16,207
    PA
    For an AR-9, best bang for the buck (no pun intended) is to build one of these CMMG rigs as a braced pistol (Outriders post above). The only thing is there are not many lower receivers that work with this barrel/bolt combo. The CMMG lowers are scarce. I have not done a 9mm CMMG RDB rig, but my understanding is that New Frontier Armory lowers work.

    For non-AR, The Ruger PC Carbines are pretty good value. They will accept Glock mags:
    https://ruger.com/products/pcCarbine/models.html

    And then there are the CZ, Beretta, and HK offerings already mentioned.

    The more RDB builds I work on, the more I kinda don't like them. They are softer and smoother than blowback, but it's more of trying to adapt the AR design to 9mm than adapt 9mm to the AR platform. NFA and Aero EPC seem to work best for 3rd party, they need the ejector to be removed, and LRBHO (in the upper) won't work, in fact you can't use most PCC uppers, has to have the cam pin cutout, so rifle cal uppers are needed. Factory GLOCK mags sit a little higher than Magpul, so the Magpul tend to work better, factory mags usually catch the bolt lugs, and have to file down the mag catch so it sits lower. Problem is then it's kinda loose, and resting the mag on a table or so will jam or chew the mag. CMMG lowers are on perpetual backorder, but the feed angle being a little different and sitting just right are well worth it IMO.

    Or just build a blowback, use the 10oz KVP buffer, use a taccom BCG and Taccom or Macon armory barrel. They are dead reliable and will run mag after mag of HP ammo, anything from light loads to full +p with or without a can, and cuts down on gas in the face. Easy build simple operation, smooth and relatively light recoil, not far off of the RDB, but faster, simpler, and easire to get running. Use a short stroke kit and tough PCC rated trigger, and they really come alive, cuts the stroke down to a lighting fast 2" compared to 3" for most blowback, and 3.75" for rifle and RDB setups. Takes a lot of the slap, recoil, and sight movement out of the platform.

    Of course short stroke delayed blowback is king, and really the design that 9mm PCCs works best with. JP and a couple others have super expensive AR9s built around it, and more are on the way. There is also the Scheel roller delay buffer kit, will have one soon to play with, really hoping it runs well with a short stroke kit. Right now seems AR9s are popular enough to inspire new designs and seems most of the companies producing receiver sets now are working on delayed systems.


    For the OP's question, IMO 9mm really doesn't benefit much from barrels over 7", and shorter AR9s are a lot more fun, especially when suppressed. MD basically requires an 11" or greater 9mm barrel to be a "legal" SBR, so I would just stick with a brace and whatever barrel/suppressor muzzle device will clear your handguard of choice. Would definitely be a good candidate for a short barrel and pinned form 1 suppressor to get past the 29" length requirement.
     

    calicojack

    American Sporting Rifle
    MDS Supporter
    May 29, 2018
    3,743
    East Bumfkgypt
    Factory GLOCK mags sit a little higher than Magpul, so the Magpul tend to work better, factory mags usually catch the bolt lugs, and have to file down the mag catch so it sits lower. Problem is then it's kinda loose, and resting the mag on a table or so will jam or chew the mag.

    Oh boy did I find that out the hard way! Everything you said in spades!! When I tried a NFA lower on my RDB for 45 ACP (as opposed to 9mm), it did not work even after filing the release down to a nub. 45 APC seems to be worse than 9mm.

    OBTW - what is a short stroke kit?
     

    alucard0822

    For great Justice
    Oct 29, 2007
    16,207
    PA
    Oh boy did I find that out the hard way! Everything you said in spades!! When I tried a NFA lower on my RDB for 45 ACP (as opposed to 9mm), it did not work even after filing the release down to a nub. 45 APC seems to be worse than 9mm.

    OBTW - what is a short stroke kit?

    In PCC competition, people started adding spacers to the buffer tube shortening the bolt travel just behind where the trigger resets. Then using non-ramped bolts with the bottom shaped to cock the hammer faster, allowing even shorter bolt travel. The idea is that the shorter travel allows the action to cycle faster with proper bolt velocity, and less movement means less BCG inertia to slam into your shoulder or chamber, so less dot movement and usually less recoil. A 5.56 AR has a 3.75" stroke, most 9mm have a 3" stroke, and short stroke setups are about 2". Most 9mm bolts need a 3" travel for a LRBHO to work, but some, like the taccom or JP short stroke BCGs have a cutout to work with the shorter stroke.
     

    woodline

    Active Member
    MDS Supporter
    Jan 8, 2017
    1,888
    You can always use a standard lower with Endomags with a CMMG bolt and barrel


    Sent from my iPhone using Tapatalk
    OP is a lot better off doing RDB specific Endomags or waiting for a complete CMMG banshee to become available, otherwise he will likely end up making lots of ranty posts about parts compatibility. Specifically lack thereof.

    Here’s a fun website from a guy who has gotten certain builds running really well, and has had issues with others:

    https://c3junkie.com/?page_id=280

    The 9mm version is often called the “amphibian” build. He does a lot of experimentation, but basically recommends:

    CMMG BCG and barrel kit
    VLTOR A5 length buffer tube extension
    Kynshot RB5007 hydraulic buffer
    Tubb 5.56 flatwire spring
    RDB Endomags

    He’s got .40 s&w and .45acp versions up on his website now.
     

    outrider58

    Pronouns: It, That
    MDS Supporter
    Jul 29, 2014
    37,491
    OP is a lot better off doing RDB specific Endomags or waiting for a complete CMMG banshee to become available, otherwise he will likely end up making lots of ranty posts about parts compatibility. Specifically lack thereof.

    Here’s a fun website from a guy who has gotten certain builds running really well, and has had issues with others:

    https://c3junkie.com/?page_id=280

    The 9mm version is often called the “amphibian” build. He does a lot of experimentation, but basically recommends:

    CMMG BCG and barrel kit
    VLTOR A5 length buffer tube extension
    Kynshot RB5007 hydraulic buffer
    Tubb 5.56 flatwire spring
    RDB Endomags

    He’s got .40 s&w and .45acp versions up on his website now.

    Been reading his stuff. :thumbsup:
     

    rbird7282

    Active Member
    Dec 6, 2012
    13,904
    OP is a lot better off doing RDB specific Endomags or waiting for a complete CMMG banshee to become available, otherwise he will likely end up making lots of ranty posts about parts compatibility. Specifically lack thereof.

    Here’s a fun website from a guy who has gotten certain builds running really well, and has had issues with others:

    https://c3junkie.com/?page_id=280

    The 9mm version is often called the “amphibian” build. He does a lot of experimentation, but basically recommends:

    CMMG BCG and barrel kit
    VLTOR A5 length buffer tube extension
    Kynshot RB5007 hydraulic buffer
    Tubb 5.56 flatwire spring
    RDB Endomags

    He’s got .40 s&w and .45acp versions up on his website now.


    Agreed on the mags. I guess I was referring to the RDB ones, I didn’t realize they made a different version for non RDB.


    Sent from my iPhone using Tapatalk
     

    woodline

    Active Member
    MDS Supporter
    Jan 8, 2017
    1,888
    Agreed on the mags. I guess I was referring to the RDB ones, I didn’t realize they made a different version for non RDB.


    Sent from my iPhone using Tapatalk
    That is what I took your post to mean. I was agreeing with you, but was being specific in my post. The non RDB mags don’t have nearly as good a reputation as the RDB ones, though some have used them heavily with no issue on direct blowback 9mms.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    16,207
    PA


    Some people run them at competitions. Have played around and shot the MBX, taccom(adjustable and magnet delay), the Kynshot hydraulic setups, RDB, and short stroke/heavy buffer. Most everyone is interested in the best buffer system without having to spend the money on the new roller delayed JPs or an MPX to get the lightest recoil.

    The problem with most is that you really can't fight physics, and all but the RDB work opposite of what is really needed for blowback operation. The MBX, kynshot and taccom adjustable have a 2nd or 3rd stage cushion on the buffer, so it doesn't have as much slap when bottoming in the tube. THe MBX uses air pressure in the tube to cushion, and most use heavy springs for the same idea, to slow the fast moving BCG/buffer. Problem is they all give up some weight for the spring/cushion design, and the lighter mass provides less resistance during the short powered "blowback" portion of cycling, when the pressure in the barrel drops enough so the brass can slip from the chamber, powered by the burning powder, to push the BCG rearward. This only happens over the 1st 1/4" or so of bolt travel, the rest of the time, inertia and spring pressure is all that is controlling bolt speed.

    Delayed blowback uses rollers or the angled lugs to provide a mechanical disadvantage for this first bit of movement, where rollers act on a wedge to push the buffer against the recoil spring around 3x the distance as the bolt face is moving, basically creating more resistance, giving proper bolt speed, and less spring pressure or bolt mass needed. With straight blowback, really only bolt/buffer mass slows the blowback, but also increases bolt inertia, shortening the travel helps reduce some of the slap and dot movement. The lighter cushioned buffers tend to have more recoil, but less "slap", and can have issues with ammo outside of a relatively narrow power factor. THe Taccom magnetic delay is cool, but IMO it doesn't work, it makes the charging handle hard to pull, but I think like spring force, the magnetic force really doesn't do much to slow that first bit of movement compared to raw mass. Kynshot does have a heavy short stroke buffer that has good mass from add-on weights, some cushion from the hydraulic, and is kinds the best of both adding mass and cushion. My KVP 10oz had 4 floating tungsten weights and weighs 10.5oz, so nice slow blowback, good deadblow effect to soften recoil and chambering, and some cushion as the weights have rubber pads between them. For competition I use silicone plugs for the "short stroke spacer" instead of hard plastic spacers. There is more cushion, and feels about the same as the far more expensive kynshot, but is cheaper, more reliable, and the plugs are easily replaceable if they wear.
     

    rbird7282

    Active Member
    Dec 6, 2012
    13,904
    That is what I took your post to mean. I was agreeing with you, but was being specific in my post. The non RDB mags don’t have nearly as good a reputation as the RDB ones, though some have used them heavily with no issue on direct blowback 9mms.

    :thumbsup::thumbsup:
     

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