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Suggestions for SBR barrlel length and why?

Fred @ Bison Tactical

Fred @ Bison Tactical

Bison Tactical
Commercial Supporter
Full Member
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    • May 18, 2012
    1,818
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    Boulder, CO
    www.bisontactical.com
    #1
    I am relatively new to SBR's, and would like suggestions...

    I am looking to build a SBR on a small frame AR15 platform. I would like mobility, but with good accuracy out to 300 yards.

    I would like to stick with 5.56, and would be happy to hear suggestions on upper manufacturers as well as what barrel length people think is a good choice for an SBR to balance mobility with reliable function and accuracy.

    I also plan to shoot suppressed 5"-7" suppressor.
     
    #2
    In a DI gun I would recommend an 11.5" setup from BCM. Here's a good snippet of info from as to "Why" 11.5 instead of 10.3/.5. (mk18)

    A: Dwell time.
    Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

    The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

    I don't own any BCM rigs but I have shot several. They certainly are smoother than 10.5" rifles.

    In a piston rifle I would highly recommend the LMT 12" MRP piston. Monolothic upper, will run much cleaner with your can, adj gas block, and just simply built like an absolute tank. If you don't like the piston setup you can sell your BCG & barrel and get a DI setup to use in the same chassis!
     
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    #3
    hypno02 said:
    In a DI gun I would recommend an 11.5" setup from BCM. Here's a good snippet of info from as to "Why" 11.5 instead of 10.3/.5. (mk18)

    A: Dwell time.
    Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

    The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

    I don't own any BCM rigs but I have shot several. They certainly are smoother than 10.5" rifles.

    In a piston rifle I would highly recommend the LMT 12" MRP piston. Monolothic upper, will run much cleaner with your can, adj gas block, and just simply built like an absolute tank. If you don't like the piston setup you can sell your BCG & barrel and get a DI setup to use in the same chassis!
    Click to expand...

    BCM = Bravo Company ?
    Also, is there significantly more carbon impact on the suppressor in a shorter AR platform ?
     
    #4
    I have both the 10.5" and a 11.5" that I swap back and forth on a SBR lower. The 11.5" gets run 95% of the time due to the dwell time issues, accuracy, and comfort. That one inch makes a noticeable difference. I should have gone with a piston set up as suppressed you get a snoot full of gas. I have noticed quite a bit of carbon when run suppressed in the 10.5" and 11.5", but I just keep it well oiled. I can't compare it to a DI style 16" as my full size carbine is a piston operated. SBR and suppressed I would recommend an adjustable gas block to further tune the recoil/dwell time.
     
    #5
    I have zero dwell time, accuracy or comfort issues on any of my 3 10.5" sbrs in 5.56 and 300blk. I run adjustable gas blocks and spikes heavy buffer and they run like a swiss watch. I have many friends that have 10.5" and they haven't had any issues either. This is news to me.
     
    #6
    11.5", 12.5", 14.5" are common answers for 556 with good reliability. 10.5" you start losing muzzle velocity quickly which will affect bullet stability out to distance (but maybe be good to 300yds? I dunno). If you want less than 11.5" 300 blk is a better bet.
    Or do what the new hotness is and SBR a 6.5 Grendel. (I've gone this route).
     
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    #7
    11.5 but a Sionics Reduced Gas Port (RGP) barrel. If you go with just about any other barrel manufacture get a SLR adjustable gas black.

    11.5
    Adjustable gas block
    Vltor A5H2
    LMT E carrier
    Giessele charging handle
    Suppressor brake of your choice. I prefer dead air.
    Supressor
    Enjoy very soft shooting SBR
     
    #8
    11.5” is a good all around length. I have a bunch of 10.3-10.5” SBRs and some in the 12” range. No issues with any of them. I settled on 11.5” in the end. Haven’t taken it beyond 200 though.
     
    #9
    I get 2100 out of my 10.5" 300blk Rainier Ultramarch with 125 TMK and H110. Stupid accurate and makes consistent hits on steel out to 500.

    My 10.5" DD 5.56 with a T1 with 55 VMAX is 2560 and with the Red Dot hits on still is easy to 200. Big drop after that
     
    #12
    As folks mention above, the 11.5" is the consensus go to. I have a couple of 10.3" and 10.5" guns and have had zero issues with accuracy or function. I always end up taking out my LMT 12" piston. Runs great. I can ding steel out to 500 yards. Handles a suppressor like a champ. Can't say enough good things about the LMT with their 12" piston kit.
     
    #13
    I like and use 11.5. Accuracy is never an issue. Adj gas block is very nice with suppressor. I would not shoot one without except in a dire emergency.
    Not sure on your use but do not expect good kills even at close range on larger game. It will kill but not like the 18' barrels. 77 grain bullet is still the answer.
     
    #15
    I went with 11.5" for a duty rifle. Everything I've researched says below 11.5" you start to run into other issues like was mentioned with dwell time etc. Mine is suppressed 99% of the time so I opted to do everything I can to slow the cycle rate down with weight as opposed to an adjustable gas block. I have a Vltor A5 system with their heaviest buffer weight in it and an LMT Enhanced bolt carrier which is supposed to be designed for suppressor use. I do NOT use their bolt however as I had tons of issues with his failing to extract. The gun gets filthy, but I've got 1100 rounds through it without cleaning so far and no malfunctions. I just lube it a little before a range session and keep shooting. 12.5" wouldn't be a bad length either and there are some reputable guys out there saying 12.5 is the way to go with a mini can.
     
    #18
    Piston AR’s are usually a NO-Go. Stick with DI.

    That’s why I mention SLR gas block, LMT E carrier, Giessele or similar charging handle with the gas buster shelf.

    Those three things will knock down a lot of your gas blow back and get it out of the gun instead of in your face.

    Getting suppressor gas in your face makes you cry like a little bitch. Lol
     
    #19
    Kadams1563 said:
    Piston AR’s are usually a NO-Go. Stick with DI.

    That’s why I mention SLR gas block, LMT E carrier, Giessele or similar charging handle with the gas buster shelf.

    Those three things will knock down a lot of your gas blow back and get it out of the gun instead of in your face.

    Getting suppressor gas in your face makes you cry like a little bitch. Lol
    Click to expand...
    LOL every time I shoot my work SBR (11.5 BCM) with a Surefire Mini 2 I leave the range like I just cried. Blow back is retarded.
     
    #20
    10.5 or 11.5. Can't say if one is really THAT much better than the other. I went 10.5" and had no problem on calm days hitting steel out to 500-600yd with 75gr HPBT loads (2300fps). Accuracy was 1.5-2MOA with a $75 no-name barrel.

    Stability/accuracy was not affected with a 1:7 twist. Not that I could tell, anyway. An adjustable gas block is a necessity with SBR IMO, even more so if you're going to suppress it. I had my adjustable gas almost all the way closed to get 3-4 o'clock ejection.
     
    #22
    12.5" 5.56 and 6.8 here, both ARP barrels w/ mid gas and very accurate. Gas face isn't bad with either one using a can, the PRI handles never worked for me.
     
    #23
    What is the shortest barrel length recommended by the manufacturer of the suppressor(s) you plan on using? Go with that length.
     
    #25
    I've got a couple thousand rounds through a 7.5" Noveske diplomat barrel with zero issues. It eats everything. It's wearing a collapsalbe stock to maximize the footprint. I agree, in general, that the 10.5 to 11.5 uppers run well but chosen equipment matters...a lot. Those who turn the page and then start conversations about barrel length and terminal ballistics need to look in the mirror and go back to their 16" barreled rifles. Stand down range at 300m and tell me how that 75gn pill out of the SBR feels. Purchase what you will shoot and use. You can always get another upper!
     
    #26
    hypno02 said:
    Yeah that is just terrible advice.

    OP Mentioned to balance mobility with reliable function & accuracy. Anything less than 10.5 is not going to give him that.
    Click to expand...

    What is the shortest barrel length recommended by the manufacturer of the suppressor(s) you plan on using? Go with that length (upon hypno02's approval).

    There, fixed it.
     
    #27
    Have you thought about 300blk instead? Unless you build a sbr 5.56 specifically to be suppressed with adjustable gas block etc, your going to get some serious in your face blow back. I wish I could remember the minimum length of a suppressed 556. I wanna say 11.5” but not positive. Then add a muzzle brake and your at
    13-14”. Kinda defeats the purpose of an SBR imo.
    300 blk in 9” for best ballistics and be done with it.
     
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    #28
    Poor bastard can’t make a decisions based on THIS thread.

    Everything about longer barrels is better except the size. So get a longer barrel and a shorter can. I like 11.5 with a 5” can because I couldn’t get a KAC 12.5.

    Smaller gas ports are better. You just need it to run in the cold with your ammo. You don’t need it to run with Wolf or to run hard. A smaller ported DI barrel will run cleaner than an HK416 with a can because it unlocks later, and the carbon is mostly coming back through the barrel not through the gas tube!

    300BLK is a viable option especially at 10.5” and less, but it depends on your logistics. Are you a pig hunter sport shooter or LEO? Do you travel or stick close to home? Does someone issue you ammo or let you load from their can? There is a reason some government users have 13” 308s and 7.5” 5.56s and civilian users mostly don’t/shouldn’t.

    An adjustable gas block is a fix for an overly generous gas port. That’s all. Drill it right the first time and you don’t need that complexity.

    Longer barrel shorter can! It’s an autoloading SBR it will never be quiet enough to shoot regularly without hearing protection. Don’t chase decibels.

    If I was getting a piston gun I would get the PWS. Long stroke is better. I have two KAC rifles now instead.

    Use more buffer.

    Use expanding bullets over fragmenting in an SBR.
     
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    #31
    BravoSector1 said:
    Plus muzzle brake or flash hider. Might as well save your $200 and 9 month wait. Not discounting the capability of said kit but an SBR...is an SBR. Might as well run a 14.5 and pin/weld the flash hider at that length!!!
    Click to expand...

    I run a 10.5” SBR suppressed with a Crux Ark 30 can and an adjustable GB. She runs really well and have run her hard in a 2 day class without any malfunctions. I have also had her out to 300 yards during the class on silhouette plates with a T2 and Wolf Gold ammo and made consistent hits.
     
    #32
    BravoSector1 said:
    Plus muzzle brake or flash hider. Might as well save your $200 and 9 month wait. Not discounting the capability of said kit but an SBR...is an SBR. Might as well run a 14.5 and pin/weld the flash hider at that length!!!
    Click to expand...
    It really depends on the purpose. My SBR is built around having a suppressed rifle the same length as a 16" gun. An 11.5" barrel with average length 5.56 suppressor(I bought the SiCo Saker 556) OR a 12.5" with a mini version will accomplish that.
     
    #33
    Completely agree with the posts. OP, just need to zero in on what this tool is for. The gerber tool SBR, 10.5-12", along with a can will get you into a rifle with an OAL about equal to a standard 16" rifle. If size, transport and or concealment are more important than suppression you can go well below 10.5. Again, you can always get another upper!
    30761799527_fc5383e8e1_b.jpg

    45651770382_50e5b0071c_b.jpg
     
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    #37
    I'm going for LESS dwell time, LIGHTER buffers, SMALLER gas ports (usually via an adjustable gas block), and full mass bolt carriers in my personal AR's used ONLY suppressed.

    Noveske 10.5" 5.56 with carbine gas system & Vltor A5-H1 buffer plus Surefire FA556-212 suppressor
    Noveske 12.5" 5.56 with mid-length gas system & Vltor A5-H1 buffer plus Surefire SOCOM RC-2 suppressor
    Bartlein 12.5" 6.5 Grendel with carbine +1" gas system & Vltor A5-H1 buffer plus Thunder Beast Ultra 7 6.5mm suppressor
    Proof CFW 16" 5.56 with intermediate gas system & Vltor A5-H1 buffer plus Thunder Beast Ultra 7 .223 suppressor
    Proof CFW 18" 5.56 with rifle gas system & Vltor A5-H1 buffer plus Thunder Beast Ultra 7 .223 suppressor
    Bartlein 20" .224 V with rifle +2" gas system & Vltor A5-H1 buffer plus Thunder Beast Ultra 7 .223 suppressor

    Almost zero felt recoil. Superb accuracy. The downside is they need to be reasonably well lubed and the 5.56's need to be fed only full power ammo.
     
    Last edited:
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    #38
    If you can afford the ammo and like short barrels: 300 AAC Blackout is my recommendation . 30 cal. AK-like ballistics in supersonic and whisper quiet subsonic suppressed.
    An 8" & 9" 300 BO became my solutions. I started with a 9" AAC upper (with non-adjustable GB). It runs GREAT with both supersonic (with or without suppressor) and subsonic (with suppressor) loads.

    Then I built a 300 BO to use as a non-ATF "trunk-gun" with the same characteristics (but without a stock). So, I took an LMT upper, Wilson Combat 8" barrel (also with non-adjustable GB), some really good mil-spec parts and attached a Shockwave brace on a new stripped lower. Now I can legally cross state lines with my "Pistol" and don't need to file any ATF paperwork. It runs GREAT as above.

    I prefer not to use an adjustable GBs because they have been known to create their own cleaning/sticking issues. K.I.S.S. is my moto. Both 300s run great both supersonic (with or without a can), and subsonic (only with a can), using heavier buffer and spring combo. Nothing to tune, adjust or clog.

    BTW, I don't see any real purpose running subsonic without a can. Shooting supersonic loads through the suppressor does cause more gas blowback however, but that’s a trade off I’m willing to deal with to K.I.S. So, I don’t often use the suppressor when the use of supersonic loads is indicated. But if silent running is the goal, subsonic rounds through a can work very nicely. Different situations call for different solutions and the short 300 BO can fill widely different roles.
     
    Last edited:
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