Optimum SBR barrel length

Discussion in 'AR-15 Discussion' started by griz59, Jul 27, 2015.

  1. griz59

    griz59 New Member

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    Taking all things into account (ballistics, performance suppressed, ergonomics, etc.) what would be the "best length" for a short barreled rifle? I know "best" is a touchy term and personal preference has a lot to do with it but I have no experience whatsoever with SBR's. And on that note, with a majority of shots under 200 yards and the intent of running suppressed would you go 5.56 or 300blk?
     
  2. Sniper03

    Sniper03 Supporting Member Supporter

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    Griz,

    I personally would not go shorter that a 10" Barrel. And especially taking in to consideration possible 200 yard shots. As far as suppressed the 300BLK is phenomenally quiet when shooting subsonic 300BKS out of it! You can literally hear the Bolt slap shut on the rifle! As far as the 5.56 if you buy a suppressor for it buy a 30 Cal Suppressor. *They are quieter on the 5.56 rifle than the 5.56 Suppressor.
    And you can use it on a 30 Cal like the 300 BLK or 308 later if you want too!
    03
     

  3. fsted2a

    fsted2a Active Member

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    I personally wouldn't go shorter than carbine length. If you do, get an adjustable gas block so you can tune your gas system. Pistol length gas systems can be over gassed, causing jamming and other malfunctions. Suppressors tend to increase back pressure the same as mufflers which also must be considered.
     
  4. Alpha1Victor

    Alpha1Victor New Member

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    I have a 10.3 that I love. It's 5.56 and runs like a top. I love 300 blackout but I only keep guns that I can find ammo for in a shtf situation.
     
  5. tlay

    tlay New Member

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    I have a 10" barrel on a 300blk pistol. I reload so I can taylor what works well on my gun. If you are going to limit your shooting to 200 yds. why not a 300 blk ? It will give you a larger bullet and if you want quiet you can add a can.
    I reload using a 168gr hpbt and it shoots great at 200yds. There is some drop but I sight in at 75yds for pigs.
     
  6. primer1

    primer1 Well-Known Member Supporter

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    Optimum length is dependent on what caliber. If you are sticking with 5.56, then a SBR isn't what you need. The 5.56 uses all its powder at around 18 inches, depending on load.

    If you are looking to blast the cap off your head, stick with the short barrel 5.56 and leave the can off.

    As far as the .300, I don't know enough about it to fully comment, but the optimum length will be much shorter with the subsonic loads vs. the 2000+ fps stuff.
     
  7. 70cuda383

    70cuda383 New Member

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    question on the optimum length... I don't know a lot about reloading/hand loading, but heard there are pistol powders and rifle powders? pistol burns much faster to get pressures up in the shorter barrels, but burns too fast and will blow up your rifle?

    If that's true, is it at all possible to mix pistol and rifle powders to get an optimum charge in a 16" or shorter barrel?
     
  8. primer1

    primer1 Well-Known Member Supporter

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    I currently don't reload either, but I definitely wouldn't mix powders! The burn rate would be too unpredictable. With the wide variety if powders on the market these days, there is no need to mix.
     
  9. sweeper22

    sweeper22 New Member

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    At close-short-medium range, 300blk is a way better option for a suppressed SBR in my experience. Larger diameter plus 3X the bullet weight...and generally as quiet or quieter than a similar 5.56. If they're gonna sound about the same, have equal capacity, and run at identical velocities; why not have a triple-weighted 30-cal bullet? That's way more energy delivered with little sacrifice. Plus, acheiving perfect cycling from a subsonic 300blk will prove far easier than doing so with a subsonic 5.56. But with one SBR stamp (tied to your lower) and one suppressor stamp (30-cal), you can also add a 5.56 SBR upper (or 6.8, or 7.62x39, etc) to use within the same system.


    For a 300blk, you want 8-12" and a pistol length gas system. For 5.56, I feel like anything under 10" results in diminishing returns with limited suppression potential. So for a 5.56 I'd go with a carbine gas system on a 10.5-14" barrel.

    If you want to suppress a sub-10" AR, 300blk is by far the best option.
     
  10. officerX

    officerX New Member

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    From the research I've done, 9" is the optimal length for 300blk.
     
  11. fsted2a

    fsted2a Active Member

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  12. sweeper22

    sweeper22 New Member

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    That's mostly true, but totally subjective. We're talking about a case-by-case sliding scale here. Are you using a suppressor? What bullet weights? How much powder? Gas length? Buffer weight?...etc, etc.

    8-10" is generally a good bet for a 300blk suppressed SBR. You want a pistol length gas with 180+gr bullets. Mine is 12", and runs great. But I plan to add an 8.5" upper as well.

    I see massive potential in a 300blk supr/sbr, and minimal value in a 5.56 of similar stature.
     
    Last edited: Jul 29, 2015
  13. Biohazard2

    Biohazard2 Member

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  14. fsted2a

    fsted2a Active Member

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  15. Parnelli

    Parnelli Member

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    I have a 12" and I wish I would have gone 14".The reason is if I had the 14" I could use the area from the threads on the barrel, back to the handguard as a back chamber to relieve pressure in a suppressor and give two points of attachment. With the 12" I only get about 1" of back chamber. A three inch chamber would work better when a lot of rounds go out the barrel fast.
     
    Last edited: Jul 29, 2015
  16. Balls004

    Balls004 New Member

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    I settled on a 10.5 inch pistol length gas system in 300 BLK for mine. No problems from it with either sub or super rounds.
     
  17. sigman84

    sigman84 New Member

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    I like the 8-10 inch barrels for 300blk. If I want 16 inch barrels or larger I'll go 5.56.
     
  18. TexasGunner

    TexasGunner New Member

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    [​IMG]

    8.5" barreled 300 BLK SBR. It will run subs suppressed and unsuppressed. Love this gun.

    [​IMG]

    My 9mm AR9 has a 5.5" barrel. Bang steel plates at 100 yards all day.

    [​IMG]

    I got a mag block and Colt style mags for when I want to run the 9mm as an SBR.