Bullet weight for SBR

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  • Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    I was not expecting better accuracy out of my SBR than my 16" dissipator but @ 25 yards, it was pretty poor (2-3"groups from bags) using my 55gr plinker loads. I had been using these 55gr reloads that my dissipator pretty much touches holes at 50 yards.
    I have a Bushnell red dot on it.
    Today, I used some 69gr SMK reloads and it was much better.
    Is this typical of an SBR to like heavier bullets?
     

    HordesOfKailas

    Still learning
    Feb 7, 2016
    2,205
    Utah
    My understanding was that a lighter bullet was easier to stabilize than a heavy one. All things being equal, an SBR has a shortened barrel meaning the bullet spends less time inside being stabilized. Physically, I'd have expected the opposite. Just thinking out loud.
     

    mopar92

    Official MDS Court Jester
    May 5, 2011
    9,513
    Taneytown
    I was not expecting better accuracy out of my SBR than my 16" dissipator but @ 25 yards, it was pretty poor (2-3"groups from bags) using my 55gr plinker loads. I had been using these 55gr reloads that my dissipator pretty much touches holes at 50 yards.
    I have a Bushnell red dot on it.
    Today, I used some 69gr SMK reloads and it was much better.
    Is this typical of an SBR to like heavier bullets?

    How where you shooting? Absent outside influences, an SBR will be mechanically more difficult to shoot accurately, shorter sight radius, harsher recoil, and lighter meaning it takes a smidge longer to settle down. You said bags, front and rear? Sitting at a bench? Are the grips different?
     

    Minuteman

    Member
    BANNED!!!
    :thumbsup:
    1:12 favours lighter bullets; 1:7 favours heavier bullets.

    Yes, almost always true.

    But:

    FIFY, a common misconception because the longer bullets are heavier.
    But weight has very little to do with it.

    Unless there is some dramatic aerodynamic at work (weird bullet shape), but actually the length of the bullet, not the weight that matters the most.


    If you go with 300BLK in an SBR (or pistol) when you get around 9" barrel length, 300BLK is already optimized. generally
     
    Last edited:

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    68-69gn seems to be the cut off for light(short) vs. heavy(long) from my experiences. All my guns(most have 1:9 ROT) shoot them fine. I have limited experience shooting anything heavier than 55gn out of my 10.5'' SBR. Sounds like something I need to look at in the near future.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Red Dot.
    When looking at accuracy, I rest front and rear on bags. Sitting at a bench.
    Geisselle SSA-E trigger

    10.5" Barrel. 1:7 twist Chrome Moly
     

    mopar92

    Official MDS Court Jester
    May 5, 2011
    9,513
    Taneytown
    Red Dot.
    When looking at accuracy, I rest front and rear on bags. Sitting at a bench.
    Geisselle SSA-E trigger

    10.5" Barrel. 1:7 twist Chrome Moly

    Should perform decent with 55 grainers. What type of bullet? Varmint, FMJ, etc? I know the Swiss ammo 55 grain uses a thicker jacket to help stabilize better. Some OLD stuff used a very thin jacket that could destabilize in the barrel and shred the jacket and some very thin varmint stuff could theoretically do the same.

    One thing I do when shooting ARs for accuracy is flip my firing hand thumb to the firing side of the grip. (Helps isolate the trigger muscles)
    Free float or standard handguard?
    Who made the barrel?
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    55 fmj from Xtreme reloads with 25gr H355 I have some reloads with better nosler bullets I will try next It's not my shooting technique because I'm shooting the same with my dissipater upper on the same lower

    Upper is from Joebobs
    Radical Firearms
     

    mopar92

    Official MDS Court Jester
    May 5, 2011
    9,513
    Taneytown
    55 fmj from Xtreme reloads with 25gr H355 I have some reloads with better nosler bullets I will try next It's not my shooting technique because I'm shooting the same with my dissipater upper on the same lower

    Upper is from Joebobs
    Radical Firearms

    Radical firearms hasn't been putting great barrels out to be honest. I've handled and shot 5 or 6 of em, and none of em I could get to go below 3" with good ammo. You may have to just work up an SBR load and a 16" load for your ARs for accuracy. Try a few different bullets and weights and see if you can find one it likes.
     

    SCARCQB

    Get Opp my rawn, Plick!
    Jun 25, 2008
    13,614
    Undisclosed location
    I like 1:9 for 5.56/.223 barrel 10.5 or shorter.

    For these abbreviated tubes, you lose a lot in terms of velocity. So i use 55 grains or lighter projectiles to compensate. Lighter varmint loads work well and stabilize in 1:9( =40-55 grain)
    The 5.56 works well if you can keep it fast. Thats why i use the lighter bullets in SBRs.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    I ran some factory 55gr ammo that had more velocity than my 55gr reloads. It grouped about the same @ 50 yards. the 69gr reloads were about 1.5" @ 50 yards with the red dot.
     

    Sticky

    Beware of Dog
    MDS Supporter
    Mar 16, 2013
    4,501
    AA Co
    55 fmj from Xtreme reloads with 25gr H355 I have some reloads with better nosler bullets I will try next It's not my shooting technique because I'm shooting the same with my dissipater upper on the same lower

    Upper is from Joebobs
    Radical Firearms
    What optic/sight on the Dissy? Could it be a difference in sights/optics? Red dots are not as accurate as a scope, especially the less costly ones in my experience.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    What optic/sight on the Dissy? Could it be a difference in sights/optics? Red dots are not as accurate as a scope, especially the less costly ones in my experience.

    Bushnell TRS-25.

    I have not tried putting the TRS 25 on my other AR to compare though.
    The other AR (16" dissipator) has regular peeps but nice long sight radius.
     

    Sticky

    Beware of Dog
    MDS Supporter
    Mar 16, 2013
    4,501
    AA Co
    I was thinking swap em, but if they are both red dots or open sights, it probably won't matter much. The longer sight radius does help a lot, no question.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Bringing this back up cause I'm done with this barrel, I want to put in something else. I like to shoot steel @ 100 yards and I don't like to spend more $ per bullet to hit the target. I had the SBR out twice in the last 2 weeks and its getting about 3-4MOA with factory Remington (the worse) or my reloads (better). This is with a 3X P223 Nikon Scope on it and 55gr. I also ran my Delton with a red dot and it was 2 MOA even with me shooting with the red dot that upper is 1MOA with reloads and a scope.

    I pulled the barrel off this morning before work Just to make sure nothing was stuck, or hard for me to get off before ordering another barrel. So, all is good.

    What is a bang for the buck 1:9 10.5" barrel?
     

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