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Thread: 300blk rifle in a regular length barrel

  1. #1
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    300blk rifle in a regular length barrel

    I recently plunged into the 300blk pool with a factory upper for one of my sbr's. Having done the reading for years, I get that the original design philosophy and use case was for short barreled suppressed application. And I really like it.

    So now I got to thinking; how would shooting 125gr supers out of a 14.7 or 16" barrel stack up against 5.56 or 7.62AK? In terms of ballistics and terminal performance, do the supersonic rounds hang in better than the subs past 200 or 300 yards?

    I'm currently swimming in 5.56, so we're not talking replacement here. Just curious if I could make a go-to out of it. Anyone doing this or have any great insights? As far as gun buying goes, this should be like my 127th priority, but we know how that works out. You get the bug, you get the bug. Someone talk me out of trying this.

  2. #2
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    The SuperSonics in a longer barrel should equal or better the 7.62x39 especially with the better choices in bullets available.

  3. #3
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    Quote Originally Posted by nick84 View Post
    I recently plunged into the 300blk pool with a factory upper for one of my sbr's. Having done the reading for years, I get that the original design philosophy and use case was for short barreled suppressed application. And I really like it.

    So now I got to thinking; how would shooting 125gr supers out of a 14.7 or 16" barrel stack up against 5.56 or 7.62AK? In terms of ballistics and terminal performance, do the supersonic rounds hang in better than the subs past 200 or 300 yards?


    I'm currently swimming in 5.56, so we're not talking replacement here. Just curious if I could make a go-to out of it. Anyone doing this or have any great insights? As far as gun buying goes, this should be like my 127th priority, but we know how that works out. You get the bug, you get the bug. Someone talk me out of trying this.
    May be helpful


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    7.62x39 is gonna give you more energy vs supersonic .300bo, but shooting ADI MSR Sierra Matchking .300bo (125gr. super) thru my PSA 16” 300bo upper still groups better than my PSA 16” 7.62x39 upper shooting Golden Tiger steel case or surplus Yugo m67. Now if I went up to Hornady SST Black 7,62x39 it might be different, but for what that costs I might as well buy Hornady Black 6.5 Grendel.

    Going from 8” to 16” barrel is only gonna net you another 200 to 300 FPS. I first bought a 16” .300bo upper before I got in to braced pistols and added an 8” .300bo so I put a red dot on the 8” for subs and a 1-4x scope on the 16” but shooting them side by side, not much difference.

    If you’re wanting to shoot out to 300 yards, 6.5Grendel is a much better caliber.

    Having an AR in 7,62x39 is a good option, steel case ammo is cheap & plentiful, but very limited in bullet selection.

  5. #5
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    Quote Originally Posted by Mrgunsngear View Post
    May be helpful
    Excellent. Pretty much what I was looking for. Thanks for the video.

  6. #6
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    Quote Originally Posted by nick84 View Post
    So now I got to thinking; how would shooting 125gr supers out of a 14.7 or 16" barrel stack up against 5.56 or 7.62AK? In terms of ballistics and terminal performance, do the supersonic rounds hang in better than the subs past 200 or 300 yards?

    *** You get the bug, you get the bug. Someone talk me out of trying this.
    If you cherry-pick the right cartridges, 300BLK looks decent compared to 5.56 in a 16", mostly for muzzle energy and momentum (power factor). But the bullet starts slow and the BC's are not impressive for anything that will go over 2000fps, so it's a medium range cartridge, at best, and compares to the 762x39, not in a good way. If you're shooting beyond 300 yards a good 5.56 OTM/BTHP load will beat it badly.

    The potential benefits: larger and heavier bullet, if that matters (it probably doesn't); can switch between subsonic and supers in the same upper without adjusting anything; plays nicely with suppressors; may be legal for deer in a few states where .223 is not; good option if you have an existing SBR and suppressor setup and want the ability to reach out a little farther in the same caliber.

    It's really a niche option, not a jack of all trades.

  7. #7
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    Quote Originally Posted by SomeOtherGuy View Post
    If you cherry-pick the right cartridges, 300BLK looks decent compared to 5.56 in a 16", mostly for muzzle energy and momentum (power factor). But the bullet starts slow and the BC's are not impressive for anything that will go over 2000fps, so it's a medium range cartridge, at best, and compares to the 762x39, not in a good way. If you're shooting beyond 300 yards a good 5.56 OTM/BTHP load will beat it badly.

    The potential benefits: larger and heavier bullet, if that matters (it probably doesn't); can switch between subsonic and supers in the same upper without adjusting anything; plays nicely with suppressors; may be legal for deer in a few states where .223 is not; good option if you have an existing SBR and suppressor setup and want the ability to reach out a little farther in the same caliber.

    It's really a niche option, not a jack of all trades.
    Sierra .224 77 Gr Match King G1 BC .362

    In 5.56mm

    Started @ 2650 FPS (16" barrel) with a 50 yd zero

    @200 Yds -1.1" low (0.2 Mils) 833 Ft lbs of energy
    @300 Yds -10.6" low (1.0 Mils) 686 FT lbs of energy

    Barnes .308 120 Grain TAC-TX BT G1 BC .358

    In a 16" 300 Blackout

    Started @ 2200 FPS with a 30 yard Zero (to optimize drops for the slower projectile)

    @200 Yds -0.3" Low (0.0 Mils) 902 Ft lbs of energy
    @300 Yds -14.8" Low (1.4 Mils) 717 Ft lbs of energy

    I don't know what your looking at but the 300 Blackout appears to be superior to the 5.56mm at all ranges under 300 yds.

    For engagements over 300 yds you better have a good scope on the superior 5.56mm and know how to use it at range, because you going to need it.

    It seems to me that the 5.56mm is sort of a niche option, and compares to the 7.62x35mm, not in a good way. But for engagements over 300 yds it is better, but only with a properly scoped rifle.

    IMHO and YMMV.....
    Last edited by BobinNC; 08-26-20 at 21:02.

  8. #8
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    300BLK v 556 Trajectory.png

    If this has attached properly, it will give a good ballpark on Barnes 110gr velocities. From this you can calculate drops on any good ballistics program. Energy will top the 5.56 due to heavier bullets but the trajectory will be more parabolic. At longer range, you’ll have to know your come-ups.
    Last edited by SBRSarge; 08-26-20 at 23:57.

  9. #9
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    For what it's worth, I had a 16" 300 BLK that I used for deer hunting.
    The furthest I took a deer with the 300 BLK was at 150 yards. I was using Barnes 110gr. Shot placement was reasonably good. But I was not really completely satisfied with how it put down that deer at that range.
    The remainder of deer taken with this rifle were at or under 100 yards and were satisfactory in how the deer were taken.
    To me, the 300 BLK took deer like a 30-30.
    I have sold that weapon.
    This may not be useful to you, but it was my practical experience regarding 300 BLK at different ranges.

  10. #10
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    I've taken several deer w/ my 12.5" & the same 110gr hand loads & reached a little further maybe to 200 with great results...our S. Tx doe don't get near as big as other parts of the country however. This particular upper is also sub MOA & inspires confidence as well.


    Quote Originally Posted by LDM View Post
    For what it's worth, I had a 16" 300 BLK that I used for deer hunting.
    The furthest I took a deer with the 300 BLK was at 150 yards. I was using Barnes 110gr. Shot placement was reasonably good. But I was not really completely satisfied with how it put down that deer at that range.
    The remainder of deer taken with this rifle were at or under 100 yards and were satisfactory in how the deer were taken.
    To me, the 300 BLK took deer like a 30-30.
    I have sold that weapon.
    This may not be useful to you, but it was my practical experience regarding 300 BLK at different ranges.
    "You cannot invade the mainland United States. There would be a rifle behind each blade of grass."
    Japanese Admiral Yamamoto, 1941




    "A wise man's heart directs him toward the right, but a foolish man's heart directs him toward the left."
    Ecclesiastes 10:2:

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