300 BLK barrel length(super sonic)

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  • offroaD

    Active Member
    Jun 1, 2011
    566
    I plan on building a 300 blk upper for deer hunting as it's more cost effective for me than buying a new bolt gun. I know people build 300blk guns because they are very quiet when shot with a suppressor. That's really not my thing and I'm only going to use super sonic rounds since it will be my deer upper. Since I'm putting the upper together my self I figured I'd build it to harness the maximum energy potential of the 300 blk round.

    Increasing barrel length has diminishing returns, and the information I'm finding online says the 300blk round burns all of it's powder 8-9" into the barrel. I'm guessing this is for subsonic loads, or does this hold true for super sonic rounds as well? Is it worth going longer than a 16" barrel for super sonic rounds?

    Given my usage would the carbine gas length suit me better than the pistol or will the difference in dwell time not make a difference in bullet velocity? As I understand manufacturers are switching to the pistol length system so people can shoot subsonics more reliably but like I mentioned before I wont be shooting subsonics.

    I'm pretty much doing the opposite of what everyone else is doing with the 300 blk platform which is making it hard to find the correct information. All my shots will be within 150 yards which is well within the capability of the round, but knowing I set it up just right for that extra 2% difference will give me that good feeling.
     

    DaemonAssassin

    Why should we Free BSD?
    Jun 14, 2012
    23,970
    Political refugee in WV
    Go with a 16" barrel.

    They are for the most part correct that most of the powder is burned within the first 8-10" of the barrel for supers or subs.

    Don't bother with a carbine gas system, the cartridge isn't designed to operate on carbine gas. Get the barrel with a pistol length gas system, due to that is what the cartridge was designed for.

    I built a 300BLK upper for the exact same reason you did. I took my time with it and did some accuracy enhancing things, during the build that paid off in spades. You can see the 300BLK in the thread I linked to.
    https://www.mdshooters.com/showthread.php?t=213710

    I'd be willing to offer advice an input, if you would want it.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    If you're only going to shoot supers and cost is a concern, why not use 7.62x39, which is ballistically the same as .300AAC and WAY cheaper? The magazine situation is basically solved at this point, certainly for the small-cap mags you'd be using to hunt deer.
     

    smokey

    2A TEACHER
    Jan 31, 2008
    31,412
    For deer, 6.8 spc or 6.5 grendel would both be much better options(assuming you're sticking with an ar15 platform and not just jumping up to an ar10). 300blk is really best used as a way to get good ballistics out of a short barrel and/or suppressed. If you're sticking to 16" and not suppressing it, it's not really using it for what it's good at.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,816
    For deer, 6.8 spc or 6.5 grendel would both be much better options(assuming you're sticking with an ar15 platform and not just jumping up to an ar10). 300blk is really best used as a way to get good ballistics out of a short barrel and/or suppressed. If you're sticking to 16" and not suppressing it, it's not really using it for what it's good at.

    Agreed.
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,733
    Socialist State of Maryland
    Unless your 7.62x39 has a .308 barrel, there are more bullet choices for the .300 BO, assuming you reload. I agree with the 16 inch barrel and, since I have never seen any problems using supers in a carbine gassed upper, I would say it is also good to go.

    IMHO, the 6.8 SPC doesn't have the drive it once had. Again, if you reload, the 6.5 Grendel will give you more versatility when it comes to hunting game.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,816
    Unless your 7.62x39 has a .308 barrel, there are more bullet choices for the .300 BO, assuming you reload. I agree with the 16 inch barrel and, since I have never seen any problems using supers in a carbine gassed upper, I would say it is also good to go.

    IMHO, the 6.8 SPC doesn't have the drive it once had. Again, if you reload, the 6.5 Grendel will give you more versatility when it comes to hunting game.

    He doesn't reload. AFAIK
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    It's a versatile cartridge, runs well in ARs, and plenty have built hunting rigs around it. While it was built to be efficient in short barrels, loads vary, and there is still enough pressure to accelerate a bullet past the point it is all ignited. Most charts I have seen show around 100FPS increase per inch out to around 8 or 9, then only about 50 gained for the next few inches, and as little as 10-25FPS gained as the barrel length goes beyond 12" or so. Might not be much, but they do increase velocity, and longer barrels will reduce muzzle blast and noise even without a suppessor, and of course no need for an NFA stamp or brace. The round doesn't have the pressure curve of 5.56 or most other rifle calibers, it's more like a magnum pistol, small case capacity, and faster burning powders. The short gas system helps ensure enough port pressure and dwell, even with longer barrels, you rarely need to choke down pressure as dramatically with an AGB, or increase buffer weight as often as with 5.56. Pistol gas works with all bullet weights, and even on longer barrels with supers it isn't overgassed to the degree 5.56 often is, while carbine gas can cause problems with subs, there really isn't a benefit in recoil, velocity, or reliability to justify it.
     

    DaemonAssassin

    Why should we Free BSD?
    Jun 14, 2012
    23,970
    Political refugee in WV
    Unless your 7.62x39 has a .308 barrel, there are more bullet choices for the .300 BO, assuming you reload. I agree with the 16 inch barrel and, since I have never seen any problems using supers in a carbine gassed upper, I would say it is also good to go.

    IMHO, the 6.8 SPC doesn't have the drive it once had. Again, if you reload, the 6.5 Grendel will give you more versatility when it comes to hunting game.

    I can find factory ammo that ranges from 110gr all the way to 220gr. Reloading allows you to utilize projectiles like the 165 SGK, 168 SMK, 175 SMK, 230 SMK, and 240 SMK. Even so, the most widely found loads for range use are 147gr or 150gr. You can find 120gr OTM at WalMart in the ammo section, too.
     

    DaemonAssassin

    Why should we Free BSD?
    Jun 14, 2012
    23,970
    Political refugee in WV
    It's a versatile cartridge, runs well in ARs, and plenty have built hunting rigs around it. While it was built to be efficient in short barrels, loads vary, and there is still enough pressure to accelerate a bullet past the point it is all ignited. Most charts I have seen show around 100FPS increase per inch out to around 8 or 9, then only about 50 gained for the next few inches, and as little as 10-25FPS gained as the barrel length goes beyond 12" or so. Might not be much, but they do increase velocity, and longer barrels will reduce muzzle blast and noise even without a suppessor, and of course no need for an NFA stamp or brace. The round doesn't have the pressure curve of 5.56 or most other rifle calibers, it's more like a magnum pistol, small case capacity, and faster burning powders. The short gas system helps ensure enough port pressure and dwell, even with longer barrels, you rarely need to choke down pressure as dramatically with an AGB, or increase buffer weight as often as with 5.56. Pistol gas works with all bullet weights, and even on longer barrels with supers it isn't overgassed to the degree 5.56 often is, while carbine gas can cause problems with subs, there really isn't a benefit in recoil, velocity, or reliability to justify it.

    I'll add something to this that is slightly minor, compared to what you posted. I am able to run supers or subs out of my 16" barrels 300BLK, using a standard carbine spring and a Spike's T1 buffer (3.0 oz.), with no reliability issues.
     

    geda

    Active Member
    Dec 24, 2017
    550
    cowcounty
    I just came in from the woods hunting with my suppressed 300blk bolt action ruger american. This is my second year with this rifle and I have harvested about 10 deer ranging from fawns to a large 10pt with this setup. I bought this gun because it was cheap, threaded and available quick when I needed a host for my new suppressor. I am using supersonic commercially loaded hornady 125gr sst rounds loaded about 2100fps tested with a chrono. Sounds like a 22lr through a silencerco hybrid.

    While I have had great success with this round so far, I would definitely say it is a marginal deer round. I only take archery style broadside double lung shots, and do not reliably achieve pass through on larger deer. That is fine for my style of hunting, but if you are planing on hitting the shoulder or neck I would go for something with a little more power. I have very little confidence that you could double lung after passing through the thick part of the shoulder blade. I have also only had 1 out of 10 deer do the hydrostatic shock "dead right there" and it was small fawn. A 308 would be more like 5/10 for the same shot.

    I have purchased a 458 socom upper, a 45-70 encore barrel, and want to get a 450 bushmaster to play with for next season. However if you are not planning on suppressing I dont think there is an advantage to these thumper rounds.
     

    smokey

    2A TEACHER
    Jan 31, 2008
    31,412
    I just came in from the woods hunting with my suppressed 300blk bolt action ruger american. This is my second year with this rifle and I have harvested about 10 deer ranging from fawns to a large 10pt with this setup. I bought this gun because it was cheap, threaded and available quick when I needed a host for my new suppressor. I am using supersonic commercially loaded hornady 125gr sst rounds loaded about 2100fps tested with a chrono. Sounds like a 22lr through a silencerco hybrid.

    While I have had great success with this round so far, I would definitely say it is a marginal deer round. I only take archery style broadside double lung shots, and do not reliably achieve pass through on larger deer. That is fine for my style of hunting, but if you are planing on hitting the shoulder or neck I would go for something with a little more power. I have very little confidence that you could double lung after passing through the thick part of the shoulder blade. I have also only had 1 out of 10 deer do the hydrostatic shock "dead right there" and it was small fawn. A 308 would be more like 5/10 for the same shot.

    I have purchased a 458 socom upper, a 45-70 encore barrel, and want to get a 450 bushmaster to play with for next season. However if you are not planning on suppressing I dont think there is an advantage to these thumper rounds.

    Give the barnes load a try for better penetration
     

    Speed3

    Ultimate Member
    Aug 19, 2011
    7,816
    MD
    Give the barnes load a try for better penetration


    I use the 110gr barnes and they do open up well. The problem is they dont' have the knock down power, the bullet didn't exit on a 120lb doe at 75 yards.


    You wont have a problem mortally wounding a deer, but they don't drop where you shoot them either.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,816
    Just got two boxes of Lehigh 194 gr Maximum Expansion 300 Blk sub bullets today. Can't wait to load some up for next season.
     

    geda

    Active Member
    Dec 24, 2017
    550
    cowcounty
    I use the 110gr barnes and they do open up well. The problem is they dont' have the knock down power, the bullet didn't exit on a 120lb doe at 75 yards.


    You wont have a problem mortally wounding a deer, but they don't drop where you shoot them either.

    Same with the hornady 125sst, they open up real good and make lung soup but dont have enough energy left to reliably exit. Shooting down into a valley with a suppressor they really dont know what just happened, so they trot 10-20m and fall over. With an unsuppressed shot they could prob do a good 20 second sprint and cover over 100m. Not exactly what I want during rifle season.
     

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