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300 Blackout Problem

Discussion in 'Rifle Country' started by Chevelle SS, Nov 10, 2012.

  1. Chevelle SS

    Chevelle SS Well-Known Member

    My dad recently bought a 300 Blackout upper for his Bushmaster carbine and his is having a problem with it. When he shoots 115 grain it functions and operates fine, but when he fires 220 grain the bolt will not pick up the next cartridge from the magazine. :confused: Any ideas as to what the problem may be?

    NOLAEMT Well-Known Member

    sounds like the bolt is not coming all the way back. probably undergassed. Will it lock back on an empty magazine with the subsonic ammo?
  3. greyling22

    greyling22 Well-Known Member

    shounds like it's short stroking. I'm going to shamelessly copy this from stickman over here http://www.300blktalk.com/forum/viewtopic.php?f=136&t=79229

    "The 300BLK barrels are using a gas port and gas system which is designed to allow supersonic ammo to be fired reliably without a can, and for subsonic ammunition to be fired reliably with a can. Use of supersonic ammo with a can results in a functional weapon from my testing, though slightly overgassed, but subsonic ammo is going to be too weak to reliably fired without the can.

    The barrels are designed this way so there is no need for a mechanical switch on the gas block."
  4. highlander 5

    highlander 5 Well-Known Member

    Have you tried a different mag? Could be the recoil spring or the buffer may be too heavy.
    I have an upper from Noveske and went the other route,put in a Wolff XP recoil spring and a heavier buffer so I can find all my brass. I've used both the 125 and 220 gr factory ammo without a glitch.
  5. Chevelle SS

    Chevelle SS Well-Known Member

    At the risk of sounding like a ninny, is the 115 grain or the 220 subsonic? :eek:
    I tried 3 different mags
  6. Walkalong

    Walkalong Moderator

    220 is subsonic.

    If you have room in your data for more powder, it may help. You need more gas.

    I have not tried any 220 Gr stuff in my BLK yet. I have no can either.

    If your buffer is heavier than a standard one, try a standard buffer.
  7. cfullgraf

    cfullgraf Well-Known Member

    My 16" 300 BLK upper will not cycle with 220 subsonic factory ammunition and I do not have a can.

    I can get it to cycle if I up the powder charge a bit with hand loads.
    Last edited: Nov 10, 2012
  8. 68wj

    68wj Well-Known Member

    I am seeing that in a lot of places. As much as the cartridge was touted to fire in all 4 modes without the need for an adjustable gas block, it doesn't appear to be ideal on one end of the spectrum or the other.

    You can expand your gas port to work with subs better, but will be overgassed on supers. An adjustable gas block or changing the reciprocating mass can help. As is, can you run a lighter buffer or even a lighter carrier?
  9. cfullgraf

    cfullgraf Well-Known Member

    I am happy with supersonic ammunition for my plans for the rifle. I got the heavy bullet ammunition to try and heavy bullets to play with.

    The accuracy of my rifle, while not bad, is not what I would have hoped for. It is, at best, nominally 1.5" or so five shot groups at 100 yards. I have been playing with lots of different projectiles looking for the magic combination.

    The heavy bullets were just part of that experimentation.

    I am sure others have different "wants" or "desires" for there 300 BLK rifle and that is fine.
  10. oldpapps

    oldpapps Well-Known Member

    Mr. SS,

    I am far from being the most knowledgeable on the internal operations of the 300 AAC Blackout in an AR/M4, but;

    The lightest bullets I have loaded are 110gr V-Max and the heaviest were 220gr SPs. this is quite a weight range for any weapon, but to cycle an auto-loader....

    My understanding is that the lighter bullets 'over gas' and the heavy bullets are on the light side in gas. As the heavies are normally for sub-sonic and use with a 'can', the uses of the 'can' pushes up the pressures (gas) and we have consistent cycling and regular lock back on the final shot.

    I looked back at your earlier posts and didn't see any pertaining to loading, so I must assume that if you do load, you say little about it.

    I have three options for you:
    One - only shoot light to mid weight bullets.
    Two - get a 'can' so true sub-sonics with function.
    Three - learn to load and work-out your own loading that will fully function with your selected bullet weights.

    I like my 300 BlackOut, don't have or want a 'can' and my heavy weight loads are 150 grainers. The 110 V-max are nice too :D

    Hope I helped, a little.
  11. Chevelle SS

    Chevelle SS Well-Known Member

    What is a "can"?

    I don't really reload, although I help a friend of mine who does.
  12. cfullgraf

    cfullgraf Well-Known Member

    A container that soup comes in.

    Sorry, could not resist.

    A can is a suppressor, aka silencer.
  13. Chevelle SS

    Chevelle SS Well-Known Member

  14. oldpapps

    oldpapps Well-Known Member

    Mr. SS,

    Sorry I didn't make myself clear. 'cfullgraf' was more correct than he may have known. Between the First and Second World Wars, people began experimenting with various type of 'silencers'. One of the proto types that I have seen photos of was a 'tomato soup' can that had been stuffed with steel wool. From the write up it didn't work very well and the steel wool began rusting with the first shot.

    The term 'can' is given to the generic classification of a 'sound suppressor'. The 300 AAC Blackout cartridge, by its design, is very adaptable for use in a weapon that is or can be 'suppressed'. Going along with the sub-sonic abilities, the round lends it self well for use in a 'SBR'. 'SBR' being Short Barreled rifle. Theses go well together as the ATFE charges high (my opinion) fees (gun grabbers at work?) In any case, a 'can' and/or 'SBR' both require long delays as YOU are being investigated (no crime has occurred, no charges level, yet YOU are being investigated?) and your fees have been paid.

    I have no interest in either a 'can' or ' SBR', but that doesn't extrapolate that I don't care. Eroding the rights and freedoms of one is eroding the rights and freedoms of ALL.

    To the subject;
    The 300 BlackOut is what it is. Not a 1000 yards hunting round or a light 22. As I load my own, I have a greater selection of bullet weights and designs to work with and have much greater use opportunities in hunting, varminting, pest control, target shooting and general banging away. It is a fun gun with a fun round.
  15. Walkalong

    Walkalong Moderator

    I am really enjoying my .300 BLK. I think I have found a good load with the 110 Gr V-Max and 2400, although I have to re-test and see if it is repeatable. I have had a couple of good groups with the 155 Gr A-Max with AA 1680, so there is promise there. 1" to 1 1/2" groups are pretty easy to get, and that is fine for self defense.

    I do not really see the use for heavy bullets unless you want to go subsonic and use a suppressor, but who knows, if I try it I might like it. Maybe somewhere down the road I will get a suppressor for it, but right now I am having fun with 110 to 155 Gr projectiles.

    I guess the only way to know if any one .300 BLK will cycle with the heavy stuff and no can will be to try it. I do not know if the gas ports are a standard diameter on all barrels, but I do not think so. The barrel I have is an AR Stoner barrel from Midway.

    Attached Files:

  16. Coltdriver

    Coltdriver Well-Known Member

    I built a 300BLK upper just over a year ago. Got the barrel from defense industries.

    I had to take the gas port out to a tenth of an inch! A 16 inch .223 barrel has a standard gas port about .063. I progressively opened mine up to .101 as it came with the standard .063 port.

    Slightly over gassed for supersonic, worked fine with subsonic rounds. Mine would cycle the subsonics but would not lock back the bolt on an empty so it was just marginally set.

    I also put an adjustable gas block on it but ended up just opening it up. I could turn it down a bit with the supersonic if I was going to shoot those all day.

    I used the carbine length buffer weight and spring.

    As noted above use of a suppressor will increase the back pressure and "dwell" time and may let you shoot subsonic with the same settings you use for supersonic.
  17. rsilvers

    rsilvers Well-Known Member

    Sounds like either you are using too heavy a buffer, or the company who made your upper made the gas port too small, or both.
  18. bonesurf

    bonesurf New Member

    I have a different issue. Haven't tried subs, only the Remington 115gr. My setup worked fine initially, just had some issues with Lancer mags, but when I changed to pmags all fine. Ran out of ammo, didn't shoot gun for awhile. changed trigger and buffer/spring and began to get either failure to feed or double and triple fires. went back to regular carbine buffer and spring and the failure to feeds went away, but the double fires persist. Any ideas? 16" barrel.

    I am in ********** so subs and cans don't apply. Just need this thing to work well with supers. Haven't tried anything other than 115gr remington.

    Also I will be checking to make sure it's not a trigger group (disconnector) problem
    Last edited: Nov 20, 2012
  19. hentown

    hentown Well-Known Member

    Another, more serious .300 Blackout problem was brought to my attention today by a friend of mine who's a commercial ammo manufacturer. Most of friend's business is in the manufacturing and marketing of .300 Blackout ammo. However, there have been a couple of serious, catastrophic events, when a consumer inadvertently chambered a .300 Blackout round in a .223/5.56 upper. There's a long thread going on right now on ARFCOM about one of these instances.

    Seems-to-me that there's a systemic, inherent design defect, of whicy AAC and Remmy are surely aware, that's likely to result in major lawsuits....soon.

    The answer, according to my friend, is the 7.62 Wilson Combat round, which can't be chambered in a .223/5.56 rifle, regardless of one's choice of bullets for the round. All .300 Blackout rounds won't cause this problem, only the lighter bullets with certain ogives.
  20. oldpapps

    oldpapps Well-Known Member

    Give me a break!

    I wonder what WILL chamber?
    .44 mag in a 303 British.
    .308 in a 270 and others.
    Oh, yes and stick a 20 Ga into a 12 Ga.

    Ok, I've cooled down some....

    Yes, some people make mistakes and some do some stupid things and way too many people want to sue. Was your coffee Hot?


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