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Thread: 300 blackout feeding.

  1. #1
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    300 blackout feeding.

    There were some good deals i got lined up recently, and lo and behold I ended up with a new gun. Its a 7.5" 300 blackout pistol with a shockwave blade, anderson lower, Grizzly armament complete upper (bcg/charging handle). Leupold freedom rds, all said and done I have $500 into it.

    So i picked up some armscor 147gr fmj, loaded some 110gr hornady vmax, and some hornady 150gr fmj.
    For powder I am using Accurate 1680 for the 110gr, and I just tried it with the 150gr when I was working on my issues (gun issues, will get to them).
    I started using the 150gr hornady with Accurate #11fs (supposed to be designed for this cartridge).

    So, the 110gr vmax runs extremely well, absolute blast to shoot. The Armscor ammo doesnt cycle the action, it ejects the spent case, but does not load the next cartridge. On the last round it does not hold the bolt open. It is going back far enough to reset the hammer. The 150gr handloads with 11fs are doing the exact same thing. If I load with 1680 the 150gr it runs great.
    So from what I understand, where my brass lands is going to tell me how im gassing? The factory ammo lands at 3oclock, the 1680 lands at 4oclock. Had a brass catcher on previously, so dont know where the vmax or 11fs lands
    Catagorized for clarity.
    147gr armscor - FTF
    110gr vmax 1680 - works
    150gr #11fs - FTF
    150gr 1680 - works.

    I tried multiple different magazines.

    Most likely the armscor is using either 11fs or Hodgons CFEblk (which as western powder is now owned by Hodgons, i suspect they are extremely similar if not the same?).

    The obvious thing is what powder works and doesnt. Im not a AR expert, will changing the buffer, spring, or putting a adjustable gas block in fix my issue? Its a pistol length buffer tube with whatever buffer and spring came with it.
    The 1680 in this cartridge is supposed to be best for subsonic loads, while the 11fs is supposed to be best for supers.




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  2. #2
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    First thing to do is make sure the hole in the gas block is properly aligned with the gas port in the barrel. While you have the gas block off I would measure the diameter of the gas port in the barrel. 7.5 inch barrel is not going to give you much dwell time and a adjustable gas block isn't going to do you any good if you gas port is already undersized. There are -10 power springs available and depending on what weight buffer you have you could swap that but most likely your gas port needs to be opened a bit.

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  4. #4
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    Removed the handguard and slid the gas block foreward, i do not have a device for holding the barrel to remove the muzzle brake (reaction rod?), so did not completely remove the gas block. So was not able to see the gas port on the block, I did measure the gas port on the barrel, it measures .1". Barrel diameter for the block is .750". Without being able to measure how far recessed the gas port on the block is, i was only able to verify the side to side alignment, not depth, i slid it back on so it is flush with the larger diameter machining on the barrel (same place that it was set from the factory). Ran 5 shots through it this morning with the arsmcor ammo, still same ol' ftf issue.

    I measured the weight of the buffer, on a kitchen scale I am getting between 3.0 oz and 3.05 oz. Measured the weight of the buffer from my 458 SOCOM (came with the carbine length tube), it weighed in at 3.05-3.1 oz. I installed it in the 300, test fired with the armscor ammo, ran through the five rounds I loaded without a hiccup. It did not however lock back on the last round.

    I disassembled the original buffer for the 300, did some careful measurements, there are 3 steel pills in it, each weighing in at 300-305 grains. The seperating pads were about 6 grains. I just so happened to have a 90 grain tungsten disc that actually fit quite well in the stack if i removed one of the seperating pads. No more of that baby rattle from the buffer now to! On the kitchen scale the modified buffer weighs in at 3.2oz.
    It ran through 5 shots great on a hexmag. It did not hold open on the last shot. Ran 10 more through a pmag, it held open on the last shot. Will do some further testing to see if the brand new hexmags are garbage (they do hold open on the 1680 handloads).

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    Most gas blocks have the first set screw even with the position of the gas hole in it. If you spin the gas block around 180 degrees and push the gas block back to the shoulder on the barrel it will show you how you are lining up with the port. Some barrels are cut expecting a hand guard retaining plate between the gas block and barrel shoulder so you might be off by a bit. Most people have issues running subs not supers and a gas port of .100 should work for supers unless you are running some very weak loads.

  6. #6
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    ditch the hex mags here is me experience with them.
    from their web site
    https://hexmag.com/browse-by-caliber
    SENTRY’s Hexmag line of firearm magazines feature an iconic HEXTURE™ design pattern and are engineered to be one of the most versatile magazines on the market. SENTRY’s line of AR15 magazines is regarded by shooters worldwide for their dependability, durability and distinctive looks. Not only are these AR magazines compatible with most every 5.56x45 NATO, .223 Remington round but also several other calibers that are gaining in popularity. Those that have AR15’s chambered in heavy duty rounds like .300 AAC Blackout, .458 SOCOM and .50 Beowulf look to SENTRY for your magazine solution and keep your firearm fed.
    so thought I would give them a try guess what...
    as I sent them a reply
    from me

    QUOTE I recently purchased two of the 30 round hx-ar series 2 magazines at a local gun shop, you have these listed as working with 300 aac blackout... after loading in about five rounds it became harder and harder to load rounds, in fact I could push a round down as far as I could and could get at least two more rounds in, as the follower was bound up by the rounds pushed down in the mag. this was the same with both magazines, this I tried with several different brands of 300 AAC and many different weight bullets, all factory rounds. I doubt they would be reliable for 300 aac any suggestions?
    quote
    and lets not forge the and I quote
    Warranty Information

    Magazines purchased from an Authorized SENTRY Distributor, Dealer or SENTRY Direct are fully warranted to the original owner against defects in materials and manufacturing processes.
    (Proof of purchase may be requested).

    IF OUR PRODUCT NO LONGER OPERATES AS INTENDED, SENTRY WILL REPLACE OR REPAIR IT WITHOUT CHARGE TO THE ORIGINAL OWNER.*
    I figure give them the benefit of the doubt low and behold they reply (wow way to stand behind your product)

    Thank you for contacting SENTRY Products Group! Unfortunately we have had some issues with the .300 aac because of the overall length of the cartridge. My suggestion would be returning them to the store you bought them from if you can. I’m very sorry for the inconvenience. Please let me know if there is anything else that I can do for you.



    Thank you,



    Adam
    Customer Service Representitive


    but wait there is more


    they also said

    hexmag: I understand your frustration. Our magazines will work with .300 AAC as long as it is not loaded to max overall length.
    me: hello they were all factory rounds...

    hexmag: However, you will not be able to put 30 rounds of .300 AAC into the AR15 magazine, it should only fit about 8.

  7. #7
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    Will do some further measurements on the gas block, makes sense from a manufacturing standpoint on where you could drill the gas passage in it.

    The 8 round limit is absolutely rediculous and unacceptable! Was planning on haveing this gun in a convenient location for home defense and coyotes and whatever else needs shot in a hurry, will probably be using pmags for that. Curiosity may lead me to trying out the hexmags in the socom, if anything should make them fail, that should. Havent ever had issues with that, so would be quite telling (only ever used pmags, usgi, and torkmag in it.before). I picked up the hexmags because they appeared to have enough space for longer projectiles (some mag brands dont work with the 325gr ftx rounds in my socom because they are to short on the inside. The hexmags have more space.
    If all else fails and the hexs are absolute garbage I'll prolly turn them over to my brother who has a 5.56 and see if they work for that.

  8. #8
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    Did a brief search, lots of advertising garbage on the hexmags, seems they love to pat their own backs on that they figured out how to change the magazines colors. Im impressed to. Seems from my brief search people have varied results with all mags. Me personally i thought the hexmags felt like garbage compared to my other brands. Thats just perception however. Bought the hexes and the pmags for $10 each... so guess i shouldnt expect the world from that.

  9. #9
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    So are you using 300 BLK OUT mags or 5.56X45 maps? I run subsonic ammo in my 300 BLK OUT upper. I bought some BLK OUT specific Magpul magazines. I have had no feeding issues using those magazines.

    Scott

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    I have Daniel Defense mags that are designed to work with both 556 and subsonic 300.

    Havenít had a single jam either semi or fullauto in 1k rounds of 220grn subsonic through 5 of their mags.


  11. #11
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    As I recall when I researched it the 300 BLK specific mags were meant for feeding subsonics.

    If you are doing 110g to 150g bullets, regular magazines should do you just fine. I use standard GI mags, some Magpuls but my favorite is Lancers. Lancers are my go to magazine. I've never used Hex Mag.

    As I have found from loading 300 Blackout for almost a decade now, there are a limited range of powders to play with and from that list, some are more optimum than others.

    I've loaded many thousands of Hornady 150g in 300 BLK and after experimenting, I think Lil Gun works best.

    I did a whole 4 part Youtube series on my Channel on loading 150g Hornady FMJ bullets in 300 BO. Same user name.

  12. #12
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    Yeah, the subsonics seem to be the issue everybody is haveing. I havent loaded subs yet, as i havent picked up a flash hider that attaches to a can yet. I picked up som magpull 300 BO mags. Didnt notice any change with lockback (only issue i am having now). I ran a mag of 400 gr 458 socom through a hexmag... worked great. So dont see why they would have a issue with a lighter cartridge/projectile.
    Havent messed any farther with the gas block yet. May still end up getting a adjustable.

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