AR15 300 Blackout Cycling Issue

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  • Donald1818

    Active Member
    Aug 22, 2013
    351
    Baltimore
    So I am aware that the 300BO has cycling issues.

    I took mine out this weekend and had a lot of fun with it.
    REALLY -- A lot of FUNN!!!
    Actually I got my first Buck (EVER) with it, even with it's issues.
    --
    So my question it thus.

    In regards to the AR's Buffer spring. I am not seeing any kind of differential between springs on the Interweb market.

    Is there a compression rating?
    Is there a load rating for buffer springs?

    I am not even sure what word to use to express my question comprehensively.

    I see buffer springs, price wise, from $3 to $50. but no comparative information associated with them.

    I guess what I am asking is, for the 300BO users here on this forum, what kind of buffer spring are you using, and how are you determining a value to that spring to get your AR to cycle effectively.

    A thought that I had was simply this, to buy two or three regular springs and cut some of the end off until it cycled properly. But I thought Id ask the general population this question first, before bothering with that task.

    I shot about 30-40 rounds and not one fully cycled.

    At the moment I am assuming that the problem is the spring but I know that there are a few other contributing factors that could cause the 300BO AR15 not to fully cycle. this is just my first attempt to solve the issue.

    I used two different bullet weights, 125 and 150 GR Green nosler polymer tipped.
    And 150GR FMJ.
    The casings were made by me, from .223
    The powder loads were H110 15GR.
    I got the load recipe off YOUTUBE.

    Thank you for reading this post.

    Don
     

    jimbobborg

    Oddball caliber fan
    Aug 2, 2010
    17,112
    Northern Virginia
    How much lube on the BCG? And how long is the spring? I've had cycling issues on the same rifle, once was due to installing an AR-10 spring and once was due to lack of lube on the BCG.
     

    Donald1818

    Active Member
    Aug 22, 2013
    351
    Baltimore
    If by lube you mean gun oil, I oiled it up enough that while shooting it this weekend it pretty much oozed out all over the place.

    How long is the spring? I have no idea.

    I would have to take it apart and measure it.

    Do springs come at different lengths?

    IF they do I have not noticed any kind of data regrading that spec on ANY of the web pages that I have visited.
     
    Last edited:

    HokieCasey

    Active Member
    Aug 7, 2010
    834
    St Mary's
    first thought is that your load is too light for a semi-auto action. Did you properly develop the load prior to rolling out to hunt? or did you load up X number of rounds?

    Based on the books and loads I have found 15 grains of H110 is probably not enough to properly cycle an AR15.

    So I would check your load development and consider reevaluating your powder load, especially for the 125 grain bullet.
     
    Last edited:

    Donald1818

    Active Member
    Aug 22, 2013
    351
    Baltimore
    deer

    deer
     

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    Russ D

    Ultimate Member
    Nov 10, 2008
    12,029
    Sykesville
    The round does not inherently have cycling issues. Guns of all calibers have cycling issues but well built .300 BLK don't have cycling issues. Gas port size is key which is why I built on a Noveske barrel.
     

    Mdeng

    Ultimate Member
    Industry Partner
    Nov 13, 2009
    8,568
    Virginia
    I had a problem with mine when I first started shooting it. Check to make sure your gas block hasn't moved. Is it pinned or is it held by friction or set screws? Once I sent my upper back to the manufacturer to have the gas blocked pinned I haven't had another problem.

    Oh and I will add. Never take load data from YouTube! Use load Data Books published my component manufacturers!
     

    Donald1818

    Active Member
    Aug 22, 2013
    351
    Baltimore
    This is the first for everything for me.

    I have no baseline for determining what a proper load is.

    I do not know what the proper loading tolerances are for this load.

    I found some youtube video that informed me that that load worked for him and went with that.
    I am still learning.

    I do not know what the casing will or could handle as far as load value, = more Grains of powder.

    For a noob, it sent the bullet A-Flying, but didnt recycle, so I was half the way there.

    Thanks for your values.

    If anyone else out there has "recipes" for a similar load please let me know.

    As I was shooting it felt weak.
    I had shot in a different upper in .223 and the power was noticeably different.
    My hand loading of .223 loads were 25GR of powder.
     

    ride4frnt

    Active Member
    Jun 18, 2011
    955
    Clear Spring
    I had cycling issues with mine that I couldn't pinpoint for over a year. Took the barrel and gas system apart, rebuilt it. Myriad buffer/spring combos. Nothing at all worked.

    My problem was it would fire the first round, chamber the second, but the second round would not fire.

    One day I switched my .300 upper onto a new lower and it ran flawlessly.

    What was happening was it was clambering the first round, and after the first trigger pull the disconnector wasn't locking the hammer back. Apparently my kns pins or spikes battle trigger were out of spec. Nonetheless I switched to milspec pins and she runs flawlessly.

    Fwiw, I run a spikes t2 buffer and a Wolff xp spring on a 16" noveske pistol length gas system.
     

    HokieCasey

    Active Member
    Aug 7, 2010
    834
    St Mary's
    check IMR's site for some load recommendations from the Powder manufacture.

    or better yet buy a reloading book that has 300 blackout in it.
     

    Donald1818

    Active Member
    Aug 22, 2013
    351
    Baltimore
    I appreciate the loading info.

    For me this was my first attempt.

    I did not have any reliable source of loading data last week.

    If any of you can contribute actual experiential data that would help me.

    Thanks
     

    Mdeng

    Ultimate Member
    Industry Partner
    Nov 13, 2009
    8,568
    Virginia
    If your new to reloading you may want to pick up a booke called "The ABC's of Reloading" published by LEE. There are many things that can go wrong if you fire a cartridge with to much or to little powder.

    Don't use experimental load data! Use only published data from reliable known sources, such as powder and bullet manufacturers.
     

    rsilvers

    Active Member
    Dec 24, 2010
    113
    300 BLK has no cycling issues if you for example buy an AAC brand upper or rifle, or one that works as well.

    All 300 BLK uppers use a normal Colt M4 spring.

    The buffer needed depends on what the barrel was designed to use. I read and re-read your post. I could not find what brand rifle you have so I can't tell you what your barrel was designed to use.

    If it is an random brand or home-made barrel, then maybe the gas port is too small. You won't run into that on proven brands.

    And it could also be a leak in your carrier-key or gas block. Or your gas block could be rotated or not aligned with the gas port.
     

    Donald1818

    Active Member
    Aug 22, 2013
    351
    Baltimore
    It is a personal build.
    I know that there could be more issues than just the spring, I was starting with what I thought might be the easiest problem to solve, I had read in other places that 300BO builders were having spring problems, and they switched it out and then their builds worked.
    Thanks.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    One thing I can say with some experience, 15gr's of H110 is too light to fully cycle the action with a 125gr round, and is still a bit light even on a 150gr round.

    W/out going thru my load log, I believe I was into the low to mid 16gr range before it'd cycle with 150gr rounds thru a 16" Noveske Pistol-length gas system.

    Honestly, I'd suggest ponying up and getting some factory supersonic ammo to really see if the rifle has a true cycling issue. If it won't run the factory 125gr load, then it's got an issue somewhere.

    If it does cycle it, then you need to start bumping up the charge weight some gradually.
     

    johnhmpg

    Active Member
    Mar 14, 2011
    351
    First I would see if your gas port is aligned. Plug chamber with finger. Blow down barrel. If you feel unrestricted air flowing out of the gas tube you're probably good. Next go buy a box of factory ammo. Test with it. Freestate probably has some in stock and you can shoot it there.
     

    pwoolford

    AR15's make me :-)
    Jan 3, 2012
    4,186
    White Marsh
    One thing I can say with some experience, 15gr's of H110 is too light to fully cycle the action with a 125gr round, and is still a bit light even on a 150gr round.

    W/out going thru my load log, I believe I was into the low to mid 16gr range before it'd cycle with 150gr rounds thru a 16" Noveske Pistol-length gas system.

    Honestly, I'd suggest ponying up and getting some factory supersonic ammo to really see if the rifle has a true cycling issue. If it won't run the factory 125gr load, then it's got an issue somewhere.
    If it does cycle it, then you need to start bumping up the charge weight some gradually.

    I was going to suggest this also. If factory loads don't cycle then I'd try a different buffer. I run the Spikes T2 in my 300 and it cycles great.
     

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