AR Build Question

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  • whbonney26

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    Nov 2, 2008
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    Pearl River, LA
    Edit: my barrel is 6.5"

    Okay, I have built many AR rifles but my current build is a little different than my norm.

    I built a 300 blackout pistol with onl a 6.5" barrel. The gun works well with supers and it will eject the spent rounds on the subs but don't quite get back enough to pick up the next round so it won't chamber the next round.

    I put a compensator on it and I thought once suppressed it would have enough back pressure to function properly but even with the suppressor it still is having this problem.

    I originally had an adjustable gas block but that block would not let me screw on the flash hider quick disconnect for the suppressor so it is sporting a cheap non adjustable gas block at the moment. That said, even with the adjustable one it was having those problems.

    Any idea on how I can make this gun cycle better? lower weight buffer, different buffer spring? Something else?

    Here are a few pics of the gun.
     

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    Last edited:

    twinin

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    Was the adjustable gas block having the same problems even when opened all the way? If yes, may have to do major changes

    If not, what type of buffer and spring are you running?
     

    whbonney26

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    Was the adjustable gas block having the same problems even when opened all the way? If yes, may have to do major changes

    If not, what type of buffer and spring are you running?

    I believe it was having the same issues. I put it away after I bought the suppressor and had to wait a year and two months before I get that cleared so it's been a while but I believe it was having the same issues.

    The buffer and buffer spring are mill stock any ole run of the mill. Parts that I had on hand to build with from previous builds.
     

    Bigchillin83

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    .223 ars are simple math adding and subtracting

    .300aac sub 8" barrel ars are calculus lol... those who have the formula and know how to solve the problem can do it... I can barely add and subtract :mamoru:

    i know the factory ddm4PDW ships with 2 diff springs one they suggest for suppressed subs... theres a fine line with short barreled .300... You can usually only get them to run one way good without modifications when swapping ammo... Great with subs suppressed but really over gassed with supers or Great with suppers and wont function reliable with subs

    could be gas port hole
    buffer spring
    buffer
    gas block alignment
    ect ect

    you said it will eject subs but not pick up the new round? whats the ejection angle and distance?
     
    Last edited:

    whbonney26

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    .223 ars are simple math adding and subtracting

    .300aac sub 8" barrel ars are calculus lol... those who have the formula and know how to solve the problem can do it... I can barely add and subtract :mamoru:

    i know the factory ddm4PDW ships with 2 diff springs one they suggest for suppressed subs... theres a fine line with short barreled .300... You can usually only get them to run one way good without modifications when swapping ammo... Great with subs suppressed but really over gassed with supers or Great with suppers and wont function reliable with subs
    I hear that. I really prefer it to run good suppressed with subs. That is my main concern I suppose. If it ran good other ways that would be nice but my main focus is def. suppressed with subs on this gun.

    I know they can be ran because guns like the Honey Badger use barrels in the 6" range I believe.
     

    shrxfn

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    Assuming pistol length gas. You did make sure the gas block is on correct and not leaking? If it is just a tiny bit off supers may have enough gas to make it work even with the loss whereas subs could be close to working pressure and any leakage could cause them to not function correctly. Have you tried filming the action with subs to see how bad it is undergassed? if only a little you could try lighter buffer or lighter weight BCG or just open up the gas port and go back to an AGB so you can tone it down for supers.
     

    whbonney26

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    Assuming pistol length gas. You did make sure the gas block is on correct and not leaking? If it is just a tiny bit off supers may have enough gas to make it work even with the loss whereas subs could be close to working pressure and any leakage could cause them to not function correctly. Have you tried filming the action with subs to see how bad it is undergassed? if only a little you could try lighter buffer or lighter weight BCG or just open up the gas port and go back to an AGB so you can tone it down for supers.
    I will definitely double check to make sure its on the gas port properly and maybe take a slow motion video of it in action. Great idea. Cowboy guns are my first love so sometimes I am not up to date on all the things going on in the AR world.
     

    Mr Smooth

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    Destrehan
    .223 ars are simple math adding and subtracting

    .300aac sub 8" barrel ars are calculus lol... those who have the formula and know how to solve the problem can do it... I can barely add and subtract :mamoru:

    i know the factory ddm4PDW ships with 2 diff springs one they suggest for suppressed subs... theres a fine line with short barreled .300... You can usually only get them to run one way good without modifications when swapping ammo... Great with subs suppressed but really over gassed with supers or Great with suppers and wont function reliable with subs

    could be gas port hole
    buffer spring
    buffer
    gas block alignment
    ect ect

    you said it will eject subs but not pick up the new round? whats the ejection angle and distance?
    The comment on ejection is simple to observe. It can tell things like ejector spring issues, buffer spring and buffer issues as well as under/over gassing. Is there a difference when operating in different modes?
     

    whbonney26

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    The comment on ejection is simple to observe. It can tell things like ejector spring issues, buffer spring and buffer issues as well as under/over gassing. Is there a difference when operating in different modes?
    You mean suppressed and unsuppressed?
    There is no difference or hasn't been noticable any ways.
    It does it with or with out the suppressor. Will cycle supers and eject but not cycle the next round on the subs.
     

    Bigchillin83

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    If I had to guess your subs ejection are probably dribbling out while your Supers are hitting a good three to 4 o’clock position…. Does it lock mag back on last round with supers?
     

    whbonney26

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    If I had to guess your subs ejection are probably dribbling out while your Supers are hitting a good three to 4 o’clock position…. Does it lock mag back on last round with supers?
    Well I was standing at the back of the tailgate and the spent rounds were landing various places inside the bed of the truck. The subs do not lock back on the last round.
     

    Mr Smooth

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    Well I was standing at the back of the tailgate and the spent rounds were landing various places inside the bed of the truck. The subs do not lock back on the last round.
    Are they, the empties, shooting out in front of you (1:00 o'clock), sideways (3:00 o'clock) , behind you (5:00 o'clock). It can tell alot about your rifles gas and spring condition.

    Observe the ejection pattern in different modes of operation, suppressed and unsuppressed, super sonic and sub sonic. It will assist in identifying issues or non issues
     
    Last edited:

    Magdump

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    Pistol gas guns usually are a little over gassed due to the short pathway, but that’s primarily with a 5.56 gun. I’d recheck the block and tube and also your gas key on the carrier and if that’s solid and you’re not loosing gas then maybe go to a JP captured spring set up and use the weak spring made for .300 BLK. Yeah, that’s extra money but I’ve seen it cure the issue you’re having.
    Max gas port size on a 5.56 barrel is .08” you don’t have much dwell time past your gas port, so if it’s not close to that size you’re likely under gassed. The only doubt I have about that is that running a suppressor doesn’t help. If it was low gas pressure you would think the can would fix that. I’ve never run anything shorter than 8” in .300 and prefer a 10-16” for trouble free function.
    Running a lighter carrier might make a difference but it can work both ways because inertia.
    I’ll look through my parts and weigh some buffers and see if I have a super light one and a weaker buffer spring. If you can catch me between BR and Hammond you’re welcome to them to see if they’ll work.
     
    Last edited:

    SMR412

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    I had similar issues with 8.5" 300 Blk with 220 subs, no suppressor.
    Ended up running the lighter AR15 BCG (as opposed to Full Auto M16 BCG) and removed weights from buffer. Have not a had any issues since.
     

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