Trouble with 300Blk build...

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  • ethiojazz

    Member
    Mar 2, 2021
    12
    Hey everyone... So shoping for opinions...

    Started out with an AR15 build for a pistol version chambered in 300Blk

    I knew enough what I wanted on the lower but decided a complete upper was the way to go. Initially tried a 10.5 BCM which worked awesome but when I put a CAN on it I assumed it would even get dirtier. So decided to switch to a Pistol driven. Given my CAN length of appx 7" (JK Armament Form 1 and soon to be Omega300) I was very happy to find Adam Arms 8".

    Problem 1. Does not cycle properly... Supers work fine.. Subs not so much. Solution seems to be a change the spring to a Nemo 300 Blk seems to fix the issue.

    Problem 2. Seems that there is not sufficient barrel length to get complete burn. So not sure what can be done here except to determine what ammos will work.

    There maybe an issue with the Adjustable Gas Block but I did not want to do any exploration. I sent the upper back for factory examination since several of the settings did not seem to have any difference and there seemed to be a regulator problem but one week later I have not received any feedback from Adam Arms... That is a bit worrisome..

    So my current solution path is replace the adam arms with a POF 10.5 in piston driven upper. Will need to do some testing to determine if I can get consistent suppressed performance (I am really hoping) so I will have a reliable rifle...

    Any and all opinions and feedback will be helpful...
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    It's the Adams Arms. Dump it.(I am speaking from experience)

    Suppressed guns will run a little dirtier than un-suppressed. It's a fact of life. I don't clean mine any more than any other gun. Once every other blue moon.
     

    jrumann59

    DILLIGAF
    MDS Supporter
    Feb 17, 2011
    14,024
    I figure whether DI or Piston having an adjustable gas black would go a long way to help with cycling issues.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    Ditch the piston, 300 by it's nature has a huge range of pressures, and a piston upper introduces a lot of problems unless the engineers really did a good job on the design. Guns get dirty, with a can , a lot of that dirt is from residual gas blowing back from the bore, a piston won't stop that. Ideally a 300 gas system/buffer is properly tuned when it cycles supers without excess gas when suppressed, and reliability with suppressed subs. Most of the time there isn't enough gas to run subs unsuppressed, and it's a waste of money anyway. Pistons can be leaky anyway, and adding an adjustable gas block can loose even more gas, and subs need basically every bit of gas the round can produce. Adjustable blocks really only reduce gas, they do not increase it, very few manufacturers actually use oversized ports in 300BO, and rely on an AGB to tune it, most of the time it's a decent port size for a fixed block, and the AGB leaks enough gas to cause failures with subs. A "complete burn" is kinda misleading, you will get additional velocity up to 16" or more of barrel, subs have a different burn profile than supers, and powder / load can make a huge difference. Generally 8-10" of barrel is the "happy medium" where shorter barrels will have a lot more flash/blast and velocity loss, and longer barrels don't increase velocity much, but depending on purpose, you can justify anything from <6"-16+".
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    I figure whether DI or Piston having an adjustable gas black would go a long way to help with cycling issues.

    The main problem with Adams type systems is twofold. As the gun is fired, the op rod naturally moves rearward against the the op block on top of the bolt carrier(which takes the place of a gas key) causing the bolt carrier to move not only rearward, but upward as well. This is referred to as bolt tilt and is a bad thing. Secondly, it is also this rearward movement of the bolt carrier group that forces the unlocking of the bolt locking lugs. Brute force. This is also bad.

    In a DI BCG, the bolt unlock is aided by gas flowing into the piston chamber of the BCG(yes I said piston chamber) via the gas key that initiates the unlocking not brute force as in the Adams piston setup.

    While it is true that the Adams comes with a switch type gas block, the inequities of the system itself result, tend to result in a gun riding the ragged edge of reliability. I learned this all first hand. An expensive lesson.
     

    jrumann59

    DILLIGAF
    MDS Supporter
    Feb 17, 2011
    14,024
    The main problem with Adams type systems is twofold. As the gun is fired, the op rod naturally moves rearward against the the op block on top of the bolt carrier(which takes the place of a gas key) causing the bolt carrier to move not only rearward, but upward as well. This is referred to as bolt tilt and is a bad thing. Secondly, it is also this rearward movement of the bolt carrier group that forces the unlocking of the bolt locking lugs. Brute force. This is also bad.

    In a DI BCG, the bolt unlock is aided by gas flowing into the piston chamber of the BCG(yes I said piston chamber) via the gas key that initiates the unlocking not brute force as in the Adams piston setup.

    While it is true that the Adams comes with a switch type gas block, the inequities of the system itself result, tend to result in a gun riding the ragged edge of reliability. I learned this all first hand. An expensive lesson.

    SO basically the typical shortcomings that many piston platforms of the AR15 have.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    SO basically the typical shortcomings that many piston platforms of the AR15 have.

    Yep. Not an expert on all of them by any stretch. Mostly a problem with the conversion kits. Purpose built piston gun manufacturers have considered all the assumed drawbacks through their R&D and don't have those problems(at least not the top of the line companies).
     

    ToolAA

    Ultimate Member
    MDS Supporter
    Jun 17, 2016
    10,499
    God's Country
    It's the Adams Arms. Dump it.(I am speaking from experience)

    Suppressed guns will run a little dirtier than un-suppressed. It's a fact of life. I don't clean mine any more than any other gun. Once every other blue moon.


    My 300BO is so dirty if the lead projectile doesn’t kill em, the toxic slime that is oozing from my upper will surely do them in.
     

    ethiojazz

    Member
    Mar 2, 2021
    12
    It's the Adams Arms. Dump it.(I am speaking from experience)

    Suppressed guns will run a little dirtier than un-suppressed. It's a fact of life. I don't clean mine any more than any other gun. Once every other blue moon.


    That is definitely where I may have to go.... Thanks for the feedback... Any experience with others??
     

    ethiojazz

    Member
    Mar 2, 2021
    12
    The main problem with Adams type systems is twofold. As the gun is fired, the op rod naturally moves rearward against the the op block on top of the bolt carrier(which takes the place of a gas key) causing the bolt carrier to move not only rearward, but upward as well. This is referred to as bolt tilt and is a bad thing. Secondly, it is also this rearward movement of the bolt carrier group that forces the unlocking of the bolt locking lugs. Brute force. This is also bad.

    In a DI BCG, the bolt unlock is aided by gas flowing into the piston chamber of the BCG(yes I said piston chamber) via the gas key that initiates the unlocking not brute force as in the Adams piston setup.

    While it is true that the Adams comes with a switch type gas block, the inequities of the system itself result, tend to result in a gun riding the ragged edge of reliability. I learned this all first hand. An expensive lesson.


    My observations definitely have not even gotten to the BCG tilt. I am assuming that was why the company made the BCG lighter. I was concerned this would be a bigger problem in Supers and not as much on Subs..
     

    ethiojazz

    Member
    Mar 2, 2021
    12
    My 300BO is so dirty if the lead projectile doesn’t kill em, the toxic slime that is oozing from my upper will surely do them in.


    Hahahaha... I appreciate the backup that 300BLK provides but was hoping to take advantage of the silent rock throwing (heavier bullet)
     

    ethiojazz

    Member
    Mar 2, 2021
    12
    Ditch the piston, 300 by it's nature has a huge range of pressures, and a piston upper introduces a lot of problems unless the engineers really did a good job on the design. Guns get dirty, with a can , a lot of that dirt is from residual gas blowing back from the bore, a piston won't stop that. Ideally a 300 gas system/buffer is properly tuned when it cycles supers without excess gas when suppressed, and reliability with suppressed subs. Most of the time there isn't enough gas to run subs unsuppressed, and it's a waste of money anyway. Pistons can be leaky anyway, and adding an adjustable gas block can loose even more gas, and subs need basically every bit of gas the round can produce. Adjustable blocks really only reduce gas, they do not increase it, very few manufacturers actually use oversized ports in 300BO, and rely on an AGB to tune it, most of the time it's a decent port size for a fixed block, and the AGB leaks enough gas to cause failures with subs. A "complete burn" is kinda misleading, you will get additional velocity up to 16" or more of barrel, subs have a different burn profile than supers, and powder / load can make a huge difference. Generally 8-10" of barrel is the "happy medium" where shorter barrels will have a lot more flash/blast and velocity loss, and longer barrels don't increase velocity much, but depending on purpose, you can justify anything from <6"-16+".


    Thank you so much for your feedback... So your analysis was what let me to basically three decisions... 1. I assumed getting a complete upper would allow me to take advantage of the companies experience and updated process so that it would be clear how to adjust the firearm for different ammo... Eventually I want to be able to do my own loads but I am assuming that will be even more tuning... Which is why I picked the Adam Arms upper.. AGB had more than two settings etc.. 2. While I would have preferred a 10" barrel I assumed the 8" plus the can would provide both the length to get max burn and provide required pressure both to provide reliable action and max speed..

    But I am now questioning all of my logic....
     

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