short stroking a piston operated short barrel .300blk

[BreechFace]

I don't have an Adams Arms piston kit but some thoughts below:

Did you follow these instructions when fitting the gas block (specifically the measurements I highlighted in red)?
https://adamsarms.net/wp-content/uploads/2020/11/InstallationInstructions-1.pdf

It seems they ship the OP rod in the short stroke piston with the intentions of it needing to be "fit" to the rifle. With setting the gap as detailed below by Adams you will need to pay special attention that the gas port is still lining up; if not it may require removing material off the op rod to get it to within their 0.015-0.025" spec while maintaining centering over the barrel's gas port.


Note 3: It is easier to complete the remainder of the gas block installation if it is tight enough to not move
back and forth (towards or away from the receiver) unless you slightly twist the block from side to side as
you push or pull the gas block. If it moves forward or back without having to twist it, tighten it until it
requires twisting to move.


o. While you continue to hold the carrier in the receiver, work the gas block down towards the receiver
until the space between the end of the sleeve and the back part of the gas block is approximately between
.015” and .025”.
(If you continue to move the gas block down towards the receiver it will start to push the carrier down. The
rod will push on the carrier key, which will move the carrier out of battery away from the barrel extension.
If you push the carrier up into the receiver as you move the block away from the receiver the carrier will
move back into battery. You want to make sure that the carrier is pushed all the way forward against the
barrel extension and the space between the sleeve and the back of the gas block is between .015” and
.025”.)

Barrel Warning: We have experienced situations where barrel manufacturers have cut barrels out of the
commercial Mil-Spec tolerances. If the gas block will not go back far enough to get the .015” to .025” space
on the rod then the barrel might be cut out of the proper tolerance (shoulder cut too far forward). If this is the
case, you can either have the barrel shoulder cut back towards the barrel extension (receiver) or buy a
properly cut barrel.

 

[BreechFace]

If you still have issues after verifying the above I would start working with buffer weight and spring changes (reducing) and check for cycling.

As others have mentioned look for any appreciable wear on the upper receiver, bcg, piston, etc that would indicate tolerance issues causing friction in the action.

 

[Clint Oris]

I don't think it is a headspace issue at all. Or a receiver or anything else outta spec here is my thoughts and I maybe completely wrong.

Not a new issue matter of fact many users simply can't get a .300 Black to run with a Adams piston set up especially in a SBR configuration.

I would recommend that you shift it to a DI configuration and test. If that cures it then preview the following attached links if you desire to get the piston system working while getting in contact with Adams in one of the links I noticed a direct email address. Or just leave well enough alone with the DI system and use the gas piston on another project.

what is the issue??? simple the .300 black is based on a .221 Remington case coupled with a larger bore of a 30 caliber vs a .22 bore and a larger case doesn't produce the required gas volume that a .223 does. Dwell Time of a pistol vs carbine length is also working against you as well. The .300 black simply doesn't get you to pressure /volume to cycle right outta the box in the .300 Black without some adjustments in a piston setup from reports of others never attempted it myself. Usually with a 10.5 setup like you mentioned I done DI ( adjustable gas block) with mil spec components in pistol format run like a top right off the bat in both super & sub sonic loads.

Now can you get it to work?? more than likely I think you could ....will it require tinkering yea I think so.

The brass flakes you are seeing on the bolt I've seen that before with lower pressure / volume in both Semi auto's and bolt guns.
What your NOT seeing is where the rim base is contacting the bolt face it looks unfired and signs of brass flakes being compressed by bolt thrust. The case is malleable acts as a gasket when firing it starts to relax / contract /retract once the bullet passes the port. Usually in low pressure /volume you will see soot around the neck and shoulder area of the fired case almost if not to the rim. It will be dirty in the chamber and carrier as the case has NOT expanded to make a full seal. If a Case fully seals you might see a little soot around the edge of the neck. now the more you fire the chamber will dirty up with carbon but the first 20 or 30 will come out pretty clean from a clean chamber provided it has enough volume/pressure.

The DI is a overgassed setup for reliability having been around the M16/M4/ Ar15 series for over 36 years kind of versed in the setup I have only seen 1 failure a gastube had burned hole in it took less than 15 min to repair. Am I biased yes i think that the gas piston in a AR is a solution to a non existing problem. but you chose it for your own reasons which is good enough for me and I wish you the best of luck. looking over the FAQ from Adams in the "what Calibers does it work with" I noticed they had a special kit for the .300 black is that the one you have I don't know.



https://www.300blktalk.com/forum/viewtopic.php?t=95132
https://www.ar15.com/forums/ar-15/Adams_Arms_Not_Cycling_/126-690690/?
https://www.snipershide.com/shooting/threads/ar-cycling-problems-with-piston-kit.87001/
https://www.snipershide.com/shooting/threads/adams-arms-gas-piston-review.4664/
https://www.ar15.com/forums/ar-15/Adams-Arms-carbine-piston-kit-not-cycling/66-746930/
https://www.ar15.com/forums/ar-15/Adams-Arms-piston-install-question/126-763799/
https://adamsarms.net/faq/#1606556908598-09bf334f-c517
.300 black specific kit sku FGAA-03300
https://adamsarms.net/product/300blk-piston-kit-p-series-adjustable-micro-block/

I appreciate all the info - thank you.
I gave up on the idea that it might be headspace when I couldn't see any stress in the spent brass at all around the base. I took a step back for a bit tho. I was getting pretty frustrated, so I took a break. as far as the BCG goes, it is the kit that AA recommends, so I have all that covered. But, I'll dig though those posts and see if I can learn some things in there.
I originally started with 9" barrel and a handguard that had a larger ID than the OD of my fat body suppressor. The idea was that the suppressor would be covered by the hand guard and that space would still be available to mount a light and sling, etc. I found that mounting MLOK accessories, they were interfering with suppressor and defeated the purpose of free floating. But more than that was that the barrel nut for the handguard had to be machined to make clearance for the piston return spring seat and the guy that machined it had a different vision for the end result than I did.. and I wasn't comfortable with the amount of material (or lack thereof) that I was left with... so that's when I bought a hand guard from Adam's Arms that was designed to work with their piston. However, because the ID of that hand guard was smaller than the OD of my can, I had to buy a 10.5" barrel so I could mount the suppressor. That's where I landed. I still have the other upper fully assembled and I can test it out to see if that will cycle. If that does work, I'll know that a shorter barrel would be the answer (assuming I don't have a bad upper or bad BCG that is dragging and robbing energy).
I get why DI works better in this scenario - but the whole reason was to try to have less gas dumping into my face and into the receiver... so I'm not ready to give up on chasing the unicorn just yet

I don't think it is a headspace issue at all. Or a receiver or anything else outta spec here is my thoughts and I maybe completely wrong.

Not a new issue matter of fact many users simply can't get a .300 Black to run with a Adams piston set up especially in a SBR configuration.

I would recommend that you shift it to a DI configuration and test. If that cures it then preview the following attached links if you desire to get the piston system working while getting in contact with Adams in one of the links I noticed a direct email address. Or just leave well enough alone with the DI system and use the gas piston on another project.

what is the issue??? simple the .300 black is based on a .221 Remington case coupled with a larger bore of a 30 caliber vs a .22 bore and a larger case doesn't produce the required gas volume that a .223 does. Dwell Time of a pistol vs carbine length is also working against you as well. The .300 black simply doesn't get you to pressure /volume to cycle right outta the box in the .300 Black without some adjustments in a piston setup from reports of others never attempted it myself. Usually with a 10.5 setup like you mentioned I done DI ( adjustable gas block) with mil spec components in pistol format run like a top right off the bat in both super & sub sonic loads.

Now can you get it to work?? more than likely I think you could ....will it require tinkering yea I think so.

The brass flakes you are seeing on the bolt I've seen that before with lower pressure / volume in both Semi auto's and bolt guns.
What your NOT seeing is where the rim base is contacting the bolt face it looks unfired and signs of brass flakes being compressed by bolt thrust. The case is malleable acts as a gasket when firing it starts to relax / contract /retract once the bullet passes the port. Usually in low pressure /volume you will see soot around the neck and shoulder area of the fired case almost if not to the rim. It will be dirty in the chamber and carrier as the case has NOT expanded to make a full seal. If a Case fully seals you might see a little soot around the edge of the neck. now the more you fire the chamber will dirty up with carbon but the first 20 or 30 will come out pretty clean from a clean chamber provided it has enough volume/pressure.

The DI is a overgassed setup for reliability having been around the M16/M4/ Ar15 series for over 36 years kind of versed in the setup I have only seen 1 failure a gastube had burned hole in it took less than 15 min to repair. Am I biased yes i think that the gas piston in a AR is a solution to a non existing problem. but you chose it for your own reasons which is good enough for me and I wish you the best of luck. looking over the FAQ from Adams in the "what Calibers does it work with" I noticed they had a special kit for the .300 black is that the one you have I don't know.



https://www.300blktalk.com/forum/viewtopic.php?t=95132
https://www.ar15.com/forums/ar-15/Adams_Arms_Not_Cycling_/126-690690/?
https://www.snipershide.com/shooting/threads/ar-cycling-problems-with-piston-kit.87001/
https://www.snipershide.com/shooting/threads/adams-arms-gas-piston-review.4664/
https://www.ar15.com/forums/ar-15/Adams-Arms-carbine-piston-kit-not-cycling/66-746930/
https://www.ar15.com/forums/ar-15/Adams-Arms-piston-install-question/126-763799/
https://adamsarms.net/faq/#1606556908598-09bf334f-c517
.300 black specific kit sku FGAA-03300
https://adamsarms.net/product/300blk-piston-kit-p-series-adjustable-micro-block/

I appreciate all the info - thank you.
I gave up on the idea that it might be headspace when I couldn't see any stress in the spent brass at all around the base. I took a step back for a bit tho. I was getting pretty frustrated, so I took a break. as far as the BCG goes, it is the kit that AA recommends, so I have all that covered. But, I'll dig though those posts and see if I can learn some things in there.
I don't know that the barrel length is going to play a role at this point since it's a pistol length gas system (per AA recommendation and their FGAA-03300 kit) so the dwell time is always the same.I have been chasing the idea that my buffer spring is still too heavy, so I have purchased a mil spec carbine buffer and then a lightened flat coil spring - when when I measured the pressure on that flat spring, it is still heavier than the spring I'm running, so I haven't tried to run it. I can - for the sake of checking that box... however, I'm more interested in the ultra light spring that you linked. It is, however, designed for a rifle length buffer tube, so I'm guessing I'll have to cut it down for my application - which I can do at 1/2 coil increments and see if I can arrive on a working combo.

Again, I appreciate the feedback. It's very helpful!

 

[Clint Oris]

I don't have an Adams Arms piston kit but some thoughts below:

Did you follow these instructions when fitting the gas block (specifically the measurements I highlighted in red)?
https://adamsarms.net/wp-content/uploads/2020/11/InstallationInstructions-1.pdf

It seems they ship the OP rod in the short stroke piston with the intentions of it needing to be "fit" to the rifle. With setting the gap as detailed below by Adams you will need to pay special attention that the gas port is still lining up; if not it may require removing material off the op rod to get it to within their 0.015-0.025" spec while maintaining centering over the barrel's gas port.


Note 3: It is easier to complete the remainder of the gas block installation if it is tight enough to not move
back and forth (towards or away from the receiver) unless you slightly twist the block from side to side as
you push or pull the gas block. If it moves forward or back without having to twist it, tighten it until it
requires twisting to move.


o. While you continue to hold the carrier in the receiver, work the gas block down towards the receiver
until the space between the end of the sleeve and the back part of the gas block is approximately between
.015” and .025”.
(If you continue to move the gas block down towards the receiver it will start to push the carrier down. The
rod will push on the carrier key, which will move the carrier out of battery away from the barrel extension.
If you push the carrier up into the receiver as you move the block away from the receiver the carrier will
move back into battery. You want to make sure that the carrier is pushed all the way forward against the
barrel extension and the space between the sleeve and the back of the gas block is between .015” and
.025”.)

Barrel Warning: We have experienced situations where barrel manufacturers have cut barrels out of the
commercial Mil-Spec tolerances. If the gas block will not go back far enough to get the .015” to .025” space
on the rod then the barrel might be cut out of the proper tolerance (shoulder cut too far forward). If this is the
case, you can either have the barrel shoulder cut back towards the barrel extension (receiver) or buy a
properly cut barrel.

I have other piston uppers with the exact same setup (except chambered in .223W) that run well, so I'm very familiar with how they need to be set up. Also, AA had a huge lawsuit with the local SO here because of a lot of failures - piston rod sheering that would cause the gun to run full auto and dump the mag. I was very interested in the cause because I had just purchased this setup for my first build at the time, and the cause was due to incorrect spacing of the gas block from the face of the receiver. While I had properly set it up at that point (still untested) I went back through and double checked everything after understanding the consequences of complacency in this regard. What is nice with their later kits is that it comes with a spacer that puts the block exactly where it needs to be assuming a mil spec gas block journal.

 

[Clint Oris]

I had the same issue and used this, it solved the problem, 7.5" 300 blk

https://nemoarms.com/product/300-blackout-custom-carbine-buffer-spring/

might give this a try.
It sure would be nice if the complete spring specs were provided on all these different options. it's gonna get expensive (even at just $15 at a time) to buy one only to find that it's no lighter than what I'm already using.

 

[Sgt_Mike1]

I'm hoping that you really get your setup running. I am also in hopes you understand that I'm only mentioning to use the DI as a test bed to validate everything else in the build, not to abandon the concept. While I'm not a fan, I do know that many prefer the system especially suppressed. It works for them.
If we were closer together location wise I might then again might not be able to provide better insights. Easier to diagnose in person.

MY actual and original thoughts was never for you to give up on the unicorn.
I think that you can find what it will take to get it to run. just will take time