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pukindog
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Posted: 4/19/2012 10:55:58 AM
Anyone using a piston on a pistol length gas system?

My 7.5-inch barreled pistol is kind of ammo picky when it comes to adequate pressure to cycle it. It is not nearly as reliable and flexible as I would like it to be and I am looking for options including the possibility of a piston system.

I'd like to hear about experiences - good, bad or otherwise.
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skyungjae
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Posted: 4/19/2012 11:10:19 AM


YHM Lower Receiver
Rainier Arms Upper Receiver
Rainier Arms 7.5" Barrel
Magpul MIAD Grip
Magpul MS2 Sling
Matech rear BUIS
Midwest Industries front BUIS
POF roller cam pin
Adams Arms PDW length gas piston
Adams Arms Samson 4" Rail
Spike's Tactical ST-T2 Buffer
BCM Extractor Spring Upgrade
Ergo Grip ladder rail panels
GG&G Accucam Quick Detach
Trijicon Reflex RX-06

When I first put this together two years ago, I had trouble with extraction on my first range trip. AA customer service was very helpful in identifying the problem. After upgrading the extractor spring and adding the o-ring, it has run flawlessly for over 1000 rounds. I've shot various 55gr ammo out of it like Federal, PMC, AE, etc. I haven't shot much steel cased ammo out of it, because the range I go to doesn't allow bi-metal projectiles. I know there are a lot of people who are against piston systems on ARs in general, but find them acceptable when it comes to 7.5" SBR/Pistols.
pukindog
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Posted: 4/19/2012 11:42:08 AM
Thanks for the response.

I had to do the same extractor upgrade to make my DI pistol function. That kind of tells me that there's little or no difference in that particular issue regardless of which gas system is used. I believe that issue stems from the short gas system leading to the gun trying to cycle before the round in the chamber has contracted enough from it's expansion upon firing. The extractor has to be stronger to pull the round out. Sorry, I am no scientist and probably didn't explain that well.

I guess the question I am looking at is will a piston system cycle with lower pressure than DI, or does it take every bit as much pressure, or maybe even more?

For what it's worth I am certainly not opposed to piston systems. I have an AA kit on one of my carbines and I am very satisfied with it.
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ABNAK
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Posted: 4/20/2012 2:51:02 AM
I made my S&W MP15R (5.45x39) upper into a pistol. Granted, it's an 11" barrel and not uber-short like some of you guys have. I have an Osprey piston system on it. The 5.45 operates at a lower pressure than 5.56 to begin with so we had to open the gas port a smidge as well as cut a few coils off the buffer spring (using a standard weight buffer too). Now it runs like a top! Every now and then it won't lock back on an empty mag but I can live with that; it's certainly not over-gassed and function is fine.
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pukindog
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Posted: 5/1/2012 1:32:25 PM
Originally Posted By ABNAK:
The 5.45 operates at a lower pressure than 5.56 to begin with so we had to open the gas port a smidge .


Can you define a smidge? Just curious about the gas port size you ended up using.

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fatkid_mayfield
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Posted: 5/1/2012 2:58:10 PM
I have built a couple of different 7.5" uppers with AA kits and haven't had any issues with cycling. My 5.56 builds I have tested with crap to black hills ammo with out issue. I also built one chambered in 7.62x39 that functioned with milsurplus flawlessly.



Fatkid
ABNAK
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Posted: 5/1/2012 3:23:23 PM
Originally Posted By pukindog:
Originally Posted By ABNAK:
The 5.45 operates at a lower pressure than 5.56 to begin with so we had to open the gas port a smidge .


Can you define a smidge? Just curious about the gas port size you ended up using.



Honestly? We used the next size up drill bit from the one that fit in the hole snugly. I know it's not scientific by any means but evidently wasn't too much as we still had to cut a few coils from the buffer spring after that (didn't want to play around with opening it up any more than we already had).

Ask not what you can do for your country, ask what your country the taxpayers can do for you".

11C2P '83-'87. AIRBORNE INFANTRY!!!
Paul_HoganGuns
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Posted: 5/1/2012 3:30:12 PM
Im just going to leave this here.

http://www.hoganguns.com/videos/videos.html
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pukindog
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Posted: 5/2/2012 9:20:23 AM
Originally Posted By ABNAK:
Originally Posted By pukindog:
Originally Posted By ABNAK:
The 5.45 operates at a lower pressure than 5.56 to begin with so we had to open the gas port a smidge .


Can you define a smidge? Just curious about the gas port size you ended up using.



Honestly? We used the next size up drill bit from the one that fit in the hole snugly. I know it's not scientific by any means but evidently wasn't too much as we still had to cut a few coils from the buffer spring after that (didn't want to play around with opening it up any more than we already had).



I have essentially done the same thing with mine as far as the gas port is concerned, and will test it out this weekend.

Still not sure if I will put a piston kit on it, but fatkid's post above is encouraging.
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pukindog
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Posted: 5/2/2012 9:21:03 AM
Originally Posted By Paul_HoganGuns:
Im just going to leave this here.

http://www.hoganguns.com/videos/videos.html


Well that was fun watch !
I ain't here for a long time. I'm here for a good time.