My piston rifle...under gassed.

[db_17_85]

All,

So here's what's up... I just built a new 5.56 rifle with 20" WOA SDM barrel and rifle length Adam's Arms piston. Buffer is just a standard rifle weight. I was having unreliable cycling with 5.56 pressure and so switched to some known low power ammo (Tula). The switch confirmed that she is behaving under gassed. The Tula wouldn't even fully extract. The 5.56 would generally extract but not always feed. Any ideas from the Hive?

 

[Powder_Burns]

Re: My piston rifle...under gassed.

I'm not familiar with the gp setup, but does your carrier still use a bolt cam pin? Assuming this is a new gun, does it feel like theres an awful lot of friction there if you try to cam the bolt by hand? Sometimes tolerance stacking is the main issue, some parts need to be broken in and lubed well..

 

[Snake Plissken]

Re: My piston rifle...under gassed.

Get an H2 buffer, those are usually the standard for Piston ARs.

 

[Tangodown911]

Re: My piston rifle...under gassed.

I was having a problem with 12" piston LMT MRP short cycling. I was running an H2 buffer. Called LMT and they suggested a H buffer. Waiting on it to come in then I'll try it. Since your are running a standard buffer then I would say it's a FSB/gasblock alignment issue. Not sure if you have checked that, but that's what I would look at first.

 

[Tangodown911]

Re: My piston rifle...under gassed.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Snake Plissken</div><div class="ubbcode-body">Get an H2 buffer, those are usually the standard for Piston ARs. </div></div>

Who recommends this? Which Manufacture?

 

[db_17_85]

Re: My piston rifle...under gassed.

Snake,

The H2 would work if I was over gassed. Unfortunately, I have the opposite issue.

Powder,

No real friction. In fact, the Adam's comes with a spring that goes behind the bolt. The carrier will actually poke out when I open the receiver. As for alignment, there is no binding in the piston movement at all and all adjustments were made in accordance with the instructions. May have to take the block off and take some measurements to ensure alignment with gas vent in barrel though.

I've actually been thinking about trying a JP LMOS buffer. Not sure yet though.

Thanks for all the ideas guys, keep 'em coming!


db

 

[jwp6114]

Re: My piston rifle...under gassed.

some may not agree on it at all but i have seen that a good quick fix for short stroking is to use a lighter buffer spring or cut a couple coils off...

if you have play'd with buffers then try lightening up the spring.

it has work'd for me getting a few 10" gas guns to run right and reliably...

 

[JMC]

Re: My piston rifle...under gassed.

Your options are to reduce operating weight of moving parts or to increase the gas available. (if you want to stay with the Adams piston)

You can reduce the carrier weight (not an easy option), reduce buffer weight such as an "H" or the standard carbine buffer, or to reduce the spring pressure on the recoil spring - I wouldn't recommend cutting coils as a long term fix but you could clip a few coils to try it but a better option as is getting a reduced strength spring such as Wolffe.

Your other option is to increase the gas port opening also and have it reamed to a slightly larger size but the change will be very slight so don't go too much.

Good luck
JMC

 

[frankythefly]

Re: My piston rifle...under gassed.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tango__Down</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Snake Plissken</div><div class="ubbcode-body">Get an H2 buffer, those are usually the standard for Piston ARs. </div></div>

Who recommends this? Which Manufacture? </div></div>

LMT recommends this on piston systems for 16 inch barrels. They supply the rifles with them(H2) pre-installed or with the piston kit. going to a lighter buffer would work.

What you could do is tap out the roll pin on the buffer and take a weight or two out. Give it a try. You will find it usually extra noisy because of the weights moving back and forth. However I have used very small amount of steel wool in rolled up balls to dampen the noise.

I would start out removing 2 weights, then remove one at a time until it functions right. If it doesn't function then you have something else going on. Perhaps the gas port or regulator needs to be cleaned.

 

[db_17_85]

Re: My piston rifle...under gassed.

JMC,

I sincerely hope I don't have to open up the gas port. I have faith that WOA did it right and I am the first time I've ever heard of an under gassed Adam's. First for everything though!

Franky,

I may look into this tonight. Hopefully there is more than 1 weight in a standard rifle buffer. As for cleaning, today was the first time she's ever gone bang! (Just got it finished...)

 

[jwp6114]

Re: My piston rifle...under gassed.

man i could understand having such issue with a 10" sbr, but a 20" should have plenty of dwel time to build enough pressure to function.

call me ignorant but i have never been a fan of piston conversions...

 

[db_17_85]

Re: My piston rifle...under gassed.

I gotta admit, this one is blowing my mind. I've heard of needing to slow down the cycle speed after a piston install, but NEVER have I heard of it being too slow. As for the piston itself, I went with it for 2 reason:

1. I like pistons.

2. I want to do a test... Run a well built rifle for a while with a piston and see exactly what she is capable of. Then, switch the SAME rifle over to DI and see if there are any accuracy gains. Everyone says that piston = less accurate but I've never seen a test using the exact same rifle to prove one way or another. An expensive test...yes. But worth it to me and hopefully the hide will enjoy it.

 

[JMC]

Re: My piston rifle...under gassed.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: db_17_85</div><div class="ubbcode-body">JMC,

I sincerely hope I don't have to open up the gas port. I have faith that WOA did it right and I am the first time I've ever heard of an under gassed Adam's. First for everything though!

Franky,

I may look into this tonight. Hopefully there is more than 1 weight in a standard rifle buffer. As for cleaning, today was the first time she's ever gone bang! (Just got it finished...) </div></div>

Opening up the gas port would be my last resort. I'd try lightening the moving weight and spring tension on everything I could before I did that. Start with the cheapest and easiest to replace parts first.

Also, did you call Adams Arms and see what they had to say?
JMC

 

[JMC]

Re: My piston rifle...under gassed.

Also try changing the bolt head if you have a spare. At the armorers course I was at the instructor had said he had a gun that he couldn't get to run (DI) No mater what he did. He found it turned out the locking lugs were cut slightly out of spec but looked fine. He said a different bolt and ran great.

JMC

 

[db_17_85]

Re: My piston rifle...under gassed.

I do have another matched bolt. I'll try the weights first, and then the bolt. Hopefully I'll be able to get out and shoot it again tomorrow. If I can't fix it after those, I'll be contacting Adam's to see what they have to say. Once again, thanks JMC.

 

[callen3615]

Re: My piston rifle...under gassed.

Are you sure the gas port is lined up with the gas block? Maybe its undersized.

 

[db_17_85]

Re: My piston rifle...under gassed.

As sure as I can be without removing the block and taking measurements. I hope it doesn't come to that, but my micrometer is ready if it does.

 

[KevinB-KAC]

Re: My piston rifle...under gassed.

You can't properly Mic a gas port (especially on a piston gun as they will be smaller than DI) - you need to pin guage it.

 

[db_17_85]

Re: My piston rifle...under gassed.

Good to know Kevin. A question on getting the buffer lighter... If I remove a couple of the weights, do I need to add something of comparable size to keep the remaining weights from gaining extra momentum? I picked up some aluminum round stock already, but figured it can't hurt to ask.



a quick edit...my mic comment was in regards to alignment, not gas port size. Still good info to know however.

 

[jwp6114]

Re: My piston rifle...under gassed.

most of the time at least in DI guns all of the gas block holes are quite larger than the hole in the barrel so it would be quite obvious if it were misaligned. if you can choot a few rounds 5 or so, take the gun apart look at the gas hole on the barrel, there will be a black ring around it the size of the gas block hole... a bit larger than the barrel hole. and this will show you how aligned it is. desnt have to be centered.

if i was a fan and super familiar with the piston conversions i would say send it to me and i'll get it running right for ya at no cost other than shipping, i build at least a dozen gas guns a year... sbr's and otherwise. some of the sbrs are tricky to get to run right and reliable.

there are some other tricks like polishing several of the parts that slide over each other to lessen drag in the gun...I.E the hammer and botom of the bolt and a couple others but their kind of trade secrets in my book. knowledge is valuable to me. but i will help as best as i can in most cases.

Should you be having these issues in the first place? NO... if i ware adams arms i would take the gun in and right it at no charge... Im a big fan of manufacturers that stand by their product, even if its just there installation guide left something out.

 

[db_17_85]

Re: My piston rifle...under gassed.

An update:

I removed two weights from the buffer last night an inserted an aluminum spacer I made to be the same length as the weights. She still doesn't like Tula (it's a great way to test how your rifle will run on low pressure) but she ran like a top with everything else. Recoil is a dream. I'll get some pics of the rifle tonight hopefully. I still plan to check the gas port and alignment, but at least now I have a running rifle. A big thanks to everyone who helped out!

 

[rsilvers]

Re: My piston rifle...under gassed.

Removing weight is a bad idea as the buffer weight is for a reason. The gas port is up to the rifle maker to correctly set.

This does not have enough gas. You should get the correct gas port size from Adams Arms. Or select it yourself using high speed video for bolt carrier velocity or other method.

 

[rsilvers]

Re: My piston rifle...under gassed.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: db_17_85</div><div class="ubbcode-body">Recoil is a dream. </div></div>

That is because you are still under gassed. You should put the weights back and fix the actual problem.

 

[db_17_85]

Re: My piston rifle...under gassed.

rsilvers,

I do plan on getting it fixed right. That is what I meant by " I still plan to check the gas port and alignment,". However, I need this rifle for an upcoming trip and having it running is better than at Adam's or WOA. Once I return, I will pin gauge it and go from there.


On a side note... I realize that under gassed can cause reliability issues when the action is fouled, but how is it different that the guys who run adjustable gas blocks and dial down to run LMOS systems at bare minimum gas? I'm honestly not trying to be a dick... I'm am very familiar with the AR, but I have no doubt that you are more familiar with the tweaking than I am.

 

[moagm316]

Re: My piston rifle...under gassed.

I had an idea to do a similar build. Did you ever get pics up?

 

[db_17_85]

Re: My piston rifle...under gassed.

Holy zombie thread....

As for the pics...

www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Main=279000&Number=3165524#Post3165524

 

[smschulz]

Re: My piston rifle...under gassed.

FWIW, I have an almost identical build.
I had the same problem initially too.
My resolution was to:
a) slightly enlarge the gas port
b) use a Wolff reduced power buffer spring
c) Endine buffer

Note: this was in a PRS stock.
I think the enlarged port and the buffer spring were the main things that helped.