Looking for a Piston Driven A.R.

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My God that's a big picture!!

I have no idea what I am typing on my ipad because the hemungus picture shrinks the text to nearly microscopic.

Please resize it to forum guidelines!

rc
 
Sorry RC, it won't let me edit it. It's been too long. I didn't notice it when I posted because I left the thread for a month or so.. Apologies.


To everyone knocking the piston system, please respect the OP's post. He asked for a piston gun. It isn't our place to judge. Either help him on choosing a piston system, or drop it. It isn't about weather we like piston or DI rifles better. It is about him asking which piston he should look at.

Just my $0.02. Everyone wants to change people minds instead of helping do what they ask.
 
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Your post made me chuckle Charlie. I once posted a question seeking some advice about getting a Beretta 92 or 96. I was so disappointed when 90% of the responses were about which Glock I should get instead.

Back o the piston... I too am in the market for a piston AR type rifle. I am completely guilty of being in the "because I want one" category. The only technical reason I can come up with is that it will get me past the "Don't you already have one of those?" argument my wife will make.
 
No problem. I own many rifles I don't need. I have a 50BMG, .338LM..etc. I don't hunt and rarely shoot competitions anymore. I enjoy shooting, not for others but for myself. I own two Piston AR's and will not part with either of them. My first one was because I wanted one, then I started shooting suppressed and really working the rifles hard. They have never had a single issue. And before it is brought up. Don't worry about carrier tilt. I have seen it in a couple piston guns, mainly due to the wrong buffer and spring. I shot an HK MR556 in Georgia that had over 45,000 rounds with no breakage. It still shot 1 1/2- 1-3/4 MOA with factory ammo. They shoot around MOA out the factory door. For a 16.5" rifle it is pretty good. I have quite a few AR15 rifles of various makers. If I want precision, I go with my RRA 24" varmint, if I was run and gun for a course I pick one of my piston rifles. My Sig now has an Aimpoint PRO on it and the Hk is my K.I.S.S. rifle, with nothing but diopters.

If you want a piston gun, get one. PM me when you do. I honestly do think the Sig 516 is the best for the money. The Hk is arguably the best out but is heavy and expensive. LWRC is being bought by Colt, I am impressed with their products. I hope Colt holds just as high of a standard. As far as other piston systems, I have shot Adams and a small company here in NC that makes its own. I decided to stick with Sig and Hk.

Have fun deciding and let me know what you get..

P.S. I have not shot the Colt Piston gun but hear it is pretty good also.
 
I own multiple AR's. All were DI. Since that's what I used in the US Army, that was fine with me. But one day on the Ruger Forums a guy popped up with a lightly used Ruger SR556. The $1500 top of the line model. He had put a few mags through it and decided he wanted to go a different way. So he sold it to me for $995.

I changed the stock, the trigger, the pistol grip, put a Battle Comp on it, etc. I ended up with a rifle that I like a lot more than I really expected to. People like to ask that "if the world was exploding because of XXXXX and you had to fight to stay alive and could only take one rifle, which would you trust?" The Ruger has slowly but surely worked its way into that position for me. It's a sort of middle of the road rifle, not the shortest I own, not the longest. Not the lightest, not the heaviest. Not the absolute most accurate AR I own but not far back either. Has been 100% reliable with all loads I've tried. Some firearms just have "the right feel" to them. In my case, that's true of the Ruger. I like mine a lot. When CDNN was selling the 6.8 version for $999, I should have bought one!

Gregg
 
Joe Mamma said:
Two things:

1)

2) Actually, 100% of the gases (which is used to cycle the gun/bolt) ARE directed into the upper receiver. Some of that gas makes it out the exhaust ports in the carrier. But technically, that gas still went into the upper receiver (which houses the bolt carrier and gas key).
Click to expand...

Never claimed otherwise

This point is significant not so much for the dirt/powder residue issue, but because of the heat issue.

Joe Mamma
Click to expand...

What heat issue? The gases have cooled significantly by the time they get to the BCG. The piston in the carrier doesn't get very warm at all. It's the piston in the gas block that get hot.

I don't care if folks want an upper with the piston in the gas block with an oprod or not. I'm just addressing the misconceptions about both types systems
 
Originally Posted By MistWolf:

Originally Posted By Joe Mamma:

Originally Posted by Joe Mamma View Post
Two things:

1)

2) Actually, 100% of the gases (which is used to cycle the gun/bolt) ARE directed into the upper receiver. Some of that gas makes it out the exhaust ports in the carrier. But technically, that gas still went into the upper receiver (which houses the bolt carrier and gas key).
Never claimed otherwise

Quote:
This point is significant not so much for the dirt/powder residue issue, but because of the heat issue.

Joe Mamma
Click to expand...
What heat issue? The gases have cooled significantly by the time they get to the BCG. The piston in the carrier doesn't get very warm at all. It's the piston in the gas block that get hot.

I don't care if folks want an upper with the piston in the gas block with an oprod or not. I'm just addressing the misconceptions about both types systems
Click to expand...

MistWolf, the first part of what you quoted was in response to what ugaarguy wrote, not you.

You bring up an interesting point about the heat. I actually don't know how much heat is dumped into the receiver area with DI guns. Maybe it's not nearly as much as most people think.

Joe Mamma
 
It is actually quite a bit. I can run a 416 upper for 90 rounds and handle the BCG, I can't do that with a DI gun I have found yet. I will have to wait and see the difference when the Marines use the IAR M27. Until then I would think it isn't a great big difference because the barrel and chamber still heat up the same. The heat wasn't as big of an issue as the fouling put back into the receiver.
 
My Colt running 90 rounds as fast as I can fire will burn me to pull the carrier out. I will try to get it out and use a laser thermometer on both as soon as the weather breaks here.

Note: the Colt will bake off round somewhere over 300. I ran it on a buddies demo lower and it surprised me how hot the whole gun got. It was hot enough to burn flesh, and uncomfortable on my hands with the handguard getting hot on top.
 
The barrel & gas block get plenty hot. The Magpul MOE handguards do a good job protecting the shooter's hands. When I pulled the carrier out, the gas key was a uncomfortably hot but it cooled rapidly.

Another guy ran a test on the two types of uppers using a laser thermometer and he found the oprod upper to be about 40 degrees cooler
 
My Colt running 90 rounds as fast as I can fire will burn me to pull the carrier out. I will try to get it out and use a laser thermometer on both as soon as the weather breaks here.
Click to expand...

Did you leave the carrier locked back between reloads and after the last round? Are you running carbine-length gas or rifle-length? Remember that contact with a hot barrel extension will heat the bolt and carrier too.

I've shot my 16" RRA midlength in carbine matches and have never noticed the bolt carrier being anything above warm. Of course, the further the gas is from the carrier, the cooler it will be (passing through the skinny aluminum gas tube cools the gas quite a bit).
 
Of course, the further the gas is from the carrier, the cooler it will be (passing through the skinny aluminum gas tube cools the gas quite a bit)
Click to expand...

I'd bet against this, on such a short time scale the adiabatic assumption is generally pretty good, meaning external cooling is negligible. But the expansion of the gas in the tube and bolt carrier will cool it, although the longer tube lets it expand (cool) a bit more. But even if the gas is cooled by a factor of 10 its still hot!

I've never had the DI bolt carrier getting hot enough to be an issue, but getting crudded up is another story.
 
Actually, there is cooling of the gases as they pass through the tube. The gases are losing pressure as they fill the volume of the tube. A drop in pressure throws off heat. The gas tube absorbs this heat and transfers it to the air. With a heavy firing schedule, the tube will glow red at the gas block and will finally fail at that point.

The gases also cool after passing through the gas port. Most gas blocks have a small chamber between the gas port and the gas tube. When the heated gases pass through the small port and into the chamber in the gas port, pressure drops and the gases dump heat. That's why gas blocks get so hot. Gases also dump heat after exiting the gas tube, whether it's into the expansion chamber of the BCG or into the open space in the upper after the gas key separates from the gas tube. By that time, there's not much heat or pressure left, giving only a soft puff of air out the carrier vents
 
My point is any cooling dominated by the gas expansion, not transferring heat to the air around the gas tube, the fact that the tube remains filled with atmospheric pressure very hot gas (despite its "cooling") between shots explains why the thing will eventually heat up enough to fail if you run it hard enough!
 
Ben, I am running carbine length gas systems on all but my RRA. The bolt is locked but I do a quick mag change and fire as fast as I can. I was testing to see the difference. The Hk was quite a bit cooler than the Sig 516, but I have a feeling it is due to the self regulating gas block. It releases a LOT of gas out the gas block. The Sig doesn't seem to bleed as much pressure. The Colt after shooting 200-300 starts cooking the CLP off of the bolt. I swear I am beginning to think something is wrong after talking to you guys. The Colt has to be dripping with oil to run it like this.
 
Small Arms Review conducted a torture test a couple years ago. They took a POF piston gun and a "DI" gun and ran them full-auto using Beta C mags. Temps were taken at certain points along both uppers after each mag dump.

The idea was to get ten mags through each platform but the DI rifle suffered a ruptured gas tube after something like three mags.

I don't have the article in front of me so forgive me if my memory is wrong. I seem to recall the POF reached 400 degrees at the gas block while the bolt and carrier hit something like 200 degrees.
 
Originally Posted By USBP379
The idea was to get ten mags through each platform but the DI rifle suffered a ruptured gas tube after something like three mags.
Click to expand...

Yeah, I've heard of gas tubes melting in extended rapid fire situations like that.

Joe Mamma
 
Small Arms Review conducted a torture test a couple years ago. They took a POF piston gun and a "DI" gun and ran them full-auto using Beta C mags. Temps were taken at certain points along both uppers after each mag dump.

The idea was to get ten mags through each platform but the DI rifle suffered a ruptured gas tube after something like three mags.
Click to expand...
I'm not surprised. The M16 is an assault rifle. It's not a light machine gun. If you treat an op rod piston AR like that you'll burn the bbl out in short order. If you actually NEED to run that many rounds full auto you need a true machine gun, like an M249 SAW at minimum. That torture test is completely unrealistic.
 
ugaarguy said:
........torture test is completely unrealistic.
Click to expand...

Not necessarily. The whole idea of the external piston is to provide users who fire a whole lot of rounds in a short time with a platform that better deals with the stress and heat that will ruin a gas tube. This is why some who need the capacity of sustained automatic fire are switching to systems like the HK.
 
wally said:
My point is any cooling dominated by the gas expansion, not transferring heat to the air around the gas tube, the fact that the tube remains filled with atmospheric pressure very hot gas (despite its "cooling") between shots explains why the thing will eventually heat up enough to fail if you run it hard enough!
Click to expand...

The fact the tube gets hot means it's taking heat from something and radiating it to the air. That means that whatever is heating the tube is shedding heat. If the gas tube were not transferring heat and radiating it, it would be cool to the touch

USBP379 said:
Not necessarily. The whole idea of the external piston is to provide users who fire a whole lot of rounds in a short time with a platform that better deals with the stress and heat that will ruin a gas tube. This is why some who need the capacity of sustained automatic fire are switching to systems like the HK.
Click to expand...

The problem with this theory is the fact the HK uses a heavier profile barrel than the M4. The barrel is the major heat sink. The M4A1 uses a heavier profile barrel which significantly increased the heat (increasing number of shots fired) before the gas tube failed. Perhaps the piston in gas block design of the HK does handle the heat better than the gas tube, but in this case, because HK uses a heavier profile barrel, it's not a direct comparison
 
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