A R Rifles Gas or Piston?

[Tronster]

Its not about refusing to clean a gun, a GP just means I get to spend alot less time cleaning and more time doing other things. I find that if a gun is a PITA to clean then I rarely shoot it.

[FJ540]

Took about 1K rounds of wolf before mine was gunked up enough to need cleaning. I won't do piston. There's nothing that can justify a reciprocating mass on a barrel for me - it's inherently inaccurate.

[Tronster]

If you like your DI gun then that's all that matters for you, but don't be too quick to dismiss some of the advantages a GP offers.

The Huldra guys have a series of vids on youtube where they tested a Huldra chambered in 5.45 and used corrosive Russian surplus ammo (5.45 is cheaper than 5.56). They ran it with no lube and no cleanings over several months. It wasn't til about 4500 rounds they had their first malfunction (failure to feed) and then a handful of dud primers with the surplus ammo. This is with NO lube and NO cleaning.

The last two vids:
http://www.youtube.com/watch?v=0h6cSAnlzlE about 4000 rounds
http://www.youtube.com/watch?v=DUcpiVNfHZM end of test

But I think the key to keeping a DI gun running when really dirty is lots of lube.
As far as accuracy a GP may open the groups up a little bit, but not horribly like a Ruger Mini 14. That thing I'd be lucky to hit a cd twice when the barrel is hot.

[FJ540]

I'm firmly planted in the "GP is a solution looking for a problem" camp. It's not from lack of understanding of the reasons for it, it's from understanding the reasons against it.

[NMRMN]

I'm firmly planted in the "GP is a solution looking for a problem" camp. It's not from lack of understanding of the reasons for it, it's from understanding the reasons against it.

What reasons? I understand the system is more complex, but apparently more reliable. Accuracy? Seems they accurate 'enough'...

[FJ540]

If a gun won't shoot 1 MOA, I sell it.

[Holland&Holland]

If a gun won't shoot 1 MOA, I sell it.

Remind me not to buy a gun from you...

[Tronster]

Instead of a gas tube it has a fixed piston in the gas block, a solid one piece op rod that fits over the piston, and a return spring for the op rod. That's it, a very simple design.
The only failures I could see happening is someone being stupid and bending the op rod, or the return spring weakening. If I'm that worried about the spring I'll just replace it periodically like a recoil spring of a handgun.

As far as accuracy, I'm not competing with it or shooting the bullseye out. I'm smackin' steel plates at 2-300 yards with irons and doing rapid shooting drills. Shoots a hellavalot better than the mini 14 did and that suits me just fine.

[FJ540]

If a gun won't shoot 1 MOA, I sell it.

Remind me not to buy a gun from you...

That's not the only reason I sell them. Usually it's from lack of interest in it for whatever reason, but there have been a couple in the past that I couldn't make happy with factory ammo and they weren't welcome in the collection because of it (before I got into reloading).

The piston is the problem Tronster - that's what makes them inherently flawed. You can't have a "bouncing baby" on your barrel and eliminate harmonic interference. It's a flawed design. There is no fixing it. The piston wiggles and adds shock to the barrel before the bullet escapes the bore.

[Tronster]

And I got a GP gun knowing full well it won't be a 1 moa gun. I understand the piston influences the barrel somewhat, but for ME it's not a deal breaker. I mentioned earlier that if you want absolute accuracy then DI is the way to go. I work with a guy who is all about sub-moa, and handloads for ultimate accuracy and would not be happy with anything but sub-moa. PERSONALLY I'm ok sacrificing a little accuracy for ease of maintenance, so a 2 moa instead of 1 moa is fine by me and my type of shooting. I'm just giving the OP a full account of my experience with GP and my reasons for choosing it, and you can state your reasons for staying with DI.

[NMRMN]

FJ540 -- you ever shot a HK MR556? Those are supposed to be pretty accurate...

[FJ540]

Nope. And not all piston guns are inaccurate - but the AR piston systems have different accuracy claims from people like JP and Les Baer - why would they do that if not for knowing about the problem?

ETA: 3 shot groups "some" being sub MOA? 5 shot's minimum, and it should be all day long.

"Definatelty got some sub-moa groups with three shots groups with the 69gr"

http://www.hkpro.com/forum/hk416-hk417- ... eport.html

[Tronster]

To the OP keep in mind only the lower is serial numbered, so if you get a quality milspec lower then you can add either a DI or GP upper to it. You wont be stuck with one or the other permanently. I cant speak for price since AR prices have been typically 50 percent higher since December.

[Chevydude]

That's some good stuff Guys. What else can I learn from ya? When I go shopping I like to know what I want.
I'm pretty green when it comes to AR's. Thanks everybody.

[Tronster]

I'll tell you what I personally look for:

I want the upper and lower receivers to be forged 7075 T6 aluminum with hard anodizing. Some receivers are billet, but most are forged and people seem to prefer forged. There are polymer lower receivers out there but I would recommend sticking with an aluminum receiver.

The rear buffer tube will be either commercial or milspec type, and it will make a difference if you order a different buttstock later as you need to specify commercial or milspec. I think the buffer tubes are also different for fixed and collapsible buttstocks, so if you want to switch buttstock types you may need a new buffer tube.

I just use a standard AR trigger which is ok but there are target triggers available and often in lighter pull weights.

A barrel and chamber that is either chrome lined or melonited. It helps prevent cases from sticking in the chamber and provides corrosion resistance in the bore. There is a TON of science and discussion about one or the other and which is better, more than I can get into here.

Recommend a flat top upper receiver with a rail. You can add a detachable carry handle, iron sights, red dot sight, scope, night vision optics, or any combination of those. A fixed carry handle upper really limits what you can attach for optics.

The front gas block (FGB) can be either an integrated fixed sight or a flat top rail for a detachable front sight. Just don't put a polymer sight on the FGB, it gets VERY hot. There are standard and 'F' marked fixed front sights, which are very slightly different in height. Not sure what each are meant for (ie for fixed carry handle, flat top upper, etc) so you'll have to read up on that. I just have a railed FGB.

Front hand guards can be a standard round A2 or a modular polymer like magpul or a freefloat rail system with rails and covers 360 around. Your preference on that, some can be changed for others.

As discussed before, there is the direct impingement and the various gas piston systems. DI has been around a long time and the gas tube parts are mostly standardized between manufacturers. There are all sorts of GP systems and designs and each type is proprietary. The Adams Arms seem to be a popular alternative to the more expensive high end piston systems and some manufacturers use them in their factory builds.

DI is a reliable system that's been around a long time and works and has minimal detriment to accuracy. It's simple and with regular cleaning and liberal use of lubrication when dirty it will run a long time. It does blow alot of carbon and heat into the upper receiver and can cook off lubrication essential to smooth function so be sure to keep the bolt well lubed.

GP is relatively new and each design is different. It will add some weight to the rifle and extra moving parts to the operating system, and the piston drive can effect accuracy somewhat because of it's contact with the FGB. However, it keeps the hot gasses and carbon out of the upper receiver and greatly simplifies cleaning, and does not affect the lubrication of the bolt carrier. It's especially useful in short carbines or when suppressed.

As for the bolt carrier group (BCG) look for one that is a full auto vs semi auto design. You can see the rear of the bolt (top left of stolen picture) will have uneven top and bottom halves on the semi auto, where the full auto (M16) will be even top and bottom. You also want a fully shrouded firing pin. In the center picture the top bolt has an exposed firing pin while the other two fully shroud the pin. This protects the firing pin from the hammer when the bolt cycles. You want a properly staked gas key (google it for examples), and if possible the BCG is high pressure tested (HPT) and magnetically particle inspected (MPI). If I think of anything else I'll post it up.