AR piston versus DI - an honest debate

[Warp]

That lack of standardized parts thing is enough, by itself, to keep me, personally, from having any interest whatsoever in a piston AR.

The DI AR, among all of its other awesome attributes that have led to it being so incredibly popular, is extremely standardized in terms of parts fitting and availability. Not all parts are created equal and we all have preferences, but even outside of those preferences there are a <deleted> ton of other parts that will fit just as well, and function as designed, and there will be for a long, LONG time. Those parts, and other rifles that can be used for parts, are absolutely everywhere.

 

[Ohen Cepel]

I carried a DI rifle for about 25 years, some of those in the sand. I don't own a piston rifle since I just don't see a reason for it in my world.

Local smith who I respect will no longer work on AR piston rifles since he just is never able to get them to the level that he wants his work to be at.

If you built it from the ground up a piston makes sense and I'm not opposed to piston guns. However, putting it into an existing platform like the Stoner design comes with it's own issues (bolt tilt for instance) which I just don't think is the way to go.

 

[HKGuns]

I own both which is the correct answer. There can be little to no argument that a piston rifle stays a LOT cleaner In the bolt area. Anyone who argues otherwise has never owned a piston.

 

[mljdeckard]

It may be somewhat cleaner, but the question isn't whether it's cleaner. It's whether the added fouling increases the chances of a malfunction.

One afternoon I cranked through 500 nearly straight rounds in a Bushmaster M-4gery, using Wolf ammo. Entry-level rifle, rock-bottom ammo, zero malfunctions. I think I put some lube on the BC halfway through.

 

[Zoogster]

I would say that DI is more reliable in a clean rifle. It is simplier with fewer moving parts. This means less to go wrong.
So I would say it is better for most civilian use, less to go wrong.
But depositing residue in the action after every shot does mean the action will get dirtier sooner, which eventually can start causing problems.
So should be more reliable mechanically to start, and be gradually decreasing as you get further from a cleaning.
The round count between cleanings for most civilian uses is not that high, so increased reliability and simplified design with DI makes more sense.

On the other hand if you are laying down suppressive fire and burning through large numbers of rounds then the residue from each round is going to add up quicker in the action. At that point it may be beneficial to go with a piston. This residue will build up even faster if using a suppressor, which the mentioned SOCOM operators often will be.


So DI should be more reliable and a better option for most, but it really depends on your intended use. I would rather have DI for most uses.
It is hard to mess up a tube that goes to the action. You get it the right length, the right diameter, and it will consistantly provide the same amount of gas with the same loads. A piston on the other hand is something that wears and changes over time because it has moving parts.

 

[Warp]

If you start with a properly lubed DI gun, you aren't going to be able to carry enough ammo to get it to the point where there is any concern. And if you do carry that much, or get a resupply in the middle of your battle, throwing some lube onto the bolt through the ejection port (which you can store in a grip core or stock compartment, or with your resupply of ammo) will be more than adequate to get your into the many hundreds of rounds.

I have fired my DI gun for ~450 rounds in an afternoon and it was probably good to go another 450, had I asked it to, at which point I would have added some lube.

 

[Ridgerunner665]

I have both...but I like the piston better (Sig 516 gen 1)...the design is just as simple and reliable as the DI.

Is one any better than the other...no...both will do the job just fine.

This kinda reminds of when Glock pistols first came out...

 

[boricua9mm]

I own both which is the correct answer. There can be little to no argument that a piston rifle stays a LOT cleaner In the bolt area. Anyone who argues otherwise has never owned a piston.

The DI system is self-limiting in the amount of carbon buildup. The bolt of a piston gun may seem cleaner on the tail, but they are taking a big dump in the gas block, which if neglected, can cause some serious problems.

Guns get dirty, period. So long as firearms continue to use gunpowder it is something that has to be dealt with one way or the other; having a piston doesn't eliminate the need to clean.

A bolt being dirty doesn't automatically make a gun unreliable. If that were the case, the roller-locked HK pattern rifles would have been nothing more than prototypes. In fact, by comparison it's almost comical that anyone would complain about cleaning an AR15. Doesn't matter much though; the gun is designed to manage the grime. Same thing goes with a DI AR15.

I ran my BCM upper for 1,000 rounds without cleaning. It was lubed with Mobil 1. The gun never missed a beat and it never even slowed down. It began to stink really bad, so I cleaned it. A little carbon buildup on the tail of the bolt was inconsequential. In the rest of the BCG, the carbon was simply captures and carried away in the lube.

 

[mljdeckard]

I know one competition shooter who has shot at least 5,000 rounds through the rifle he uses for three-gun. Never cleaned. Lubed heavily.

 

[HKGuns]

A bolt being dirty doesn't automatically make a gun unreliable. If that were the case, the roller-locked HK pattern rifles would have been nothing more than prototypes. In fact, by comparison it's almost comical that anyone would complain about cleaning an AR15. Doesn't matter much though; the gun is designed to manage the grime. Same thing goes with a DI AR15.

If you read my post carefully you will not see reliability mentioned. The bolt area is far cleaner and thus less of a hassle to clean, which is of value to me. The piston on my piston rifle stays very clean also.....there just isn't a ton of crap floating around anywhere in my piston rifle, some very minor carbon buildup on the piston itself that cleans up very easily.

I will hazard a guess that the gas port is smaller to pop that little piston in the front of the gun as compared to the amount of gas required to fill the gas tube and cycle the bolt directly. Less gas running around inside the rifle should equate to more crap out the end of the barrel. i don't have enough technical knowledge to say for certain that this is the case. Cleaning the gas tube is a pain in the rear too, now that I think about it more. Advantage piston if for nothing more than ease of cleaning.

Higher grade Italian shotguns ave been running pistons for years. The main innovation / advancement you see from generation to generation is primarily in ease of cleaning. My Beretta 391 Urika, gas operated, 12ga is a pain in the rear to clean when compared to my 391 Xtrema2. This stuff matters to folks and people who make a shotgun purchase usually always factor in how easy they are to clean. It takes me over an hour to clean my 391 Urika........I can get my Xtrema2 just as clean in under 15 minutes. Interesting side note is that for its generation the Urika was widely considered one of the easier auto-loaders to clean when compared to more traditional US brands like Remington and Winchester.

So what does this mean? Technical superiority isn't the only area where innovation or advancement in a design matters, there are other factors that can come into play depending on the individual or mission.

 

[Dr.Rob]

DI and a suppressor leads to one seriously filthy rifle.

http://www.thehighroad.org/showthread.php?t=580855&highlight=thunderbeast

I can appreciate if you are shooting a lot of rounds suppressed, moving to a purpose built piston gun (not an after market kit) with a competent armorer (ala spec ops types) might make sense.

 

[kwguy]

If you start with a properly lubed DI gun, you aren't going to be able to carry enough ammo to get it to the point where there is any concern. And if you do carry that much, or get a resupply in the middle of your battle, throwing some lube onto the bolt through the ejection port (which you can store in a grip core or stock compartment, or with your resupply of ammo) will be more than adequate to get your into the many hundreds of rounds.

Very well put. Keep it wet, and it'll run and run and run....

 

[justice06rr]

I hate these debates, but I'll throw in my 2cents anyway.

A true "Milspec" AR15 like a Colt/BCM/LMT/DD etc will run fine with a DI system as long as it is properly lubed and maintained, and using good ammo.

A piston system is nice, but again used for specific purposes. In a good AR like the HK416 or LWRC M6 it will run just as good as a Milspec AR, if not better.

I would happily choose a top-tier DI (Colt/LMT/BCM/DD/KAC) over a Piston, although in other rifles I do like the piston systems i.e. SCAR, AK, etc but those are non-AR platforms. Here is a LMT DI rifle that had around 10k rounds with no cleaning:

http://www.m4carbine.net/showthread.php?t=100162&highlight=lmt+fun



That should tell you something regarding DI AR15 reliability...

 

[boricua9mm]

If you read my post carefully you will not see reliability mentioned.

Understood, I was making the comment for the casual observer. The problem is, people autiomatically equate "cleaner" with "more reliable" and many firearm designs have proven to us that this isn't the case.

Higher grade Italian shotguns ave been running pistons for years. The main innovation / advancement you see from generation to generation is primarily in ease of cleaning. My Beretta 391 Urika, gas operated, 12ga is a pain in the rear to clean when compared to my 391 Xtrema2. This stuff matters to folks and people who make a shotgun purchase usually always factor in how easy they are to clean. It takes me over an hour to clean my 391 Urika........I can get my Xtrema2 just as clean in under 15 minutes. Interesting side note is that for its generation the Urika was widely considered one of the easier auto-loaders to clean when compared to more traditional US brands like Remington and Winchester.

In the case of shotguns, a gas piston system really does offer advantages over something like the Benelli inertia design. The gas guns are more forgiving of various loads, whereas the Inertia-Driven system, while very reliable, has tradeoffs. If we want a Benelli to run really light loads, we make concessions which allow the shotgun to really abuse us when using heavier loads. If we weigh down the Benelli Inertia guns with accessories, then recoil is lessened and reliability is compromised. The gas operated shotguns do get pretty dirty, whereas I've run my Benelli M1S90 for a few hundred rounds only to find very minimal residue of any sort.

I can appreciate "ease of cleaning" as a desirable feature, but having cleaned my old HK93 and MP5 more times than I've cared to, I simply think that cleaning a DI AR15 really isn't a big deal at all, Drill Instructors be damned.

 

[JustinJ]

"DI runs great if it's properly lubed". Awesome. One itty bitty problem. It also tends to burn off lube at a relatively high rate (worse the shorter the barrel) compared to piston operated guns. Does this really matter if one only pops off a few hundred rounds at the local range? Of course not. On the other hand, if one is posted at a FOB on an Afghan mountain, miles from support, and has to repel a protracted attempt to over run the base, stopping to lube just might pose a problem.

 

[Warp]

"DI runs great if it's properly lubed". Awesome. One itty bitty problem. It also tends to burn off lube at a relatively high rate (worse the shorter the barrel) compared to piston operated guns. Does this really matter if one only pops off a few hundred rounds at the local range? Of course not. On the other hand, if one is posted at a FOB on an Afghan mountain, miles from support, and has to repel a protracted attempt to over run the base, stopping to lube just might pose a problem.

You can go WAAAAY beyond a few hundred rounds without having to relube.

Assuming you begin with it properly and sufficiently lubed, of course.

Have you read through this thread?

 

[JustinJ]

You can go WAAAAY beyond a few hundred rounds without having to relube.

Assuming you begin with it properly and sufficiently lubed, of course.

What is "WAAAAY" beyond? What barrel length? What rate of fire? The question is not if one rifle "can" do something. The question is if what percent of a sample size will experience what rate of failures at what round count. The more important question, what rifles will experience fewer.

I agree, a soldier on patrol 'probably' won't carry enough ammo to make lube burn off an issue but that is not the situation I cited.

 

[MistWolf]

A short barrel is not harder on lube than a longer barrel. What may make a difference is gas system length.

It's strange that folks talk about piston systems being better while ignoring the fact the AR already has a piston

 

[back40]

justinj, currently my 6920 has gone well over 1k(probably approaching 2k) without being cleaned or lubed. 16 bbl, carbine gas. only mods other than sights have been a centurion c4 12 fsp rail. rate of fire has been slow fire match ammo fired from a bench to accuracy test, mags dumps at 50yds by new shooters (i don't get into mag dumps, but the smile from new shooters doing it is worth it), and everything in between. it's a sample of one, sure, but i doubt i'm so lucky to have the only ar capable of such performance.

i have nothing against piston guns, but the lack of standardized parts and support kills it in my mind. i don't have any safe queens and how clean a rifle stays isn't much concern to me.

 

[Warp]

What is "WAAAAY" beyond? What barrel length? What rate of fire? The question is not if one rifle "can" do something. The question is if what percent of a sample size will experience what rate of failures at what round count. The more important question, what rifles will experience fewer.

I agree, a soldier on patrol 'probably' won't carry enough ammo to make lube burn off an issue but that is not the situation I cited.

I don't suppose you have answers to your questions? Citable, statistical, matter-of-fact answers? Because observations of many MANY people, in many MANY situations, say it isn't a problem.


This situation?

"DI runs great if it's properly lubed". Awesome. One itty bitty problem. It also tends to burn off lube at a relatively high rate (worse the shorter the barrel) compared to piston operated guns. Does this really matter if one only pops off a few hundred rounds at the local range? Of course not. On the other hand, if one is posted at a FOB on an Afghan mountain, miles from support, and has to repel a protracted attempt to over run the base, stopping to lube just might pose a problem.

I somehow think that situation isn't relevant to the topic of this thread to begin with...but let's pretend that it is relevant, for some reason...

How many rounds would a rifle that begins the protracted battle properly lubed be able to reliably fire?

 

[cougar1717]

Any "which is better?" discussion is tough because both have detriments. I hate to say this, but the game changer would be if the armed services bought piston rifles, even for limited uses. Then, there would at least be a standard for interchangeable parts. Proprietary systems are great and innovative, but unfortunately DI has a leg up due to common specs.

 

[breakingcontact]

Very interesting how there are now AR15 purists. Same type of people who resisted the AR15 in the first place I'm sure. Times change folks, things improve. If you don't consider it an improvement, great, but don't hate it. I like AR15s but still like M1As. A piston AR15 that proves reliable, to me, is a better gun than a DI gun, but a DI gun is not a bad gun.

 

[back40]

i'm certainly not an ar purist, but breaking contact, care to explain better how? the already stated concerns with standardization and support put piston guns at a huge disadvantage.

 

[breakingcontact]

Surprised you guys aren't holding onto the M16A2 still! It's fine man, if you like your DI gun, cool, great, there are advantages but there are disadvantages too. The whole "nothing is standard" argument can be overcome as well. If you have a piston guy, buy the parts BEFORE you need them. I do that with all of my guns, maybe y'all don't? AR15 parts (DI) are everywhere right? Well, they weren't for a long time this year, but I had already bought extra parts.

So to me, the whole lack of standardization/lack of parts thing isn't an issue, but I get that it is, if you are the sort that isn't prepared, with stock on hand, to fix your own guns.

 

[Warp]

i'm certainly not an ar purist, but breaking contact, care to explain better how? the already stated concerns with standardization and support put piston guns at a huge disadvantage.

I am also interested in this ^