Thinking about doing a gas piston ar build, I just want to know how much more reliable these kits are than di. Also which kit is the best and works with the widest variety of rails

Depends on same variables that apply when purchasing a DI upper. Manufacturer, design, parts commonality, compatibility with DI parts, extra "whiz-bang" features, etc.

I have a had a good experience with the Sig 516. I also have a lot of respect for certain PWS and Syrac Ordinance designs.

Ive never seen a normal ar jam up and thought "man, an op rod would solve that problem"

A normal ar already has a piston, its part of the bcg

you will see no increase in reliability

I have DI and piston drop ins I use the OPS416 from osprey ive had it 5 years over 10k rounds on the system no problems or carrier tilt..I use socom barrels 14.5/phantom 5C1 and H3 buffers runs like a sewing machine.

Dude, ARs shit where they eat!

 
This. And adding parts to increase reliability is counter-intuitive.

I would never buy a piston kit... however a 6.8mm from LWRCI is on my wish list....

I have an add-on Adams kit on one upper and a factory Adams (Huldra-branded) upper, and my only Sig (so far) is a piston-operated 716 Patrol rifle in 308.  All are rock solid performers.  I've never had a stoppage due to gas system on any of my ARs, both "traditional" and piston.

I think it's interesting that a piston upper "feels different" from a traditional gas-tube type upper when fired.  I can't describe it, but it's different.

Except that you aren't. Piston ARs have fewer parts than DI...

DI parts list:
Gas block
Gas tube
Gas tube retainer pin
Gas key
Gas key retainer screws (x2)
Bolt gas seal rings (x3)
DI bolt carrier body
Total parts: 10

Piston parts list (Adams Arms)
Gas block
Piston seat
Piston/op rod
Piston bushing (seats on barrel nut)
Piston return spring (optional for function)
Piston bushing (installed in upper)
Bolt spring
Piston bolt carrier (one piece design)
Total parts:8 (7 if you omit the optional piston return spring)

And here we go...  The Big M4 Myth

Also keep in mind that all piston systems are proprietary.  Sig's is different from HK's which is different from LWRC's, and so on.  Whereas I can go to any gun shop and buy a DI gas block or gas tube for cheap and it will work.

How clever.

I will reword that for all to make sense, and it fits the OP

Replacing the entire reliable, and proven operating system to increase reliability is counter-intuitive.

Especially since most if not all piston systems are proprietary, and parts will no longer interchange with my 10 other rifles (or the 50 others of people I know)  It just does not make a reliable change for me, or mine.

I have a 5.45x39 Adams Arms piston upper that I run suppressed at least 50% of the time.  It sure makes a huge improvement with dirty Russian ammo and not having all the gas blow back in your face.  My other AR's are DI and are going to stay that way.  Piston serves me well for the niche it fills for me but I see no reason not to stick with DI for the others.

Topic Moved

Nobody's denying that DI rifles can go 1000+ rounds trouble-free without any cleaning or lube. But it's also a fact that piston systems build up fouling in the action at a much slower rate than DI guns, and the lube you put on the action parts will stay where you put it much longer with a piston mechanism vs DI.

Stated another way: do you have any proof that piston guns are LESS reliable than DI guns when set up properly?

I have both DI rifles and a AA piston kit rifle.  I can tell no difference between them as far as reliability goes. They both run without issues through 1000+ rounds between cleanings.

While true that adding parts may complicate things, it is a blanket statement, some items are improved with an additional part or two. I can add 4 tire chains to my car, 4 more parts, but then I can drive on a snow covered road that would stop my car otherwise.

I have an Adams Arms piston, just because. The extra parts it adds to the system is negligible, in my view, because they are all fairly large, robust parts. You are removing some items too, like the the gas rings on the bolt. I can not say that I have tested either system to failure. It feels like the recoil impulse is a bit stronger with my piston kit, but the trigger action is dramatically cleaner, and that, in my view, will probably help reliability in some environments. Probably the DI system is a bit more accurate, since there are less mechanical interactions going on, but the difference is probably negligible out to 200 or 300 yards.

 
Can you please explain how your trigger action is cleaner because of what happens to the gun after the hammer has fallen?






Aside from your -in my opinion- nasty recoil impulse, what will your Adams Arms gun do that mine won't?



I've had one, and still got gas in my face when shooting suppressed. Can't say for reliability due to dirt, Ive never had my RR M16 stop due to being dirty from it's own shit. And I clean that thing about once a year, if I remember it.






And then let's not talk about carrier tilt, which requires more additional gadgetry to get under control.






Anyway, I'm happy you like your Pistons, I've tried it and am not a fan.



I feel it's the answer to a question no one asked.




 

With all respect I have to completely disagree.  The piston imparts mechanical forces the DI system cannot, while running cleaner (more reliability right there) and cooler.  I've had well groomed DI ARs fail plenty of times with no such problem with pistons.  Die hard DI guys are die hard DI guys but the superiority of a piston mechanism isn't even a logical argument, it just is.

 

A piston system, like the Adams, doesn't deposit ANY of the typical soot and gunk in the lower the way a standard AR does.  The lower receiver, and importantly the FIRE CONTROL GROUP stay much cleaner.  With appropriate tweaking to the carrier (done by Adams, not the rifle's owner), carrier tilt is negligible at most.

Can't say I've had any function issues with my LWRC. Last time at the range I ran 420 rounds consecutively through it and had no malfunctions of any kind. I was doing this at a rate that would jam up much DI systems as I have done so with my issued m4 and had it jam on me multiple times when we were blowing off excess ammo at the range.

I can't talk to every piston kit out there but I have more ARs than I can reasonably shoot, only one is still DI. Everything else is now running an Adams Arms piston kit.


I've had no reliability issues with them and the firearms run much cleaner with less gassing, debris etc.. They are generally much cleaner to shoot. I'm probably going to keep the remaining DI gun as a DI but not because it is much better, simply because it's nice to have one and be able to refer to it when folks give me crap about running Pistons.




Piston guns are certainly no less reliable or accurate than DI guns and they do have some advantages, mainly around lowered reciever heat and fouling. I do belive DI guns can be a little quieter when shooting  as the recoil gas is vented inside the reciever rather than out of a gas port/piston tube etc but the difference is marginal.




As to the specific question of reliability, I've not had any of mine fail me, yet. I have had the DI gun require new gas rings, fail due to excessive fouling and once a busted bolt. This was I believe due to heat damage. The same has so far never happened in a piston gun.


 

I went with the LMT MRp upper with a piston so that when I get my period every month I can just switch the barrel back to DI for a week.

I would say after all the YEARS of these arguments there are plenty of 100% reliable options in either flavor OP. do you're research and go with what you want.

Most DI guns will stop running after 1000-2000 rounds without cleaning or lubrication. A friend of mine used to run a range, and had an Adams Arms piston rental gun that went through over 7500 rounds without any cleaning, lubrication, or malfunctions.

They are reliable if they are high quality.  Remember, piston is not a win-all system, it's just a win most.  You need to determine what your needs are.

Typical reasons people choose pistons:
1. Cleaner where it counts.  (DI guns dump enormous amounts of hot gas onto the extractor and BCG. Carbon buildup is the typical risk. Piston aids in reducing failure to extract due to contamination.  Will not aid in FTE due to other reasons, such as out of spec cases, worn extractor, etc. Either way, heat can carbon on the BCG is never better.)
2. Easier to clean.  Pulling out piston from the front of the rifle, wiping of the piston, and re-inserting.  Don't even have to take out receiver pins, etc.  BCG cleaning intervals significantly longer with piston.  Even this alone makes life wonderful.

Typical reasons to stick with DI:
1.  Extremely common, inexpensive by comparison.
2.  Typically a bit lighter, but relevant for those doing ultra-light builds.
3. Our military uses primarily DI, so there is some association inclination.  Both systems are combat proven by various international militaries.

Don't buy it for general reliability unless you plan to shoot more than 5000 rounds between cleanings, which would be very unusual for a civilian.  Both systems will suffer from the same external influences, such as ammo, condition of components, environmental conditions, etc.

However, buying it to make the maintenance of the firearm simpler is well worth it, and at least has been for me and others I know.  To restate that in other words, you can get increased reliability if your firearm is poorly maintained (which can happen when you're in the field, but typically not in the suburbs).

I converted my DPMS with the Adams Arms kit if anyone cares.  0 failures in either the piston or the DI configuration to date.  But I take care of my stuff.

How about an answer that actually addresses the OP's original question... eh?

Reliability... there is nothing definitive here.  Common sense tells you that clean is better than dirty for anything mechanical, and that heat is also bad on anything mechanical.  However, the DI system has proven to be exceedingly reliable and there is no denying that.  I believe this shows that the system is overbuilt, much like an old Rolls Royce; smaller, lesser components could be made to function (see Kel-tec PLR-16), but without the market drive for one nothing has been designed as a replacement.  

Contrary to all this, however, is physics is still physics.  Heating/cooling cycles fatigue metal, and lack of lubrication for extended periods causes components to wear faster.  I'm thinking that anyone here with an IQ higher than their shoe size will agree to both points.  The DI system gets hot, especially in combat-type situations where it matters most.  In addition to this the quality of the ammunition has a varying effect based on how clean the powder burns.  Put dirty ammo into a fatigued gun and I can presume, without much reservation, that the components will fail faster.  How much faster is a manufacturer to manufacturer data point.  The typical failure point is lugs on the bolt.  As the bolt is subject to both the heat cycling and the lubrication issues it would make sense that it would fail faster in a DI gun.  Will you ever get it to failure?  Doubtful in the hands of the average citizen, and will likely serve you forever without braking anything.  The reason that no one here can say difinitively that one will outlast the other is because only one of the 2 has ever been in a theater of combat (sort of).

Conversely though the external piston systems have the potential to outlast their DI counterparts, because there are no heating cycles placed on the components that matter the most to function.  Do a mag dump on a full-auto piston gun and the bolt heats slightly and the carrier not at all.  The gas block and piston will get exceedingly hot, but gas blocks always do no matter the system.  I would also say that the material making up a drive rod for a piston system is far more durable than that of a gas tube, and therefore far less likely to suffer ill effects associated with the heat as it is immediately evacuated from the system by either offgasing immediately, or returning through the gas block to exit the barrel, both of which seem far more conducive to reliable function to me, keeping the heat and the unburnt materials that can cause fouling outside the operational system.

Here's what the DI guys hate to admit, hot is still hot.  I prefer my hot somewhere else. Let's assume for a moment that in the heat of battle you break your bolt.  With a piston gun you remove the bcg, replace the bolt, get back in the fight.  With a DI gun you open the gun, find a pair of welding gloves or something else you can grab a 600 deg chunk of steel with, then try to cool it down enough to get the bcg apart, new bolt in, and back into the fight.  The DI gun consumes its lubrication in heating, the piston gun never heats up so no loss of lube (which is why I get to run grease here).

As for best system Adams is probably the industry standard for aftermarket systems.  I have one on every AR I own, and they have yet to fail due to their own fault.  I will say, to full disclosure, you have to get them installed CORRECTLY, as I had a drive rod bend on me due to failure to completely clearance a drive-rod bushing at a FFHG proprietary barrel nut.  Once this was found and corrected and the rod replaced (by AA on their dime, even though I freely admitted I screwed up) I have run thousands of trouble-free rounds.  "best" though, for me, include the customer service, and they have helped me figure out issues that had nothing to do with them (port distance on a pistol barrel was too short, but they measured theirs for me to compare) and have been more than willing to help, even when they had no responsibility to.  Cody and Aro over there could not be nicer, and based on customer service alone they would be hard to match.

The AA XLP system will give you the ability to clear a lot of FFHGs.  The last few rifles I've built have been with the XLP and the Midwest Industries SS Gen II FFHGs, and the only modification necessary to anything is cutting the drive rod spring by about 40% of its length to accomodate the MI barrel nut.  I've got a pistol and 2 midlengths and a rifle out there that I've built using these components, and  they all run like sewing machines.

SO, OP, hope this actually answered some questions for you, and leaves you feeling good about the choice to go piston.  As I alluded to before only one has gone to battle, and that is the DI, but only in the AR platform.  Every other battle rifle for the last 70+ years has been an external piston-driven gun for the US.  The M-1 Garand, the M-14, the M-1 carbine, all piston guns.  Add to that the FAL, the AK series, and all the new players like the FN SCAR and the HK 416, the Tavor, and a multitude of other current designs all use an external piston.  Even Eugene Stoner's next design after the AR was an external piston design.  In other words there is a reason it is so popular, it simply works.

So fear not the naysayers, do what you like, and enjoy it however you choose to drive it.