Gas Piston vs Gas (direct) Impingement

[ProtoPatriot]

Just wanted to get a discussion or whatever on this to supply people information on the 2 systems should they be in the search of their first AR-10/15.

Each has it's benefits and downfalls.

Gas Piston tends to cost more than Gas Impingement.

Gas Piston tends to have a cleaner receiver, which is one of the primary things to keep in clean working order. So, this will lead to a bit longer life span.

Gas Piston tend to be a touch heavier due to the extra parts.

Neither is a flawed system though as has been said.

I do lean towards Gas Piston, but I do have a Gas Impingement AR.

So anyone else with useful information and reasonable comments, have at it.

[jonm]

most gas piston systems suck to suppress.

[bkoenig]

My .02 is that piston systems are an answer in search of a question.  Just keep squirting in oil and a DI system will run longer than you would believe. 

[FarmerRick]

I have an Adams Arms conversion kit on one of my 16" carbine AR's.
It has the replacement gas key, not the dedicated bolt carrier. Not enough rounds through it yet to make any conclusions, other than I like how nice and clean it stays inside, especially since I mostly shoot cheap(and dirty) steel-cased ammo these days.

I only have a rimfire suppressor so far, so I can't comment on that part... 

[jonm]

Is piston carrier tilt still a problem?

[NENick]

The addition weight and size of a piston system deters me.

[OnTheFly]

REAL men don't shoot piston ARs.  Just say'n.

Fly

[Husker_Fan]

My carbine has a gas piston. Of course, it's an M1.

[DCPrecisionLLC]

The debate over Direct Gas Impingement vs. Gas Piston always leads to some bias one way or another. To really decide you have to take a look at the pros and cons of each style of operation and then decide what is more important to you as the end user under the conditions that you will normally be shooting in.

These are major benefits of the Gas Piston system
*Cleaner operation - The carbon and gas do not vent into the receiver
*Cooler operation - This is the most overlooked benefit of the system

These are the major drawbacks of the Gas Piston system
*Typically heavier than their DI counterparts - Not always true, LWRC SPR's are very light
*More expensive in most cases
*More moving parts

The pros and cons of the DI gas system are then exactly the opposite of the Gas Piston system. People will read articles and blogs written by soldiers and "operators" discussing the greater reliability of the Gas Piston system over the DI system and tell themselves that they need a Piston gun because it is more reliable. The often overlooked factor involved in determining the reliability of those guns is not actually how dirty they were but how hot they became after having a high number of rounds shot through them in a very short period of time. This is where the piston guns will outperform the DI guns every time. Since they don't vent hot gas directly into the receiver they stay cooler longer resulting in higher reliability. Even though your typical AR-15 style rifle can fire a high number of rounds in a relatively short period of time its not always good for it. The military has what is called a maximum sustained rate of fire for all of their weapons. The military issue M4s sustained rate of fire is only 12-15 rounds per minute. Any more than that and you risk overheating which can lead to decreased accuracy, melted / burst gas tube, burst barrel, or cook-off in extreme cases. Cook off is a much disputed issue as well, but if you dumb a "combat load" from your rifle as quickly as possible you will start getting close to dangerous cook off temperatures. Just shooting speed drills between 5-20rds with short breaks in between you will heat up you gun pretty quickly. Leave a round chambered for a few seconds afterwards and then remove it and you will see that the jacket on the bullet will have discolored from the heat of the chamber. This can happen in as few as 100-120 rounds.

So what does all this mean to they typical civilian shooter? Increased reliability is not the reason to justify buying a piston gun. The difference in how dirty the rifle becomes will not effect reliability until you have pushed well beyond 1000 rounds without cleaning. If you are the guy that doesn't enjoy cleaning guns than buy a piston gun and you won't need to clean as often. If you like lightweight guns, get a DI. If you want a cheaper gun, get a DI. If you want a simpler gun get a DI. If you think your going to need to ward off a mass attack of hundreds of zombies, get a piston gun. 

[jonm]

I disagree on a few points. There is less gas that gets into the receiver, but there is still gas that gets in there.


Yes, suppressors exacerbate the blowback issue, but is doesnt create it either.

This video also shows it.



Yes a piston gun will stay slightly cooler, but is it really enough to make a difference as far as reliability? Here is a DI gun with 500 rounds fired in 5 minutes, twice. Barrel or gas tube didnt burst. The handguards caught fire the second 500rd/5min session and he continued to shoot without anything blowing up. I am sure there was a decrease in accuracy, but DI or piston, the barrel is still going to get hot and accuracy will decrease. Bolt action guys agree with that and they dont have any gas system. I am not saying that gas tube burst isnt possible, but it is in an extreme situation.
http://vuurwapenblog.com/2012/08/23/how-to-set-your-ar-15-on-fire/


There is no replacement for proper maintenance.

[jon_schram]

I've used both systems as an operator (soldier and contractor)...they both work.  I guess I don't really have a preference.  Neither system has failed me, and they both require maintenance/cleaning to operate, regardless of what you hear on the internet.

I fielded AR based platforms in Iraq, Afghanistan, South America, and Central Africa and didn't have any major problems.  Some folks did/do, but I have to say that routine maintenance is almost always the culprit.  If something does break, these rifles are generally plug-n-play.  This means you are only down for a limited amount of time.

I've also carried piston platform guns in Iraq and all over Africa.  They require slightly less preventative maintenance to keep them running.  These guns tend to be heavier as well.  If something breaks in the field....its a bad deal.  There isn't as good of infrastructure to support them.  I'm a huge fan of the M14 platform, but you need an armorer who knows his stuff if one goes down.  AK's break too...and since its not a truly modular system you tend to be out of luck until you can procure another rifle.  With the AR platform, if a BCG breaks you just slap in a new one and your good to go. 

The HK416 is a great system, but honestly doesn't offer enough of an advantage over the current system to justify the military switching over.  I dislike how heavy the weapon is (heavier barrel, piston system, FF rail, and buffer assembly).  I don't see it as a significant advantage over the traditional DI system currently in use.

This debate will go on forever.  Eventually something new will come out and we will argue DI vs. Piston vs. Magical new device.  Both systems work well, and they both have their shortcomings.  Pick whatever your happy with and put some rounds down range.

[bk09]

Everybody has seemed to hit the nail on the head so far. One thing not mentioned so far is the fact that a piston creates moving parts on the barrel. This will hinder accuracy a little. If you look up the POF rifles you won't get crazy tight groups despite spending $2k, but you get easy cleaning and cooler guns with sustained fire. The barrel nut on a POF if I remember correctly is 65 square inches of surface area that does a lot to mitigate heat. If you are looking for a piston gun that would be my choice. If you favor tiny groups on paper then a DI would be the route I would go. After messing with Daniel Defense at work I have grown to like what I see/feel on them.

[jon_schram]

Everybody has seemed to hit the nail on the head so far. One thing not mentioned so far is the fact that a piston creates moving parts on the barrel. This will hinder accuracy a little. If you look up the POF rifles you won't get crazy tight groups despite spending $2k, but you get easy cleaning and cooler guns with sustained fire. The barrel nut on a POF if I remember correctly is 65 square inches of surface area that does a lot to mitigate heat. If you are looking for a piston gun that would be my choice. If you favor tiny groups on paper then a DI would be the route I would go. After messing with Daniel Defense at work I have grown to like what I see/feel on them.

All things being equal, DI might indeed hold a theoretical accuracy edge, for all the reasons you mentioned.  In real life it would be impossible to judge this, as each firearm seems to be a law in and of itself.  There are plenty of M1, M1A, FAL, etc shooters that will argue this point as well.  I will say that piston guns can be more finicky...but armorers, competitors, and regular joe's have gotten pretty good at working around these issues.  Proper bedding techniques, gas tuning via regulators, etc. all work to make piston guns accurate enough for social work to competition. 

Some of the downfalls of the extra steel hanging off of the barrel are further mitigated by the potential to have tighter tolerances in the receiver (not as much junk working its way into the receiver to push the bolt back).  Most DI AR15 platforms have fairly generous tolerances to keep them working in adverse/dirty internals.  Of course this is a moot point in military style rifles, as they all tend to have generous working tolerances to keep them going...bad deal to have your rifle gunk up in a firefight.