Advice on this for a build. That new Ruger 556 is getting really good reviews and it's not a gas bloc . What are the advantages of gas vs. Direct Impingement?

I think you've got your nomenclature a bit messed up.  If I'm reading it correctly, you're asking the difference between direct gas impingement system and gas piston system

DI has worked for years.     Take notice. All these manufacturers that made these bad ass piston rifles are now getting back into DI guns.    Cause it just works.

My personal take is that pistons are great - when you design the entire weapon system around using a piston. The AR was designed around the DI system.

My personal .02 after working through about 15-20 builds for myself and others:

Piston is a great system if you are running full-auto in the sand storms of Afghanistan. Is it more reliable? Is it more dangerous to get run over by a big rig with a loaded trailer or an empty trailer? People will say that piston is "more reliable," but it's just building up gunk in your gun in a location that's more difficult to clean. All of my builds have been D.I. gas, and I've never had a single failure to feed, eject, fire, etc. I've run hollow points, light loads, heavy loads, heavy bullets, light bullets, and even a 7.5" pistol AR in 223. I've never had a single failure of any kind in any one of my AR's or those I've helped others build. Am I bragging about my builds? Absolutely not. I'm just trying to give you an idea of reliability and maintenance between the 2 options.

In the end, this is your build. If you build a 100% reliable D.I. gas rifle, are you still going to wish you built a piston? If you build a 100% reliable piston, are you going to wish you'd saved the money and built a D.I. gas? That's completely your preference. Use my comment as nothing more than some internet gun nerd giving his personal experience. You do you and do it your best.

I have built quite a few AR's over the years, and I have built a couple with the AA piston system.

DI is perfectly reliable if you use quality parts. One of mine ran 2500 rds in a class and the hard chromed surface of the Bolt and Bolt Carrier looked like it had been powder coated black. Still ran just fine, cleaned up nice, and didn't give me any issues.

AA Pistons are reliable as well. I don't regret building the few that I have, and I still shoot them, but they aren't any more reliable than my quality DI guns. They did cost more, but except for the KISS carbines that just live in the back of the safe, the extra $200 into a piston didn't make that much of a difference in the cost of the gun. Quality parts are expensive.

It also depends on what you are doing with said rifle.
Long range precision semi? I'd go DI. All day everyday.
Shorter range blaster? Take your pick.
Suppressed SBR/PDW? I actually give the nod to pistons here simply due to the location of the gas venting...

Long and short of it?

Build what you want. It's only money, and you can always make more.

This is my first build...AND my first AR. lol. Easy on the judgement....I'm pretty mechanically inclined and YouTube has EXCELLENT step by step build instructions. My only problem of course is knowledge of components. I ordered the matched upper/lower from Spikes to start with. It's a 4 month delay so I'm looking around for parts and trying to decide general direction on a couple things. For sure...I'm not doing a budget build. I want the best parts I can get. Some of you sound pretty in the know so as to speak and what I'm hearing is DI.  That correct?  Don't be shy about it. I can always go back and swap parts if I don't like it.

Just to kind of emphasize what I said above about system design. I look at a comparison of HKs more recent platforms, that both use essentially the same piston system, but have a different carrier, recoil, and buffer mechanisms behind them. It's mostly based on rumors coming from various places, but there is some factual points, such as proving trials to consider, as well. The track record of the G36/XM8/SL8 system is better than the 416/417/MR556/MR762 systems. Why? Because the first mentioned system was designed to use that piston. The other was that same piston, adopted into the AR platform's buffer and carrier design.

Some people will be quick to say that the HK416 outperforms M4s in those same regards, and I will agree. I would, however, also point out that if the DI M4 was being made with the same material and engineering standards as they make the 416, that the M4 itself would be significantly better - but also at a significantly higher cost to the taxpayers to arm the entire military with it. I'm not saying Colt is endangering the lives of our troops with shoddy gear, either. Just remember that when the government ran M4 PIP and the IC competition side by side, they pre-warned entrants into the ICC that price would be part of the consideration in whether they would proceed with the ICC winner or the PIP.

I prefer the internal piston operated AR15's as opposed to the external versions.

I appreciate the info. I've scrolled through a lot of posts on it and I'm thinking DI is the way to go. Not many people can point to any substantial benefit from going piston. Thanks!

There is no substantial benefit.   And if you do suppressed sbr in 300blk I wouldnt do anything other than DI.

IMO, a piston system in an AR is just a answer to a non problem.

Do they work, sure, but so do DI with less moving parts! YMMV


If you really want a piston system, get a scar.

For your first build AND your first AR, stick with "standard" parts, including the standard gas system.  It isn't really a "direct impingement" system - the standard AR had a piston that's INSIDE the carrier.  It also meters the gas to control functioning of the rifle.  It's a slick system, really.

I strongly recommend going with the standard gas redirection system for a number of reasons.  One of the biggest is that NONE of the piston systems is standardized with any of the other systems.  That means dependence on one manufacturer for parts and support.  Not something that gives me a warm fuzzy...

I own two Adams Arms piston uppers; I built one with their kit and I bought the other as a complete upper.  They both operate fine, and I'm happy with them.  I also have a Sig 716 Patrol Rifle, which features a traditional piston gas system.  It's great too.  But I have not found any substantial benefit from any of these guns.  The complete upper is in 5.45x39, and I went piston with that specifically to limit the amount of hardware that would be exposed to corrosive products from commie surplus ammo.  In practice though it really isn't that big a deal.  

With the standard, redirected gas system of the AR, powder gasses are piped into a chamber within the carrier.  Here they push on the back of the bolt and the inside of the cylinder the bolt rides in, which pushes the carrier backward, causing it to open the bolt, etc.  This tends to cause gunk to collect within the carrier, and for some gunk to be blown into the upper (and lower).  This is not a huge problem if you clean your rifle from time to time. In fact, allowing the gunk to collect on the bolt's tail can actually improve functioning, since the bolt tail seals the rear of the internal gas cylinder.

In comparison, traditional pistons merely concentrate the gunk in one spot: the gas cylinder and piston head.  The ONLY true "benefit" from such systems over the standard system is tha you clean all the gunk up in one spot.  On the other hand, the standard system has NO moving parts that are off the direct axis of the barrel - all of the moving parts are in line with the bullet leaving the barrel, which helps reduce mechanical causes of barrel flip.  Even the lightest traditional piston system has some mass above the barrel, and while not a major problem, this can still cause more barrel rise.

So for your very first build AND your very first AR, I strongly recommend going with Mr. Stoner's design, and leave the more complex stuff for something to mess with later.

Kudos, sir, well played.

THIS is sound advice. Also remember that the AR system relies upon the FORWARD gas pressure on the bolt to relieve rearward pressure on the bolt lugs. The designed system does this... a piston (such as LWRC, AA, etc) does NOT. In a normal AR system the bolt UNLOCKS prior to rearward movement. Yes, it UNLOCKS prior to ANY rearward movement (thus ZERO stress on the bolt lugs). A piston system does not. A piston system relies on REARWARD movement of the BCG to unlock the bolt (NO forward pressure)... so the bolt lugs grind against the barrel extension lugs until it unlocks (as it travels rearward).
A piston system cannot provide FORWARD pressure, which the AR system relies upon, thus you will have premature wear with a piston "conversion".

If you want to read about what breaks over time:
https://www.ar15.com/forums/t_3_118/677135_High_round_count_AR_M4_s__over_100_000_rounds__and_how_they_have_handled_on_our_range.html

IIRC the roller bearing cam pin designed for a piston gun is itself known to break sooner than Stoner's design. Since it's a single source proprietary item, it's a good example of the issues building a piston gun. Spare parts become problematic as the source goes out of business, and most businesses in America don't make it ten years.

The emphasis on piston guns came about because of the extreme dust encountered in the Mid East and the design was immediately blamed as being the problem. However, nobody says exactly where the action "jams up." There are no maintenance alerts in the system pointing a finger to a single item. Even testing by the Army has been flawed where guns supplied by vendors get new magazines but the test standard M4's were off the rack with unit mags out of a footlocker. Retested swapping mags we saw higher numbers of stoppages with shared magazines - pointing the finger to that being the bigger problem. Mags and user maintenance or lack of it causes more issues.

Nonetheless piston gun sales jumped up, for a season, until it became obvious it was more hype than proven. In the big picture, if someone wants the "best," then using a common design with parts available from dozens of vendors seems to be the better answer, instead of hitching a wagon to a "star" vendor who's piston sales are declining in a market where nobody is needing them.

Note this - it's NOT the thousands of service members coming back from the Mid East who are gravitating to pistol as the answer. They used and handled the M4 with few issues. It's the AFTERMARKET CIVILIAN buyers interested in the system. And one thing that can be said about them is that having a gun with cool parts in it rates as importantly as one that is reliable. We see that every day, pics of alternate builds with the current list of hot aftermarket parts that make their snapshot build of the month the hot ticket on the forum. Give it two years, tho, and it's a dated cliche - as all those M4geries are now a few years after that fad.

Don't forget, the AR design DOES have an piston - it's the tail of the bolt, and it presses the bolt forward to counteract the case pressing against the bolt face. Exactly where you do need to have pressure in exactly the right way.

Thank you, thank you, thank you...

I'll be here all night... please tip your server

To elaborate OP,
There is nothing wrong with the standard internal piston AR that Eugene Stoner originally developed.  It is often, and incorrectly called "Direct Impingement" or "DI".  It is beautifully simple, works great and lends itself to greater accuracy potential (all other things being equal) because it adds no additional mass reciprocating, back and forth off axis.

I'm not saying that they don't have their place, that people shouldn't buy them or that external-piston guns can't be accurate.  They have their place and an argument can certaibly be made in some cases, but the standard AR15's will run just fine for 99.8% of people.

Wearing my "been there, done that" T-shirt from Iraq, I can point the finger exactly to the single greatest cause of that problem: ignorant, lazy Joes (and Janes), whose only answer to a function problem in their weapons is to "Dump a fuck-ton more oil in it!" Oil collects more gunk, more gunk creates more problems, so they add more oil. It's a vicious cycle. I saw it happen more times than I like to remember.

None of the leadership knew any better, either, which is why there is no official report on what was causing it. It didn't matter that all of my weapons functioned flawlessly, or that I shared my super secret method with them to wipe off the extra oil after they lube it to prevent sand/dust from sticking to it - they still dumped more on it, and them blamed all of the typical ignorant soldier rumors: Equipment bought from the lowest bidder, rifles made by the Mattel toy company, etc.

Anyway, sorry for straying off topic. I just had to lay that out. Cater your maintenance program to your environment. In wetter climates with humidity, rain, or especially around saltwater, by all means let the oil drip. If you're in dry dusty conditions, wipe the excess away.

My experience is the same - I was mobilized but being MP we didn't use weapons in the wire at GTMO. Reserves and National Guard do a lot of training and have a lot of support units, but for the most part, are NOT trigger pullers. We saw a lot of those coming into the fray and their perspective was oriented about maintaining and cleaning the weapon for storage - not daily use.

Even in the field on Annual Training we would not break down the guns on a daily basis for a lube and wipe down. And by the end of two weeks in the field, 100% of the stoppages could be traced back to a lack of maintenance and too much environmental contamination. When the 1SG or SM doesn't make time in the daily tasks for people to clean their weapons - you get weapons failures. We know all about rotating watches, 50% overwatch, sectors of fire, actions in combat - nobody cleaned their weapons. No emphasis by the Chain of Command or Supervisors. None - until turn in.

The weapons don't fail unless the supervisors fail. Too many Powerpoint Rangers are running the system. We are not a combat oriented structure - in point of fact, 90% of the force structure isn't combat MOS primary trigger pullers at all. So we get 90% of them not cleaning the weapon daily because their leadership doesn't set that standard as being important.

They think it just a waste of time and the soldier could be doing something important, like tastefully arranging the camo netting inside the briefing tent.

Yeah, been there done that.

Another vote for "proper maintenance for the environment" being a major contributor to the external piston fad.  However, there were piston variants before we got more than ankle deep in the Sandbox.  It's a "new and different - so it must be better" sort of thing, most of the time.  Well it ain't better just because it's new and different.  And it isn't actually even new.  Take a look at the AR18/AR180: a Stoner designed system intended for manufacture in locations that lack the aluminum forge/mill capabilities of The Land of the Free.  And there's the Beretta AR70/90 and Daewoo K1 and K2; all are essentially piston ARs.