Question on AR platform, DI vs piston

[whisler]

I have little to no knowledge about AR platforms, but now have an opportunity to choose between 2 different rifles. One is an Adams Arms AA-15, which I know is piston driven and the other is an S & W M&P-15, which is direct impingement. I have 2 questions.

1. What are the pros and cons of the 2 different systems? (I understand the major difference but not the details)

2. Which would you choose between the brands? The S & W definitely has the nicer furniture, but that can all be changed.

My lack of knowledge comes from a lack of interest in the platform until now, due to being an old guy who prefers wood and steel and even better if it loads from the front and uses flint for ignition. But the time comes when even old guys need to catch up, so give me a hand.
Any help greatly appreciated.

 

[<*(((><]

I don’t particularly care for a reciprocating mass located high on the rifle when there is an alternative that provides a linear “piston BCG” close to the centerline of the rifle and the shooters shoulder.

In other words I fail to see the advantage of a piston AR over DI. DI guns have been used all over the world now and have proven their reliability and simplicity of parts.

For ARs the beauty of them is the high modularity, ease of maintaining and the simply ability of swapping uppers in 10 seconds.

Given the description you gave of yourself I would go with the S&W DI gun, it is a great entry level AR which will get your feet wet.

 

[cfullgraf]

There is a lot of discussion on what type of gas system the AR-15 has. If you look at a true gas impingement system, the AR-15 is not it. There is a piston in the AR-15 gas system, the bolt, and a cylinder, the bolt carrier. It is just the piston is stationary and the cylinder moves.

In any case, the AR-15's gas system is pretty simple except for the fact that gasses are released into the action. But, it has worked pretty well for our government for the past 60 or so years.

Gas piston systems are more complex and have more parts but they do exhaust the gasses outside of the action.

Flip a coin but I'll stick with the AR-15 action.

 

[boom boom]

Piston AR's came about because people wanted something different for a variety of reasons. Some wanted piston AR because they fire suppressed a lot and piston actions are generally a bit more adaptable, some liked pistons because of the bad rep AR's got in SE Asia, some like pistons because they feel that they are more reliable as many piston battle rifles are regarded as highly reliable under field conditions, and some want something different than what every Tom, Dick, and Harry have.

The rest is tradeoffs--heat in the upper receiver or at the forend, a bit less accuracy (pistons generally are less accurate) or more, run wet or dry, and so on.

For better or worse, AR's and their parts are largely a commodity now where one can assemble exactly what pieces you want. Piston AR's are proprietary and so you will have to stick with the company that brung it more or less.

The good news, you can have both, apparently you can buy an adams piston upper and put it on your S&W lower. From Adams' website, it appears that you could buy an S&W upper and put it on your Adams lower as well. I also think someone as well as Adams sells a kit to convert or build an upper into a piston system. (Googled it and it is Superlative Arms that does it--may be others as well). The one good thing about standards is that it makes plug and play a lot easier to do.

 

[Waterboy3313]

2. Which would you choose between the brands? The S & W definitely has the nicer furniture, but that can all be changed.

Neither one. I would go to the local gun shop and find a stripped lower and start from scratch. Rather than buy something ready to go and change a bunch of parts. I've put together several ARs and didn't know the first thing about them when I started.

Now I have 5 different configurations for whatever I feel like shooting. My favorite one to shoot is a basic no frills iron sight $400 unit. It's probably similar to the M&P version. If I didn't live in CA the lower could have been ordered online with out all of the hoops to jump through and cost me $50-60 less. Instead I went to the local gun store and bought it over priced for $130 out the door.

 

[edwardware]

I have little to no knowledge about AR platforms, but now have an opportunity. . .

Since this is a first AR, buy the proper AR.

Reciprocating Piston ARs are like Rotary Engine Mazdas; wicked cool toy if you're a motorhead, completely unnecessary complexity and maintenance requirements if you're not.

 

[BSA1]

The M16 & M4 has been used by our military for over 50 years and have no plans to drop it so I am confident in it’s reliability. As I like to build my own AR’s I use the D.I. Gas System. If going store brought I would also take a look at Windham.

 

[Corpral_Agarn]

Standard is my choice.

I like the balance better and haven't had issues with reliability that were not my own fault.

 

[JeeperCreeper]

There's lots of info and opinions out there on this. Most are valid, but some stem from old myths about the M16 in Vietnam.

I like DI but I've never owned a piston. Considered it for fun, but DI guns run very well.

Here's some videos that I watched a while ago. Can't remember how good they are.

 

[Deus Machina]

I'm a piston guy. Why I get an AK, not an AR, so take this all as second-hand. From a purely engineering standpoint, they just tend to be simpler to keep reliable. Especially long-stroke piston systems like an AK, which of course has its own benefits and downsides and neither are entirely the piston.
That said, I don't have anything against the AR. Yeah, maybe they gunk up eventually. But there's no reason a civilian can involuntarily go that long without cleaning it. Heck, it's a rare soldier that won't get the time to clean it for that long.
So grab what feels nice. Then just actually clean your gun now and then and call it good.

 

[NIGHTLORD40K]

I have both. The piston gun runs cleaner, but no difference in accuracy or reliability.

Gotta watch out for your optics getting too close to the gas vents on the piston guns.

If piston parts break, getting replacements could be tough because they arent standardized between manufacturers.

 

[whisler]

Thanks for the replies. Keep them coming. This is all very helpful

 

[taliv]

i don't have any use for pistons in ARs. if you want a piston, get a SCAR or something similar designed around a piston.

 

[NIGHTLORD40K]

i don't have any use for pistons in ARs. if you want a piston, get a AK or something similar designed around a piston.

There, fixed it for ya, lol.

It occurs to me that the Marines' HK 416s are piston guns and AFAIK, they are happy with them.

Any Jarheads here have experience with them?

 

[Catpop]

I often wondered about that. Thanks for thread.

 

[taliv]

hk416 is a good choice but very expensive, and you have the same problem with replacement parts

 

[Skylerbone]

I’m curious why specifically one of those two models?

 

[JeeperCreeper]

I would again like to highlight that as cool as piston ARs are...

Each brand is its own proprietary system.

HK is different than Adams is different than the Taiwanese T91 is different than POF is different than LWRC.

At least as far as I know

 

[someguy2800]

Just my own thoughts but you couldn't give me a piston driven upper. To me its a downgrade in every way. Answer to a non existing problem unless the problem is you want a more complicated and expensive gun that's harder to maintain.

 

[ms6852]

I have no experience with pistons and in all honesty I prefer the other system because I know it well as a majority of us that had experiences with the M16. Only reason!

 

[Pat Riot]

I had a Ruger piston upper, the SR 556. I didn’t care for it. It was heavy which made my AR front heavy. Cleaning wasn’t easier, as advertised. I literally wasted money on it because I hated the thing compared to my first regular gas impingement AR-15. I assembled them both at the same time when I first got into ARs. When I took them shooting the standard AR configuration was my immediate favorite, hands down.
The piston AR weighed over 10 pounds.
The standard AR was just a little over 7 pounds using the same lower components on each.
I have assemble 4 other ARs since, all gas impingement. I have no interest in a piston AR.

If your concern is getting a lot of carbon build up try building a DI gun with an adjustable gas block to regulate the gas coming back into the receiver. All guns get dirty. If it ain’t getting dirty you aren’t shooting it...enough.

 

[Demi-human]

I have a couple of each.

I find the shafted pistons run neither cooler, nor cleaner. (Most of the schmutz comes from ejection, not the scant bit required for operation.)

I find the tubed pistons neither more accurate, nor more reliable. (But I also don’t drag them behind a truck and tend to clean them when they’re dirty.)

I have them because variety is the spice, however, they are more alike than different.

I also have a gas ring/ dual action bar operated one.(That swats your forward hand with gas pressure...)
I just need a pump and a lever action AR, then I will have collected them all!

The proprietary parts do not confront me. The average RangeAR Ranger wouldn’t put a no-name replacement piece in their ubercool JP ultra light BCM ThwackerDaddy 4, anyway.

 

[748]

Get both.

 

[dave951]

One point everybody is missing is to use the correct powder in the ammo. Some powders burn more "dirty" than others. Shoot a DI system with a "dirty" powder, and you'll swear the DI system is garbage. Use a cleaner burning one and it's fine. YMMV That's the source of the initial problems, aside from poor maint.

 

[NIGHTLORD40K]

Get both.

I only got my piston upper because a fella selling jerky at the gunshow happened to have one on his table and the box caught my eye. Since I was in need of an upper of some sort, any sort, I asked him about it.

He said he had taken it in on trade for a dehumidifier and didnt know anything about it, $150......

I opened the box and lo and behold, a complete brand-new CMMG WASP piston upper w/ bcg. These were quite expensive when they were introduced, now discontinued.

I use it on my scoped DMR\ fun gun. Its fine, but I dont dont see any performance advantage to it. I would never pay retail for it, thats for sure.
I would not grab this gun over a DI one for any sort of serious social situation, especially TEOTWAKI, simply because of the lack of spare parts.

Also, the bulk of the piston assembly limits your choices when it comes to handguards, BTW.