AR Piston Upper - Not a DI vs. Piston Question

AR/M4 AR Technical Discussion
1

I have a dozen DI AR’s (Colt and LMT) that I have been buying since 1988. I have an extra LMT lower that I would like to put some kind of Piston upper on and try that system out. I have no complaints at all with my DI experience, but I want to at least play around with the piston system which I have not experienced. I don’t need anything special with interchangeable barrel or anything extremely high end. I just want a good basic piston upper with 16 inch barrel.

I have looked at the Adams Arms entry level piston upper online, and I have seen some of the POF offerings. For me this would be a learning experience to see how well the piston system works and compare it to what I know and like with my DI weapons.

Any advice would be appreciated.

2

If you want to try a good “piston” upper, get the HK. Probably the best one there is.

3

Major, I would like to suggest that you consider an upper by Primary Weapons Systems. They are, as far as I know, the only company that uses a long stroke system for the AR. Uses less moving parts than any of the short stroke systems, made in Idaho by good people with first class customer support, and comes with an adjustable gas system. Much lighter weight than the HK to boot. Probably the most underrated premium AR manufacturer of which I’m aware.

I have no association with PWS beyond being a happy customer.

4

I’ve owned two of the Adams Arms midlength piston uppers. In each case I talked myself into buying it on sale. Each one worked fine in 2-3 range trips, each one had different recoil vs. a DI upper, and the second one needed an H2 buffer to be tolerable and was best with an H3 but was marginal in reliability and ejection with an H3. They are functional, and seemed to be made decently. I sold each one of them and obviously decided I didn’t need a piston upper.

If you just want to play around I would go with PWS if you can (never had one, only going by design and reputation) or Adams Arms. I’ve used a friend’s POF on several occasions and have not had any desire to buy one myself.

5

Interesting. I was going to recommended the exact opposite. That you do NOT consider PWS.

I live in Idaho (formerly Boise) and I own a PWS. Had to have one. Several people I shoot with have one and had to have one as Idaho folk.

Most of us, including myself, have had nothing but trouble with our PWS piston systems. Mostly gas related issues. The overall consensus is the older units are better than the newer.

My first hand experience with their CS left little to be desired.

Mine is the .308 (Mk216) but the others in the group are 5.56.

My 2 cents.

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6

I’ve had good luck with a basic adams arms middy. They tend to be less expensive and midway carries spare parts.

7

What about an LMT piston upper to go with the LMT lower? It’s not ‘higher end’ than the receiver :wink:

https://lmtdefense.com/parts/mlcpu
Or, if you already have an LMT MRP, there’s a pistol conversion kit for it.

8

My only complaint with my two Adam’s is the rail selection limitations. Syrac is from the same developer (unconfirmed) or so I have heard. But accomodates most rails.

9

I was looking at the CQB PISTON TOP END. I’m old fashioned and still like the picatinny system.

https://lmtdefense.com/parts/cqbpu

It’s just a pricey item at $1749.00. I have heard nothing bad about the LMT piston system, but I have not done much research on it either.

10

I have a Sig 516 that I’ve been really happy with. You can get the upper in 10 or 16" for $1155

11

I didn’t even think of the Sig piston system. Looks like a possibility as well. As I mentioned, the piston system is something I’ve never used before so I am in the learning phase right now.

12

I have owned a few piston AR’s. The Sig 516 I had ran like a top. The only flaw I have with it is the handguard, I just never liked it. I sold it and bought an MCX Rattler. I own the HK MR556 and the MR762. Both run flawlessly. The downfall is they are heavy and expensive. There is a reason I kept both HK’s. Simply, they work, and work well. That being said, the new MCX rifles are nice setups and far cheaper, but if I am not mistaken, take an adapter to work on a standard lower.

13

I have owned a few different type, and my favorite is the Barrett Rec7. I have a 5.56 flyweight.

14

Rec7s were, and I think still, on sale at EuroOptic

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15

Check out the Wolf piston upper, its like 500 bucks.

16

Official rifle of the armed forces of the Republic of China - Taiwan.

Or at least a civilian version of it.

By the way, Midway USA has the MCX uppers with AR receiver adapters in stock today.

17

I would suggest taking a look at the PWS offerings. Robust system, lightweight, accurate…love ‘em

18

I have shot a variety of piston system ARs. I can’t recall all of them at the moment. But the PWS guns were the best. I like the long stroke design and the build/manufacturing quality is excellent.

Joe Mamma

19

I have an LWRC, couple thousand rounds thru it. Everything you hear is true…extra weight, recoil, easier to clean, etc. however, it’s a shooter for sure. That said, if I did another piston gun, it’d prob be the PWS for the long-stroke system, and other things mentioned above.

20

For those of you with PWS piston systems…where does it expel the excess gas it bleeds off? Outside or inside the handguard?

For instance, the HK416 vents gas up and forward from the gas block. The Colt APC vented out the sides of the gas block in front of the handguard. Neither system dumped excess gas under the handguards/rail setup. The LWRC, Sig, Adams Arms, et al all dump excess vented gas underneath the handguard/rail. May not be a huge functional issue but if you’d like to wipe the carbon off then getting under those handguards can be a bitch, and removing some of those rail systems can certainly be a PIA to just do routine maintenance.