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Discussion Starter · #1 ·
I’m building a 6.8 rifle and would like to use a piston setup if I can. Already have a superlative arms piston kit in my parts box. What is the consensus here on using their piston kit for a 6.8 upper in terms of reliability? I’ve read some accounts here of members doing it, but superlative arms doesn’t recommend its use with 6.8. Thanks.
 

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I've got over 6,000 rounds through one and it's the most reliable rifle I've hunted with. I just opened the screw all the way with an ARP barrel and never looked back. Runs a lot cleaner than a gas gun.
 

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Discussion Starter · #3 ·
I've got over 6,000 rounds through one and it's the most reliable rifle I've hunted with. I just opened the screw all the way with an ARP barrel and never looked back. Runs a lot cleaner than a gas gun.
Awesome. Then that’s what I’ll do. Fingers crossed it fits under my handguard.

is There any benefit of an ARP barrel over a Wilson combat barrel?
 

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Awesome. Then that’s what I’ll do. Fingers crossed it fits under my handguard.

is There any benefit of an ARP barrel over a Wilson combat barrel?
Not sure what handguard you have but not too many are as tight as the BCM KMR rail. My superlative piston barely fits in it. I believe it’s 1.75” OD vertically and 1.5” OD horizontally.
Biggest thing is making sure the top rail section is milled most of the way out, I have other rails that aren’t and they won’t fit over the block.
 

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Discussion Starter · #6 ·
Not sure what handguard you have but not too many are as tight as the BCM KMR rail. My superlative piston barely fits in it. I believe it’s 1.75” OD vertically and 1.5” OD horizontally.
Biggest thing is making sure the top rail section is milled most of the way out, I have other rails that aren’t and they won’t fit over the block.
I’m using the CMT mod 2 rail. CMT confirmed it will fit.
 

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I would not recommend the superlative arms piston system. There are some fundamental design issues that start to present themselves after the round counts build up.

Maybe if your not subjecting the gun to frequent high volume fire and keep the drive rod well lubed and the gas block cleaned, they may be a minor issue overall, but I've read from a 3-gunner these issues:

1. The return spring is internal to the gas block unlike Adams Arms, LWRC, H&K etc. It's rather small and exposed to all the hot pressurized gases. This causes the return spring to loose it's tension every few thousand rounds.

2. The drive rod is NOT guided like LWRC, Adams Arms or H&K. The piston head is very short, the carrier has a dimple and the drive rod a rounded end (like a ball and cup). While this may seem advantageous, it forces the drive rod and carrier upward and over time this wears out the guide hole in the aluminum receivers.

The 3-gunner I read that used this system ended up using the Adams Arms steel receiver bushing because his upper was so badly worn. All three competing systems from LWRC, Adams Arms and H&K use guided piston cups that slide over a sleeve, so the drive rod doesn't wear out the receiver guide hole as it's guided at two locations.

Makes perfect sense if you think about it, a long rod which can easily pivot inside the gas block, all the force keeping it straight is going to be on the upper side of the other end of the drive rod as it passes through the receiver.

3. The internal gas piston design tends to foul up. While your upper receiver may stay clean, the inside of the gas block becomes heavily fouled, requiring more cleaning than one would think. All three other competing systems (LWRC, Adams Arms and H&K) vent externally.

The 3-gunner who did the review had previously run the Adams Arms system and had no issues. Defensive review has run over 10k rounds without cleaning in the AA piston system without an wear issues. I've used it myself including for a 5.45x39mm AR upper back when 7N6 was available and had no issues.

Superlative Arms designer left Adams Arms because he disagreed with the lead engineer. Apparently the lead engineer at AA knew better because the SA system is problematic when you start to push it. It is lighter weight than AA's or LWRC's designs and you can use standard handguards and barrel nuts, however the trade off is long term reliability and robustness.

And weight / handguard compatibility is the primary reason I actually switch from using AA Piston gas systems to Internal Gas Piston (what most people call DI is not DI). Modern IGP is nearly 7oz lighter than a comparable AA or LWRC piston system and with NiB, Nitride or other plating or case hardening methods on bolts and carriers, combined with one piece gas rings, I think IGP still retains the ultimate balance of reliability vs. weight.

Also consider that while all of these piston systems are "free floating", that's only true when they are NOT pressurized, while the piston is applying pressure against the carrier, it's making a hard and still somewhat violent connection between the gas block and receiver.

IGP systems don't. The gas tube remains free floating throughout the entire cycle and the force on the BCG is still directly inline with the bore. IGP still remains the accuracy king, even though these free floating piston setups can be quite accurate (1MOA), they are not quite at the level of a bolt gun or IGP gas system.
 

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Remember, all the reviews on the SA piston system are over a short duration, most of them at most a few hundred rounds. LWRC, Adams Arms etc. have several reviews showing long term reliability over 10,000 rounds or more in some cases.

Just something to consider. The SA system may fit your needs, but if your a high volume shooter I would not suggest that route.
 

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When I get to 10k or a failure, I’ll follow up on this thread. My opinion on it, seems to be ok design. I had a cmmg piston kit and it seemed to work great through a couple k of 6.8, gave it to my brother in law. The spring inside is not a requirement for operation and it’s a pretty simple design. I can see the wear in the upper as a significant issue. I’m not certain about the gas block getting fouled, seems like it would kind of scrub the bore as it cycles.
The cmmg piston kit was of similar design and I never had an issue with it, it was just too bulky. They don’t make them anymore, not sure why- maybe it is inferior. I got it because it appeared to be a simpler design than the AA kit or others. As always time will tell but in the meantime I’m gonna enjoy the bleed off and soft shooting sob!
 

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That's good to hear yours has held up fine. The upper receiver wear seemed to be the biggest issue overall and that's because the piston isn't guided, it just kinda loosely slides through the gas block where LWRC and Adams use an inverted design that's like a sleeve that slides along the gas port shaft. This forces alignment of the piston drive rod through the upper receiver, but it's still not as good as the original Internal Gas Piston design (aka what most people incorrectly refer to as DI).

However both of those designs require a return spring that rests against the barrel nut or receiver, so it's not compatible with standard run of the mill DI hanguards like the Syrac. The trade off is long term reliability and component wear. Also the carriers are a flat tappet type with AA and LWRC, not a ball and cup which can crack under heavy full auto loads (LMT uses a ball and cup type, we've seen failures too), that probably isn't a concern for your applications, but it's part of the original design intent behind most of the piston systems. It would be interesting to see the upper receiver wear after 10k rounds compared to an AA or LWRC design, or even an H&K 416.
 

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Well, I'm definitionally not a 3-gunner but I am a hog hunter. A thirty round mag dump is common and some times a sixty round mag dump is necessary. I don't know if this qualifies as high volume or not but it's the norm or me.

As far as the spring goes it's not necessary at all. Mine quit functioning after several thousand rounds so I threw it away. It still works flawless without it.

The push rod IS guided not like the three gunner said, also the little socket/dimple helps keep the rod captured just like every engine that has pushrods and rocker arms for valve opening. Adams Arms carrier is not dimpled. I'm way past 10,000 rounds now and I have not seen any upper receiver damage yet from any of my rifles or friends of mine that do run these. I know combined total we have over 25,000 rounds.

As far as cleaning the gas block it's not necessary. It's self cleaning just like the others.

Every thing the 3-gunner said about Superlative Arms piston system was wrong based on my experience with it.
 

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I installed one on one of my 6.8s last weekend. It says the spring and the bushing are not required. Lining up the gas block is very important, and it DOES vent the excess gas out the front and only the amount required to operate the piston is used... So I have no idea what that 3-gunner guy was talking about. Heck its one of the best features about Superlative gas blocks is the venting function. BTW you can use this gas block with suppressors and it makes no difference, once the gas is set it only lets enough through to operate the piston (even suppressed). Its a fantastic setup. Maybe that 3-gunner had a chip on his shoulder or something...
 
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