Which is better and why? Direct Impingement Gas or Piston Operated?

[Veteran]

I am thinking of buying or building a .308 AR10. I want a 24 inch barrel on it. So, one decision I need to weigh is if I want it to be reliable and
operate smoothly even under rapid, repeated firing, AND I want to be able to shoot small groups with accuracy of at least 1 MOA preferably
a half or 3/4 MOA, should I go for gas impingement operation or some type of piston system?

What should I do and why?

 

[DoneNOut]

DI - You will have a rifle length gas tube, pair it with a Superlative Arms adjustable gas block and a 5oz buffer. This would be a smooth shooting set up.

Piston - More expensive, eliminates the buffer, and hopefully has a gas regulator like an FAL.

AR10s are by design with larger 308 cartridge are inherently over gassed.

 

[P7M13]

For piston, I would buy the highest quality bolt and upper receiver you can afford to minimize wear and gauering by carrier tilt.
For DI, you'll be using a rifle length gas system, but on a 24" barrel, you will want an adjustable gas block to tune the cycling.
I use both Odin and JP adjustable gas blocks, and find the JP is a much better adjustment system.

If you plan on using a silencer, go piston. Your eyes and face will thank you.

What will really make a difference in your accuracy:

• Your choice of barrel manufacturer and the quality of the chambering
• The squareness of the upper receiver face where the barrel extension mates.
• The strength, sturdiness and alignment of your hand guard, especially if you're using BUIS
• Your bolt. Stay away from cheap Chinesium junk.
• Your trigger. For rapid repeated, look at the Geissele S3G. There are others too.

Finally, tune your ammo. I've been playing with 308 147gr plinkers (i.e. crap bullets) out of a 16" Ballistic Advantage barrel. Standard loading, I'm happy with 1 to 1-1/2 MOA. Playing with a ladder the other night, I found at high velocity, showing pressure signs, I'm <1/2 MOA. So, my plan is to find that velocity using LC 7.62 brass rather than 308 brass.

Edit to add: it's a stretch to call it a ladder, more like OCW group testing, fifty rounds, five rounds at each charge weight, looking for vertical dispersion. The last group, exhibiting high pressure signs, were all touching.
Also note, not all barrel chambers are equal. The BA 308 barrel was tight. Of my "sight in" rounds (20 rounds at 49gr of PP2KMR), all will pass my check by a Lyman case gauge, but easily 1/3 failed to chamber in my barrel (failing the "plunk" test). Evidently I need to invest in a small base sizer.

 

[asd9055]

Easier to build, find parts and accessories! DI
Reliability, but rare parts, Piston!
I grew up with piston and own both! Including an FAL

 

[moses42ak]

I have never seen anything that would prove that one is more reliable than the other. I believe it's a matter of personal preference but with the AR10 platform you'll be limited in the number of piston options available and none in the aftermarket. POF has a great product. I run the Superlative piston system on my 6.5 Grendel and it's a sub half MOA rifle with factory ammo. Pick which one you want to run and have a good time.

 

[Veteran]

I have heard the piston systems may be more reliable and clean.

I think many if not all military semi autos early on were piston systems.

Ive heard the long piston system may be better than the short piston systems. Any thoughts on that?

 

[asd9055]

I have never seen anything that would prove that one is more reliable than the other. I believe it's a matter of personal preference but with the AR10 platform you'll be limited in the number of piston options available and none in the aftermarket. POF has a great product. I run the Superlative piston system on my 6.5 Grendel and it's a sub half MOA rifle with factory ammo. Pick which one you want to run and have a good time.

Perhaps you need to read more. Direct impimchment is more prone to malfunction due to dirt, dirty powder, infrequent cleaning. That is why the "forward assist" was added after the problems in Vietnam and the "cleaning" kits and training that came after the disaster. Just talk early Vietnam verterans.
Piston, like the M1, FN-FAL, G3, G5, M249 light machinegun (HK 91, 93 for civiallian) and the Sig like SG550 of the Swiss Army and the AK47, AK74, just take more dirt and abuse. Not an opinion, but a fact.
Piston also tend to be heavier.
But like I said above, DI, easier to find parts and accessories here! Easier to build!

 

[moses42ak]

Perhaps you need to read more. Direct impimchment is more prone to malfunction due to dirt, dirty powder, infrequent cleaning. That is why the "forward assist" was added after the problems in Vietnam and the "cleaning" kits and training that came after the disaster. Just talk early Vietnam verterans.
Piston, like the M1, FN-FAL, G3, G5, M249 light machinegun (HK 91, 93 for civiallian) and the Sig like SG550 of the Swiss Army and the AK47, AK74, just take more dirt and abuse. Not an opinion, but a fact.
Piston also tend to be heavier.
But like I said above, DI, easier to find parts and accessories here! Easier to build!

I've read plenty. And I've SEEN more. Each system will have their advantages and drawbacks. I personally run piston systems on all of my AR platforms for my own reasons. Given your logic there would be no need for a forward assist on a piston system but they all have it. You forgot to list the new M4 the military is transitioning to, which is a piston gun. Given what appears to be an oversight of what you seem to believe in your vast knowledge I figured I'd throw that in there for you.

Cheers

 

[Deleted member 115360]

Yeah, there is no debate about reliability, the piston driven platform is significantly more reliable and will run forever with minimal maintenance. I bought a pws ar10 from a member of this forum, and before I did, I was researching the model and found 2 or 3 different stories of guys claiming to have fired thousands of rounds through their rifle without ever doing anything but spraying some oil on the bolt, and never having a malfunction. I have a few of both platforms, and the only benefit to DI is cost and availability. Piston is cleaner, more accurate, less recoil, and functions much better suppressed.

 

[Deleted member 115360]

Perhaps you need to read more. Direct impimchment is more prone to malfunction due to dirt, dirty powder, infrequent cleaning. That is why the "forward assist" was added after the problems in Vietnam and the "cleaning" kits and training that came after the disaster. Just talk early Vietnam verterans.
Piston, like the M1, FN-FAL, G3, G5, M249 light machinegun (HK 91, 93 for civiallian) and the Sig like SG550 of the Swiss Army and the AK47, AK74, just take more dirt and abuse. Not an opinion, but a fact.
Piston also tend to be heavier.
But like I said above, DI, easier to find parts and accessories here! Easier to build!

I take issue with the idea that the M249 will take more dirt and abuse. Ask anyone who ever served in an infantry unit and they will tell you that those dang things have to be cleaned and lubed constantly, and they still malfunction constantly. You can always spot the saw gunner in an infantry squad because he's the guy with the multitool on his belt. It's necessary to keep those things running.

 

[asd9055]

I've read plenty. And I've SEEN more. Each system will have their advantages and drawbacks. I personally run piston systems on all of my AR platforms for my own reasons. Given your logic there would be no need for a forward assist on a piston system but they all have it. You forgot to list the new M4 the military is transitioning to, which is a piston gun. Given what appears to be an oversight of what you seem to believe in your vast knowledge I figured I'd throw that in there for you.

Cheers

"Given your logic there would be no need for a forward assist on a piston system but they all have it. "
Makes no sense, My FNFAL, AK, CETME, SIG piston, the Bren I had in Basic, the M1 Garand, I don't recall any with forward assist...maybe my memory is failing me
Just because I did not list one you know, there are a lot more I did not list. I listed some of the ones I either own, trained on or at least fired!
But is ok...I am done with this subject....

 

[asd9055]

I take issue with the idea that the M249 will take more dirt and abuse. Ask anyone who ever served in an infantry unit and they will tell you that those dang things have to be cleaned and lubed constantly, and they still malfunction constantly. You can always spot the saw gunner in an infantry squad because he's the guy with the multitool on his belt. It's necessary to keep those things running.

OK, I agree, but compare it to a similar one with Direct Impinchment...I don't know of one in that class...is there?
Don't compare it with blowback...

 

[Deleted member 115360]

No, I agree with the principal of your statement, and everything else on your list, but I have a particular hatred for the M249. The tolerances were too tight. A good military automatic weapon should be a little sloppy. Plus, there isn't a reliable way to feed them. All methods are a poor design. But that is specific to that weapon system..

OK, I agree, but compare it to a similar one with Direct Impinchment...I don't know of one in that class...is there?
Don't compare it with blowback...

 

[Veteran]

Does anyone believe DI would provide better accuracy or smaller groups than a piston system,?

If so, is my decision then a trade off in reliability vs. accuracy?

Can I get both?