AR gas system choice...

[hmt]

Hey guys, long time lurker on here and I finally made an account mostly because I'd like to join the discussion and I had a question.

I'm building an AR-15, getting parts every week or so to stretch the cost out (I call it my payment plan rifle) and I'm torn about what gas system I want to use. I really like the idea of a piston run gun and was looking at the Adam's Arms uppers that go for around $650. I want a really reliable gun. But I notice that some people say the DI guns are fine, just clean them. To get an upper the price will be close to the same for a PSA or similar.

I plan on taking this rifle to classes and shooting it quite a bit; it'll be my first semi-auto rifle. I want a gun that I know will work and I don't mind it getting dirty/scuffed/scratched etc..

If you had to pick a system for your first rifle with the intent of taking classes with it, defending your home and just having fun at the range; what would it be?

 

[dprice3844444]

gotta remember logistics in case of malfunction.if adams arms go belly up,where ya gonna get the parts.

 

[benzy2]

This is just my opinion so take it for that.

If you want a piston rifle, buy one that was designed from the start for a piston. If you want a DI rifle, buy one that was designed from the start for DI. The piston kits for the AR have been very hit or miss, many being less reliable, some causing wear issues in areas not typical to a DI system, and others being done well. I have not seen enough that shows consistently that a given piston system for the AR outperforms the DI setup.

If you want a reliable rifle, buy parts that are high quality and all fall in the TDP/Milspec/The chart or have a good reason to vary from it. That's not to say any rifle that isn't 100% to spec is junk, but that many of the components that make up the Milspec requirements are done for reliability and durability. Parkerizing under the front sight base is not an issue that seems to matter much. Having a bolt made of the proper steel that has been tested, as well as a carrier that uses the proper type gas key fasteners and proper torque/staking on them is important. Understanding the famous "Chart" and why the different items listed do or don't make a difference is the first place to start. Once you understand that, you will have a good idea as to what matters to you and what doesn't.

For reliability I would make sure your get a barrel from a company that is known to use the correct size gas port hole for the gas system length being used. Also, don't go cheap on the BCG. Buy a reputable brand that is known for quality. Many are done right and many are not. Skimping on the BCG is an easy way to ask for problems. From there, I would use an appropriate buffer weight and spring, and a non-adjustable trigger. There is more to the system than that, but having proper gas flow, a proper buffer, a trigger system that isn't going to change setting, and a bolt/carrier that is properly built will keep things running as long as possible.

I've found AR's to be very reliable. They aren't prone from problems, but with minimal proper cleaning and maintenance as well as proper lubrication, they tend to run without stops for periods longer than I have ammo to shoot. There are many cases of torture tests/class rifles that go 15-20k rounds without cleaning. They do get proper lubing as well as springs and bolts (not the entire carrier, just the bolt itself) replaced in that time frame, but no/little cleaning.

If I had to pick one setup for classes and use at home it would be a Colt 6920. Not the fanciest, maybe not the absolute best quality or the best bang for the buck, but it has been the gold standard for years and is the bar others are measured against. I like PSA mentioned above and own both a complete rifle of theirs as well as an upper and upper parts. That said, their QC is mediocre at best. It's not a rifle I'd buy to trust my life with. I bought mine to plink at the range and the other to punch paper at the range/hunt in the open fields. Neither set of uses requires the rifle to function for me to keep living. For that use, as well as for hard use carbine classes, I'd much rather take the quality and long running standard of the Colt over a budget based supplier.

 

[X-Rap]

If you had to pick a system for your first rifle with the intent of taking classes with it, defending your home and just having fun at the range; what would it be?

I'd look at the millions of M4's M16's and AR's out there and buy good quality parts and go DI or else build an AK.

 

[MistWolf]

I could simply tell you simply save money and buy a DI system, but I would just be giving you a fish, a small one that's been laying out in the sun a little too long. You'd be far better served with a few facts and considered opinions to make up your own mind

I picked the original AR piston system in mid-length. Here's what an AR piston looks like
View attachment 672146
The AR piston is part of the bolt and rides inside an expansion chamber (cylinder) in the bolt carrier. As you can see, it's even got piston rings. Truth is, it's not a direct impingement system. A DI system uses gas directly on the carrier, with no piston or expansion chamber. Gases come down the gas tube, hit the carrier and sends it off. The Swedish Ljungman is a classic example of a direct impingement system
View attachment 672147
View attachment 672148
Eugene Stoner used a different approach. Instead of just blasting the carrier with gas, he used a piston. He took the piston out of the gas block and placed it inside the carrier, eliminating the op-rod. This reduces the amount of heat the piston is exposed to and gives it more surface to deal with that heat. It also keeps the reciprocating mass inline with the recoil and bore to reduce muzzle disturbance.
View attachment 672149
Neither system is cleaner, dirtier, hotter or cooler than the other. The difference is where that heat and dirt is vented. The bolt & carrier of the legacy system doesn't run much hotter than that of the PIGB (piston in gas block). With a PIGB more fouling is seen around under the handguards and the gas block. With the legacy system, more is seen in the receivers. Both run fine. The legacy system has had more years of development to work out the bugs.


All else being equal, recoil energy will be the same. It will feel different because of how it's distributed, but it the amount of recoil the round generates is the same.

Practical accuracy will be comparable with an edge to the legacy system if you're shooting bughole groups. Weight should be within a few ounces of each other. Some PIGB upper are heavier, but you'll note those have a thicker barrel profile.

Where you're choice really lies is cost. If both types cost the same, it's your choice as long as the upper is proven to be reliable. Usually, PIGB uppers cost more and offer no real advantage over a legacy upper.

Fort more information, check out the link to Stoner's original patent found in this thread I wrote at M4Carbine.net
http://www.m4carbine.net/showthread.php?t=99050

Here is the rifle I run for HD. It'a a PSA carbine kit that I assembled. Barrel is stainless steel government profile with a 1:8 twist and 223 Wylde chamber. I chose this kit because it was affordable and the important parts were up to spec. After sending the upper back for problems with the feed ramps, it's run reliably every time. I chose this configuration because it's the shortest I could go without having to pin the muzzle device. I like the fit and feel of the Magpul furniture and the H1 Aimpoint is fast, rugged and reliable with a very long battery life. The Battlecomp compensator helps keep the muzzle flat without being as obnoxious as a brake. I mounted a Surefire 300 for when it's dark. It's small, light and very bright for it's size. Burn time is about 4 hours or so. Mounted at the 12 o'clock position, it's easy to switch on & off and the barrel shadow is out of the way
View attachment 672150
I hope I've given you more just a fish, but enough to cast for further knowledge until you know enough to make the decision for yourself

 

[chicharrones]

I'm an AR newb. Even though I've fired a few ARs through the years, I never felt compelled to own one until recently.

I looked into DI gas and piston gas ARs. From what I could tell, the heat and burned powder either end up in the bolt carrier of one or in the piston area of the other. Either way, they both have to be cleaned and both areas get hot.

Since I'm not going to own a select fire* AR, I figure I won't shoot enough to worry about the bolt carrier group and bolt to get hot enough or fouled enough to matter between cleanings. Plus, DI gas systems are for the most part less expensive guns from what I've seen. Anyway, I went with DI gas on my first AR due to those reasons.

Considering picking type of DI gas system, I went with a mid-length type on a carbine length barrel after much reading about the topic.

EDIT: *Even so, the AR was designed to be select fire, so my point doesn't mean much I suppose.

 

[HorseSoldier]

I never had a problem keeping a DI-equipped M4 or M4A1 running in nasty places like downrange with way, way less babying and maintenance than duh intrahweb leads people to believe is necessary. Get a quality AR or components thereof, either way, and you'll be fine.

 

[HKGuns]

If you want a piston rifle, buy one that was designed from the start for a piston.

Blam.....Best advice yet. Do not get a conversion kit to turn a DI rifle into a piston rifle. Unreliability will soon follow.

I own both and have yet to shoot my piston equipped rifle as it was purchased on Saturday. Both will work well for most common use cases. There are plenty of folks taking classes with DI rifles and most appear quite happy.

Since you're on a parts payment plan I would likely opt for DI as it will be less expensive. Build your DI rifle first, (which is what I did as well) then spring for a piston later. The best answer is to have one or more of each.

I posted pictures of my piston AR in the picture thread just an hour or so ago.

 

[Auto426]

I agree with everything Benzy2 said. Slapping a piston on an AR that was ment for DI operation does not automatically net you a more reliable gun. A DI gun built with quality parts and provided minimal maintence will cover just about any need that may arise.

 

[kwguy]

I never had a problem keeping a DI-equipped M4 or M4A1 running in nasty places like downrange with way, way less babying and maintenance than duh intrahweb leads people to believe is necessary. Get a quality AR or components thereof, either way, and you'll be fine.

Ditto.

In addition to DI, I also have an Adams Arms system, and I will say that it's easier to clean, and runs cooler than the DI rifle; however, it's reliability is not the same with differing types of ammo (wolf, steel cased, etc) which may or may not matter to you.

One thing to consider for a DI rifle is a coating system like NP3 / Failzero. I've found that system to be very reliable and easy to clean.

The usefulness of those types of systems (pistons, coatings) fall mainly into the convenience / cleanliness category, more than providing any real operational advantage. At least for me anyway.

 

[CharlieDeltaJuliet]

I have a piston gun (Hk) and will tell you to be very wary of Adams or other piston "conversions". If you want a piston gun you need one that was built from the ground up to be a piston gun, like the Hk, LWRC, Sig 516, etc. other than that I would avoid a piston gun like the plague. The DI guns will do almost everything a piston gun will. Unless you specifically want a piston gun or are going to be shooting in very fine sand, Suppressed or extreme conditions, the DI gun will never fail. Trust me go buy a DD,LMT,Colt,etc and be happy. 99.98% of people would never notice the difference or need the benefits of a piston gun. But make no mistake the Piston guns were designed to run cooler and suppressed . The cooler and cleaner isn't about convenience it is about avoiding wear on moving parts. But are you really going to put 40k rounds through a AR rifle? Most people wont and the cost will not outweigh the benefits if you don't, run suppressed, lots of rounds, and the very most extreme conditions possible.

I have many,many rounds through both and I will be the first to say that you would probably be better off with a GOOD DI gun. Now the ground up piston guns fire anything you put in them and fire better suppressed. I am not going to get into a big pissing contest about them with everyone, but the DI guns are the best all around choice for most people.

 

[MistWolf]

I guess we're continuing to ignore the fact the Stoner system already has a piston?

...From what I could tell, the heat and burned powder either end up in the bolt carrier of one or in the piston area of the other. Either way, they both have to be cleaned and both areas get hot...

How hot do you think the carrier & bolt get?

 

[Quentin]

Great information as usual, MistWolf! And a nice build. I believe you've mentioned before you use the Mossie Midnight Mount for your light. I have that mount on two ARs and have been pleased with them.

Hmt, I don't see how you're going to get an Adams upper for the same price as PSA configured the same (except for the gas system).

Anyway, a PSA 16" midlength would be an excellent choice in an upper. It would come with an FN barrel and you can choose the profile: government, lighter, or pencil (LW). Pencil is about 4 oz lighter than govt and 2 oz less than the lighter profile. My PSA has the lighter profile and my BCM and Daniel Defense have pencils (all three are 16" midlength). Pencil makes the most sense if you want a light, maneuverable rifle. Stainless is a good choice too but not required.

 

[CharlieDeltaJuliet]

To me the Piston vs DI was always like the Hammer vs the Striker fired pistol debate. A person must choose which is right for them. Both do the same job, some will argue one is better than the other, but usually both serves the purpose just fine. One might be right for one person and not for the other.

I still think the OP would benefit from a GOOD quality DI gun. Just mt $0.02, and trust me that's all any opinion is worth. It comes down to he needs to choose the system that is best for him and his use.

MistWolf, great write up. Very good information.

 

[henschman]

If you had to pick a system for your first rifle with the intent of taking classes with it, defending your home and just having fun at the range; what would it be?

High quality, mil spec or better, regular DI setup, 16" pencil profile barrel, mid length gas.

You don't even need to clean a quality DI AR to keep it reliable... just lube it. Keep that bolt wet and it will keep on taking care of business.

I like PSA rifles personally. They seem to be the best value in a mil spec AR.

 

[MistWolf]

Great information as usual, MistWolf! And a nice build...

Thank you on both accounts. The rifle isn't any different than most others but it's a configuration that works. It's basic and simple. I like basic and simple

I believe you've mentioned before you use the Mossie Midnight Mount for your light. I have that mount on two ARs and have been pleased with them...

Yes. Yes, I have. Still running the Mossie Mount and still very satisfied with it and the light. No foreseeable plans to change it out, unless I go with a rifle length carbon fiber free float tube and whack the FSB

 

[HKGuns]

I guess we're continuing to ignore the fact the Stoner system already has a piston?

Kind of sounds like you're looking for a fight on this one Mist. I'm froggy.

It's just great that you pulled the Stoner patent and all and figured out the bolt of the AR is actually a piston AND bolt. Pretty much common knowledge at this point and all of the people who own piston rifles have recommended DI....Yet you still continue.

How hot do you think the carrier & bolt get?

-After how many rounds and at what sustained fire rate? Answer: No matter how many rounds, hotter than a piston rifle. Ever melt a gas tube?

Neither system is cleaner, dirtier, hotter or cooler than the other.

It's a simple matter of where you want your heat and dirt. Do you want it in your receiver and on your bolt where it can and will eventually interfere with feeding and reliability or worse crack your bolt from the stress of hot / cool cycles? Or do you want it outside the barrel and in the hand guards where the odds of it cracking your bolt or requiring copious amounts of oil are remote.

There, you and I have now sent this into the Piston / DI death spiral.

 

[JustinJ]

If you had to pick a system for your first rifle with the intent of taking classes with it, defending your home and just having fun at the range; what would it be?

If i'm defending my home with it, i'd want an sbr and therefor definitely a piston system.

The AR piston is part of the bolt and rides inside an expansion chamber (cylinder) in the bolt carrier. As you can see, it's even got piston rings. Truth is, it's not a direct impingement system. A DI system uses gas directly on the carrier, with no piston or expansion chamber. Gases come down the gas tube, hit the carrier and sends it off. The Swedish Ljungman is a classic example of a direct impingement system

It really depends entirely on one's definition of a piston. In most machines with a piston, the piston is there to impart force on another component. In an AR, the bolt is the end component so calling it a piston is questionable. With a loose enough definition we could call a cartridge a piston. Really, it's all an argument of semantics and therefor contributes nothing to the discussion.

Neither system is cleaner, dirtier, hotter or cooler than the other. The difference is where that heat and dirt is vented. The bolt & carrier of the legacy system doesn't run much hotter than that of the PIGB (piston in gas block). With a PIGB more fouling is seen around under the handguards and the gas block.

Except with a DI gun there is very little "venting". The carbon gas enters the receiver where it cools and solidifies. Regarding a piston system, who cares if its under the handguards? It can't impart resistance to operation of any components there. And since the cavity gas enters from the barrel is much smaller in a piston gun far less enters the action as well. Once the piston finishes its rearward travel the pressure in front of it rapidly rises so less gas enters from the barrel.

If you want a piston rifle, buy one that was designed from the start for a piston. If you want a DI rifle, buy one that was designed from the start for DI. The piston kits for the AR have been very hit or miss, many being less reliable, some causing wear issues in areas not typical to a DI system, and others being done well.

Agreed. I'm not a fan of the slap on kits. My favorite piston gun is probably the PWS primarily because I like the long stroke operating system.


I'm not knocking DI AR's. With standard civilian barrel lengths and the limitation of semi-auto fire a properly built DI gun will meet the needs of the vast majority of civilians. Any advantage a well made piston system offers in such scenarios will rarely, if ever be observed. Now if we chop the barrel, slap on a silencer and run full auto, well, that's another story.

 

[hmt]

Wow! That's a lot of information, everyone had great input. Thank you all for your write-ups and I appreciate it greatly. After considering for a bit, I think I'll be after a PSA or BCM upper and I'll look into the coated BCG's. I can't do an SBR in my state unfortunately, so a 16"bbl with mid-length gas system seems like the best option.

 

[Quentin]

We can call it piston vs. DI or call it front piston vs. rear piston. I'm not going to argue that. (But the piston rings on the bolt is a durn good argument!)

However, for somewhere around 99% of civilian AR users, the standard gas system works very well so research thoroughly whether the "new gas system" is truly worth the extra cost (for your applications).

Now if you want to go SBR, Full Auto or suppressed then maybe you fall in that small percentage - but do it right, no slap on piston kits, buy a well engineered "piston" AR that was actually designed for the "front piston".

 

[HKGuns]

Good choice OP.

 

[chicharrones]

How hot do you think the carrier & bolt get?

Not hot enough to matter to me with my usual rate of fire, which at the extreme would be to smoke the oil off the barrel under the handguard.

I have seen a few interesting videos of people taking temp readings between the piston ARs and the DI ARs. I figure I simply won't lay my finger on the DI bolt when it's hot. Not like I would with a piston gun either, even though it runs cooler.

 

[Quentin]

Htm, I was interrupted while posting so didn't see your post till now. Yes, a BCM or PSA 16" midlength upper is an excellent choice. I have both and they're keepers. I have BCM BCGs in both so there's little to complain about with either. Even the PSA (FN) M4 feed ramps are perfect.

I wouldn't get a special coated BCG, that's not important compared to the technical specs of the bolt and carrier. BCM is a sure thing, look at the specs of their BCG! The PSA Premium BCG should be good too. It has their logo on the carrier and an HP/MP bolt. They have three other BCGs that fall short of the Premium.

Good luck and a look at barrel profiles of the 16" midlength, described in my post last night.

 

[Fishbed77]

My opinion - just get a good quality DI rifle (Colt, BCM, DD, Spikes, LMT, etc.) and be done with it.

If you want a piston rifle, get a SCAR or AK.

If I really felt I HAD to get a piston AR, I guess I would pony up and get an HK MR556a1 (not that I could afford one). Since the HK 416 has been adopted by the USMC (as the M27) and some special operation outfits, I assume it stands the best chance of becoming a "standard" piston AR platform.

 

[Bartholomew Roberts]

After 5 consecutive mag dumps, the Ruger SR556 bolt was around 86F, the Colt LE6920 was around 126F after the same test. So about 40F cooler at the bolt (which does after all seal the breech end of the chamber and see some high temperatures).

If there is any evidence that continued exposure of temperatures less than 200F contributes to earlier failure in Carpenter 158 steel, I have not seen it yet. So I'd say that the idea that a cooler bolt lasts longer is speculative at best. Having said that, systems designed as pistons from the ground up aren't taking a bolt designed for a 20" rifle and gas system and cramming it into a shorter barrel and gas system that dramatically increases the loads. Those systems are designed from the ground up to work with those pressures. So those bolts are probably going to see a longer life compared to a standard M4 bolt.

Not that either one is likely to fail for 99% of shooters.