AR 15 piston conversion

[c.latrans]

Hey all. So here is the deal, I am possessed of an old school attitude when it comes to firearms...........the ones I love dearest are wood and blue, especially my Sakos! At any rate, I have joined the AR club with the gift of an Armalite M15.

At any rate, I am having way more fun with this thing than I ever expected, and am considering a piston conversion. My questions are for those of you in the know. Treat me as a noob, because they write entire books about the things I dont know about ARs, but I see the advantages of a piston conversion. Is it worth the time and effort to convert my rifle, or should I just trade up? Is the conversion hard to do, and to make work correctly? I am by no means anyone's gunsmith, but I am mechanically inclined and have done some automotive machine work, as well as fairly extensive work on bolt guns, so I am not averse to simple problems. What unexpected treats can I expect to encounter? Anyone with first hand experience on doing a conversion please chime in...............and thanks in advance!

 

[rcmodel]

IMO:
If it ain't broke, don't fix it.

The DI gas system on the AR thrusts the bolt carrier straight back in the upper.

All Piston systems whack it hard off-center of the carrier where the gas key used to be, and cause carrier tilt wear in the soft aluminum upper.

That can lead to eventual functioning problems.

The other thing is, you can get standard AR-15 parts everywhere, except Walmart.
Not so much for some propriety design gas piston kit.

If the company folds their tent and sneaks off in the dark?
Good luck finding parts for that piston upper.

rc

 

[ugaarguy]

If you choose to convert, your first major choice will be which style of piston kit to use. There are kits with small operating rods designed to fit through the existing small gas tube hole on a direct impingement AR upper. Then there are kits which require you to ream that hole larger to facilitate a larger & stronger op rod. Systems of either type will come with either a new bolt carrier, or a strike plate for the op rod that replaces the gas key on your DI carrier.

The theoretical advantages to a piston AR are:
It runs cooler in the receiver.
It puts the carbon fouling on the front of the piston by the gas block.

The disadvantages are:
The reciprocating mass of the piston over the barrel changes harmonics, and typically reduces accuracy.

Piston operation induces carrier tilt because the operating force is now non-linear. When Eugene Stoner switched to piston operation on the AR-16 he kept the AR-10/15 style bolt, but totally redesigned the carrier and recoil spring system to account for the piston drive.

Even though the carbon fouling builds up on the front of the piston, is this really an advantage? In the DI system the carbon builds up on the back of the bolt, inside the carrier - as designed, and not in the chamber as some folks would lead you to believe.

The piston drive does not address the tight tolerances of the small, camming, multi-lug AR bolt.

 

[rjrivero]

ugaarguy,

Are you sure Stoner worked on the AR18 project? I thought he wasn't involved with that design.

 

[ugaarguy]

Are you sure Stoner worked on the AR18 project? I thought he wasn't involved with that design.

rjrivero, you're correct. Stoner's last design before leaving Armalite was the 7.62 NATO AR-16. If my understanding is correct the AR-18 is essentially an AR-16 scaled down to 5.56 NATO, much like the AR-15 was developed largely by scaling down the AR-10.

Anyway, when Stoner & the other engineers at ArmaLite switched from DI to short stroke piston operation they kept the AR-10/15 style bolts heads, but completely changed the carriers & recoil springs.

 

[HKGuns]

I personally wouldn't waste money on a conversion. You're asking for problems that don't exist with your rifle as it is today. I would buy a rifle designed to run with a piston from the ground up. YMMV

 

[briansmithwins]

I'd spend the piston money on ammo or optics.

BSW

 

[toejamm]

c.latrans,
The DI vs. piston discussion really gets things going. It seems guys are either on one side or the other. I happen to be in the middle. I own, and like them both. They each have their pros and cons.
Instead of buying a conversion kit, how about just buying the complete upper? It costs a couple hundred more, no doubt, but that way, pull two pins, and you can switch between the two. You'll get the entire BCG with the new upper so there is no fiddling with the bolt, gas block etc.
CTD, Midway, Brownell's and others have plenty to choose from. I bought an Adams Arms upper for $600.00 from CTD recently, put it on my S&W M&P lower and it works great. Every bit as accurate as my mid90's Bushmaster with the fluted target free float barrel.

Just my 2 cents..............

 

[Z-Michigan]

For 99% of uses the DI system is better. I would leave it be and spend the money on something else (ammo, training, optics, beer...).

If you just HAVE to have a piston, I would suggest the Adams Arms setup.

 

[awgrizzly]

Hey... you think this is going to be your last AR? Shoot it and enjoy. Then when you buy your next (perhaps build one) you can decide on the piston. Right now all I'll say is that the DI is just going to cause you a bit more cleaning, which can be a good excuse to fiddle with a gun on a rainy day. The hard part is cleaning the inside of the dang receiver.

 

[Justin]

Plenty of 3 gun shooters have DI ARs with tens of of thousands of rounds through them and no failures attributable to the DI system.

Personally, I simply don't see any real world advantage to the piston conversions, even for high round count shooters who rarely clean their rifle, and there are at least a couple of distinct disadvantages to them.

Sent from my myTouch_4G_Slide using Tapatalk

 

[c.latrans]

Great thoughts from all of you, exactly the comments I am looking for........especially the potential excuses for a second AR!

 

[JustinJ]

If the ole "if it aint broke don't fix it" attitude were followed there would never be any advancements in firearms. Reliable is a relative term so saying the AR, AK, SCAR, etc is or isn't reliable means nothing without a definition of what reliable means or another model for comparison. Regardless of how one feels about the reliability of the AR there is no question that it is not perfect but neither is any other rifle. The point is there is always room for improvement. So wether or not the AR can be improved with a piston can certainly be debated but pursing efforts to improve the AR is certainly a valid pursuit. One thing to consider is that there are no new assault rifles being deloped that use the DI system. They all use a piston, or at least all that i know of. I personally think in select fire and short barrel weapons the piston system is superior so long as the additional parts don't break and the carrier tilt issue is worked out as the makers claim.

As far as conversion systems the Adams Arms has the biggest following. Many AR makers are using their design in their piston guns. I like the idea of a long stroke system like the PWS and Adcor Defense but there are no conversions available that i am aware of.

 

[MistWolf]

There is no need to add a piston to the AR as it already has one.
View attachment 594960
It's part of the bolt. What the AR lacks is an op rod/piston rod.

Just what does the gas directly impinge on in the AR? The gases go into the BCG (which is a cylinder) and pushes it rearward. The same thing happens on a rifle with the piston mounted at the gas block except it's the piston that gets moved rearward. The AR gas system isn't really a "direct impingement".

The advantage of making the piston part of the bolt is keeping the reciprocating mass inline with the bore and recoil to minimize muzzle rise. Adding a piston rod puts part of the that mass above the bore and ahead the shooter's hands as well as increasing it's leverage. It's a step backwards in recoil & muzzle rise control.

Adapting a piston rod to an AR is like adapting ski poles to a bicycle

 

[toejamm]

MistWolf,

"It's a step backwards in recoil & muzzle rise control."

You can say that if you want. My experience with my LWRC and AArms carbines gives me less recoil and no difference in muzzle rise as compared to my Bushmaster and Armalite carbines.
Unless you can prove what you are saying, I am going to rely on my first hand experience.

"......adapting ski poles to a bicycle." Sorry, I don't get that analogy.

 

[BamAlmighty]

Your always going to have old fogies that can't accept change or learn new tricks... with that said I have DI ARs and GP ARs. I like them all, but I like my GP ARs even better. Especially my adam arms ARs. 1) Not having gases vented out of the ejection port 2) upper receiver, bolt, chamber stays spotless compared to a DI gun 3) even the piston block is easy to clean

Aside from my early Ruger SR556, none of my newer gas piston guns show any signs of carrier tilt after 1000s of rounds.

Going forward, all my future ARs will be piston guns.

 

[awgrizzly]

Your always going to have old fogies that can't accept change or learn new tricks... with that said I have DI ARs and GP ARs. I like them all, but I like my GP ARs even better. Especially my adam arms ARs. 1) Not having gases vented out of the ejection port 2) upper receiver, bolt, chamber stays spotless compared to a DI gun 3) even the piston block is easy to clean

Aside from my early Ruger SR556, none of my newer gas piston guns show any signs of carrier tilt after 1000s of rounds.

Going forward, all my future ARs will be piston guns.

Old fogies... change... new tricks? Hey whipper snapper, seems to me the GP is an old trick. Like, the DI came after the Garand.

Just saying... After all, I have to defend us old foggies.

 

[Robert]

I don't see where it is any better than a DI system. It may or may not be a little worse as some have pointed out but they have not been around long enough to really tell. One story here or there does not render something a go or no go. If you want one get it. There is no better reason than you want one. If it were me I'd spend the extra money on ammo.

 

[BADUNAME37]

I am happy with my AR, it works first time, every time.
Why would I want to spend extra money for something I think would be ten steps backward than from what I currently have?

I wouldn't.
I would rather spend my money on other things, even if just more reloading components so I can shoot more.

 

[Casefull]

Your always going to have old fogies that can't accept change or learn new tricks... with that said I have DI ARs and GP ARs. I like them all, but I like my GP ARs even better. Especially my adam arms ARs. 1) Not having gases vented out of the ejection port 2) upper receiver, bolt, chamber stays spotless compared to a DI gun 3) even the piston block is easy to clean

Simpler is almost always better. Nothing wrong with pistons but they are not an advance only a change. BTW, I am real close to being an old fogie but I love modern firearms. I will take lighter, less complicated, and more accurate anyday...how about less expensive also.

 

[MistWolf]

MistWolf,

"It's a step backwards in recoil & muzzle rise control."

You can say that if you want. My experience with my LWRC and AArms carbines gives me less recoil and no difference in muzzle rise as compared to my Bushmaster and Armalite carbines.
Unless you can prove what you are saying, I am going to rely on my first hand experience.

"......adapting ski poles to a bicycle." Sorry, I don't get that analogy.

First of all, the gas system doesn't reduce recoil. It can change how the recoil feels to a shooter, but it cannot reduce it. The only way your AR can reduce recoil with the same ammo is that the rounds leave the muzzle at a lower velocity or because the rifle weighs more.

All piston rod systems for the AR places the piston rod above the bore. Now you have reciprocating mass above the bore instead on inline with the bore. Stoner kept the reciprocating mass inline with the bore to reduce muzzle rise. It may be that a shooter doesn't discern the difference and that's ok. Still, it's the law of physics that having reciprocating mass above the bore line increases it's leverage and it will have a greater impact on muzzle rise.

As the piston rod conversion shows no marked improvement in reliability, durability or accuracy in an AR, it adds unnecessary complexity, weight and cost for no gain. It also introduces the possibility of carrier tilt causing wear to the receiver extension.

My analogy of adding ski poles to a bicycle doesn't make sense because adding a piston rod to an AR doesn't make sense. The only reason the piston rod conversion has any traction at all is because people have looked at a problem and mis-diagnosed the cause

 

[HKGuns]

I'll use the HK416 as the best piston example to demonstrate whether you need a piston or not.

I think you'll find four main advantages of the HK416 over it's DI brothers currently used by Uncle Sam. (Not all Piston systems are created equal.)

Note: The HK416 uses a short stroke piston similar to the G36 design. Other designs use a long stroke piston which may not have all of these qualities.

1. Higher FA cyclic rate with no gas tube to heat and potentially fail. (~30 - 50)
2. Reliably suppressed.
3. Reliable gas system in <14" barrels. (10.4")
4. Extended service life of some critical components.

If none of these are requirements for you, then DI will work just fine as it has for a number of years. The short stroke piston is a proven system in the HK AR's as well as the G36. Both reliable and battle proven rifles. I don't buy into the conversion idea as stated above. Buy one designed from the ground up to work with a piston. There are plenty of options out there as a second AR. They are more expensive in general.

 

[MistWolf]

PS- If you want me to really go "Old Fogey" on you then my advice is if you want a rifle with a real piston rod, sell that Mattie Mattel instead of trying to turn it into something it's not and buy a FAL, or better yet, skip the piston rod and get an M14 with a real he-man op-rod

 

[toejamm]

MistWolf, it is not my intention to pick a fight with you or anyone else discussing this topic. The OP wants to know if anyone has any experience with GP conversion of an AR weapon. He would like some guidence from us members of THR and that is what I was trying to accomplish.
As stated previously, I have and like both the DI and GP versions of the AR rifle. They both, in my opinion, like all weapon platforms, have good and bad qualities. Call the weapons "Mattie Mattel" if you like............. to each his own.
For the record:
1) I have less "FELT" recoil and muzzle rise in my GP style AR's than the DI's. That is with MY rifles, not someone else's AR's.
2) DI ARs return hot gas, carbon and particulate matter to the receivers & BCG. The GP ARs return practically none. The return of this hot gas and carbon can have one of three effects to the receivers and BCG as compared to the GP. The hot gas and carbon can have a negative effect, a negligable effect or a positive effect.
Obviously the hot gas, carbon and particulates have a negative effect on the bolt, springs, the carrier, pretty much everything. It tends to gum-up-the-works. So yes the GP does show a "...marked improvement in reliability, durability." Marked being subjective, of course.
3) Accuracy? Debatable. NiCorr and Melonited coated bore in lieu of chrome makes for some discussion.
4) Complexity? Hardly complex. My 5 year old can take it apart.
6) Weight? What 4 - 6 ounces on a 7 pound rifle? Unnoticable.
7) Wear on the receiver extension. Older versions were problematic in that regard. Not so much lately. You have to go through thousands and thousands of rounds to begin to see if a problem exists.

Still a little fuzzy on the ski pole.bike thing though....
I agree with you on the M14 being a real-man's weapon.

 

[kfgk14]

Stay direct impingement, parts commonality and simplicity are paramount. Maintenance for a DI AR-15 is simple: Take slip2000/Hoppes/Synthetic motor oil/RemOil/other lubricant of choice. Apply to BCG and FCG. When necessary, repeat. If you're swapping in new parts/have down time, feel free to break it down and clean/degrease it, just remember to apply a film of lubricant after.

The piston adds other stresses and wear issues to the system, not to mention the important areas of the AR-15 already self-clean (go to vuurwapen blog and they'll show you in pictures better than I can explain).