Best AR-15 Gas Piston conversion kit

**.cheese.** · February 8th, 2009, 01:20 AM

??? What is it?

**symr00** · February 8th, 2009, 10:56 AM

**.cheese.** · February 8th, 2009, 12:43 PM

huh? They don't seem to sell a conversion kit... just complete rifles.

**gvnwst** · February 8th, 2009, 02:31 PM

I think they stopped, i checked their site a few weeks ago, and i couldn't find then either. before that, they did have a link.

Are you fixated on a conversion kit, or can you buy a complete rifle? Bushmaster makes the most popular conversion kit, and POF-USA makes the best piston ARs, period.

**HorseSoldier** · February 8th, 2009, 02:39 PM

You're probably better off just getting a piston upper, rather than a conversion kit.

**.cheese.** · February 8th, 2009, 03:37 PM

I would rather not waste my current uppers by replacing them. I'd rather just convert them.

I am buying 2 piston ARs complete (Sig 556 SWATS). I would also like to convert my current LMT ARs to piston operation.

**Sheik Yerbouti** · February 8th, 2009, 05:43 PM

The best ones don't use AR15/M16 bolt carriers, and consequently don't use standard uppers. With the lack of rails for the carrier to ride on and the offset torque of the piston pushing a modified key, many people are finding that piston conversion cause accelerated wear, I mean, really accelerated wear on the uppers.

If you want a piston driven autoloader, get one that was designed that way from the ground up, like the Sig 55x or the AR180.

**HorseSoldier** · February 8th, 2009, 07:31 PM

The ADC PD15 has some modifications to address the wear and tear issue, as do (I think) some other models, but again it's not a conversion kit, it's a dedicated build.

**PercyShelley** · February 8th, 2009, 07:33 PM

I suppose it's rather remarkable that you can take a standard AR upper, bolt carrier and barrel, and tuck a piston in there and somehow have it work.

**rangerruck** · February 8th, 2009, 08:13 PM

osprey defense industries, if they still do it...

**Fly320s** · February 8th, 2009, 09:06 PM

A friend has had good results with his Adams Arms piston coversion.

**.cheese.** · February 8th, 2009, 09:48 PM

go further in explaining the problems with converting an AR-15 to gas piston operation please so I better understand the issue.

**Sheik Yerbouti** · February 9th, 2009, 01:27 PM

Carrier tilt causing uneven wear on the interior of the upper reciever.

Uneven load on locking lugs causing unnatural bolt wear.

Carrier key shearing.

If you dig through all the marketing hype (and these things are selling like hotcakes), you can find some of the horror stories. They tend to crop up with people who shoot a lot, not your casual one weekend-a-month shooter. Basically, things break rather quickly that normally don't in an unmodified system. If it ain't broke, don't fix it. YMMV.

**PercyShelley** · February 11th, 2009, 01:01 PM

I've seen what carrier tilt can do to receiver extensions, and I've seen shorn gas keys (although those can happen with DI too if the key isn't staked and it's a heavy enough firing cycle and the Joon is in the second house and Jupiter aligns, etc), but I'm curious as to how the locking lugs could be affected by a gas piston conversion.

**Wild Deuce** · February 11th, 2009, 01:28 PM

I would be interested in hearing more of these stories and getting more details. What axis are you referring to when you say carrier tilt? longitudinal or lateral?

I had a PWS conversion installed on mine and have not had a problem but like it was mentioned earlier, I don't shoot that often. Maybe one to two hundred rounds a month.

**ChopMeat** · February 11th, 2009, 11:25 PM

I did my Bushmaster with their kit, I like it. It was pricey though $400 + shipping. I like it and have not seen any unusual wear and tear. I didn't have problems with it before. I just thought it was a good idea to make it similar to my AKs actions. I noticed a little less cleaning in the receiver since the conversion. The gases vent downunder the handguard. (I feel it sometimes, but it doesn't bother me.) I wish they vented out before the gas block instead. Oh well, I want to do my Rock River next.

**PercyShelley** · February 12th, 2009, 01:33 AM

WildDeuce, most typically the carrier pitches, nose up and the back end of it digs into the receiver extension. Since the carrier is steel and the buffer tube is aluminum, this can muck it up pretty good after time.

Most piston conversion or upper manufacturers seem to acknowledge that this is a problem in all the other companies' products. I have no idea how prevalent or severe it typically is, or even on a per-brand basis, just that it is possible.

**Regolith** · February 12th, 2009, 03:49 AM

Percy....is that just just an issue with conversion kits, or is it a problem with all piston AR's, including those designed for it from the factory?

**PercyShelley** · February 12th, 2009, 06:14 AM

I don't know that either. I suspect that the problem could occur in either, since it's caused by the strike from the piston having some moment arm on the raised gas key relative to the center of the bolt carrier. On some purpose-built gas-piston bolt carriers, like the one in the HK 416, the key is moved back a bit, probably to reduce this problem.

**Wild Deuce** · February 12th, 2009, 12:32 PM

Hmmm ... wouldn't the moment arm be the same regardless of how the energy is delivered (gas impingement or piston stroke)? How about my PWS system that has a long carrier key fitted inside a piston tube? Shouldn't that prevent or minimize any pitching of the bolt carrier?

Just wondering ... I'm not an engineer. Thanks for the information. I will definitely keep an eye out for any unusual wear.

**Wild Deuce** · February 12th, 2009, 01:20 PM

I'm answering my own question here ...

This seems like a reasonable and logical response to my inquiry about the moment arm being similar. (from another forum)

Whether the BCA gets shoved back by a piston or a blast of hot dirty air, it gets hit in the same place with the same force. I'm guessing this is urban legand, but I'll look into it. I jut doubt very seriously the uppers had to be 're-engineered' to accommodate the pistons. Oly did this years ago with their 10mm conversion uppers. They used a Rhino piston system.

I might be wrong here, but technically the BCA is not "blown back" by the gasses acting on the key. The gasses are directed by the key into the BCA where they push the bolt forward and the carrier rearward. So, theoretically, the pushing force is centered within the BCA (which is what Stoner wanted).

Edit: Here's a quote from http://www.lwrifles.com/content/LWRC.pdf:
"One of the issues associated with a piston is that kinetic energy is applied to the bolt carrier off axis. That means the steel carrier could tilt and wear on the aluminum receiver. LWRC uses a proprietary bolt carrier (but standard bolt) in which a special carrier key is used. To prevent carrier tilt, LWRC has designed a slight downward angle on the carrier key—toward the operating rod to re-vector the delivered kinetic energy to the carrier so that it moves straight back in the receiver instead of tilting. The carrier is also stabilized by a boss of increased diameter on its back."

I don't know how well this works, but Leitner-Wise has been in the skunk works business for a while and they have made several improvements to the original AR design (such as bolts and extractor claws). Will other companies put as much into making sure that their carriers don't have this problem? Who knows. Unless the zombies start coming, I'll stick to cooking with gas (it hasn't let me down yet).

Regarding carrier tilt, it seems that someone is on to a "cure" for this malady. If anyone has any more info or data on this, I'm all ears.

**gvnwst** · February 12th, 2009, 08:37 PM

Regarding carrier tilt, it seems that someone is on to a "cure" for this malady. If anyone has any more info or data on this, I'm all ears.

I too am intrested, and so posted there asking if he has any updates. If there are, i will copy them to here.

**PercyShelley** · February 13th, 2009, 02:07 AM

Hmmm ... wouldn't the moment arm be the same regardless of how the energy is delivered (gas impingement or piston stroke)? How about my PWS system that has a long carrier key fitted inside a piston tube? Shouldn't that prevent or minimize any pitching of the bolt carrier?

Just wondering ... I'm not an engineer. Thanks for the information. I will definitely keep an eye out for any unusual wear.

I thought exactly the same thing when I first heard this, and I'm not an engineer either.

Since I've seen pictures of lower receivers and buffer tubes all banged up by the back of the carrier, though, I think there is actually something to this.

Incidentally, in the purpose-designed piston system of the AR-18, the piston strikes the carrier between the two guide rods that the carrier rides on. I wonder how much the bolt carrier of an AK gets torqued during operation?

**Sheik Yerbouti** · February 13th, 2009, 07:32 AM

I wonder how much the bolt carrier of an AK gets torqued during operation?

It doesn't matter since the AK carrier rides on rails.

**gvnwst** · February 13th, 2009, 09:46 AM

Hmmm ... wouldn't the moment arm be the same regardless of how the energy is delivered (gas impingement or piston stroke)? How about my PWS system that has a long carrier key fitted inside a piston tube? Shouldn't that prevent or minimize any pitching of the bolt carrier?

Just wondering ... I'm not an engineer. Thanks for the information. I will definitely keep an eye out for any unusual wear.

I thought exactly the same thing when I first heard this, and I'm not an engineer either.

It would not do much different, the offset is still there. My POF uses a ling connecting rod, that could, in theory, be attached to the BCG, if it was, would it be any different? Well, the only difference i can think of is that there will be two "rods" riding surfaces, and so part of the tourque will be put onto that extansion.

It doesn't matter since the AK carrier rides on rails.

So, if a BCG rides on some sort of AK style system, you will have "none" of these problems? Hmm....anyone else thinking some kind of AR upper that is REALLY a AR/AK crossover?

Basically a AK upper, all the same pars, bolt (will that work with AR mags?) bolt carrier, gas tube/system, ect.... Just need to find a way to get the shorter BC to wirk in a AR type upper...

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