Piston gas system AR-15?

[MatthewVanitas]

Not meant to copy the "HK M4 at SHOT" thread, but hoping to get info on piston gas (vice direct gas impingement) systems in the AR-15.

Are there any significant disadvantages to this modification? Does it seem reasonably practical?

Looking at the pic on HK's page for their piston-operated M4

http://www.hk-usa.com/pages/Military-LE/rifles-carbines/m4.html

It appears that the bolt is identical to a standard AR-15 bolt. Is that the case? Does the piston simply slide into the "key" of the bolt, where the gas usually flows?

It also mentions "refined lugs", would that be some improvement on the star chamber?

I find this concept very interesting. I was hoping to buy an Armalite AR-180B when I leave California, but if these turn out to be well received, I may have to turn back to the AR-15 side. I really like the ergonomics of the AR-15 system, especially the safety placement. I would also love to be able to use the wide variety of AR-15 aftermarket parts and spares. I still find the simple receiver and charging system of the AR-180B appealing, but a piston-op AR-15 is tempting.

I mentioned this system to another Marine and fellow gun-nut. His first reaction: "Dang, after we go and purchase a ton of M16-A4s, _then_ they bring out a piston rifle"

 

[Hkmp5sd]

You might have a long wait for one. They're not even going to be ready for the military/LEO market until the end of the year. But I'd like to have one to play with too.

 

[Jim K]

The AR-180 has other advantages over the AR-15 in that it is less susceptible to dirt and dust in the receiver (though the AR-180B is not as good in that respect, having no port cover), and is easier to take down. Plus, the stock can be used where it can get wet (as in a raft paddle) without tying up the gun.

Jim

 

[Jeff White]

There was the Rhino conversion kit back in the 80s. It wasn't a good seller. I have a friend who had one and never installed it. Next time I see him, I'll see if he still has it and try to get some details.....It's not a new idea.

Jeff

 

[MLC]

Regarding dust in the receiver:
If you look at some other pics of that upper there is no dustcover over the ejection port.
I think that they have modified the bolt and carrier to lessen the adverse effects of debris. The angle of ejection seems to be different based on the angle of the deflector.
I hope that we get a civvie version.

 

[Victor Romen]

By eliminating the gas impingement you can eliminate the gas relief holes that were located on the ejection port side of the bolt carrier. You could also eliminate the relief cut. In all it would make the bolt carrier heavier, but in theory more robust. I would say that you are right Matt about the piston sliding into the key. The key is probably solid. I wonder if that would put stress on the key though as it was not designed to be hit by a fast moving metal rod.

 

[Bartholomew Roberts]

"Refined lugs" probably just means they radiused the lugs on the bolt since bolt lugs breaking or cracking is a known weak-point of the current AR15 bolt. All of the SOPMOD Block II submissions for an Improved Bolt program outlined in 2001 also use radiused lugs.

 

[Kharn]

According to the discussion on www.hkpro.com, The gas key in the HK system is solid, not hollow like the current one. The piston contacts the solid front of the gas key to drive it rearwards.

So far, the new parts count appears to be:
New carrier key
relief-less carrier (required?)
Ejection-port-less upper (required?)
Piston
Return Spring (?)
front sight base
Modified handguard (?)
New buffer (required?)

A retrofit kit for $~200 (if a new carrier (refit old carrier with new gas key) and upper arent required) would be pretty cool.

Kharn

 

[QuarterBoreGunner]

I posted this in the 'HK M4 at SHOT' thread;

It looks almost like a modified FAL gas system... now if they could introduce a gas adjustment device in the front of the sight tower....mmmh on second thought maybe not.

 

[ks_shooter]

One benefits of the AR-15 gas system is that the expanding gas in the bolt carrier pushes both forward and backward. As the gas expands, the pressure pushes the bolt carrier backwards, starting the recoil cycle. It also forces the bolt forward. This reduces the pressure between the locking lugs on the bolt and the barrel extension while the bolt is rotating during the unlocking process. The alteration to the locking lugs may be necessary to address this change.

 

[Quack]

KKF is working on his own short piston AR.

 

[Gabe]

Now what we need is one in 308, 5.45, 7.62x39, 6.8SPC, 6.5Grendel. . .

 

[uglygun]

It also forces the bolt forward. This reduces the pressure between the locking lugs on the bolt and the barrel extension while the bolt is rotating during the unlocking process. The alteration to the locking lugs may be necessary to address this change.

Very observant.... How many times have we seen the ejector gouges on brass from where the force of the bolt driving into the base of the cartridge has left an obvious mark in softer brass?


It would be VERY interesting to see if the HK upper up close, see how those bolt lugs may have been changed. Also, to inspect the brass to see how it marks the brass upon extraction compared to a typical AR15/M16 action.

 

[Quack]

close up pic of the gas piston

 

[WonderNine]

Now let us pray that HK sets up a factory here....

 

[skebe]

Orrrrrrrrrrrr,

You guys could ask Kurt of KKF (Kurts Kustom Firearms) if you could buy his ar15 gas piston system.

KKF

"Pictured above is the new KKF M9EvoM4 , This new gas system for the M16/M4/AR15 family of weapons increases reliability, runs cleaner with no barrel gasses bled back into the action, and runs smoother. Karbine and Mid-length systems, and tuned uppers available 04/2004. "

"Internally the XM8 employs a combat-proven robust rotary locking bolt system that functions and fieldstrips like that used in the current M16 rifle and M4 carbine. However this bolt is powered by a unique gas operating system that employs a user removable gas piston and pusher rod to operate the mechanism. Unlike the current M4/M16 direct gas system with gas tube, the XM8 gas system does not introduce propellant gases and the associated carbon fouling back into the weapon’s receiver during firing. This greatly increases the reliability of the XM8 while at same time reducing operator cleaning time by as much as 70%. This system also allows the weapon to fire more than 15,000 rounds without lubrication or cleaning in even the worst operational environments."

New KKF Gas System Works! thread

 

[Badger Arms]

I'll put in another vote for the KKF system. Biggest benefit of Kurt's: You spend about 10% of the cost and he just modifies YOUR gun. Looks exactly the same... no new upper, no new bolt carrier, and.... oh, BTW, HK doesn't plan on marketing this to civies!

For those of you who MIGHT think this is new, Colt modified a gun to offer to the US Army decades ago: