The Firearm Blog

Stag Arms's newest AR-15 is the piston operated Model 8 carbine.

Model 8 Piston Carbine

Stag have not released much information about the rifle. It looks much the same as their M4-style Model 3 carbine. I am not sure if the piston system is their own design (if you can identify, please do in the comments). It looks like it could be a long-stroke design, but I am not sure. UPDATE: See below.

Piston system can be seen when upper handguard is removed.

Lefties will be pleased to see that a left-handed model will be available.

UPDATE: David from Stag told me that it is a short-stroke piston that Stag Arms designed.

Murdoc has written a review of the Adam Arms retrofit piston system for the AR-15 for Guns and Hunting.

The new Adams Arms gas block quickly mounted with hex screws and a new bolt carrier key, a couple springs and a bushing were all that was needed before adding the sleeved drive rod. Supplied front handguards mounted normally, and I was left going back over the installation manual, convinced that I must have missed something. It was that easy. Though it took me more than half an hour due to the troublesome factory gas block, this is certainly a task that can be accomplished by a moderately capable gun owner.

It is a well written review and worth reading.

This 3D animation shows how the piston system works verses the AR-15’s normal method of operation, direct gas impingement.

This year Smith & Wesson have launched the M&P15 PS and PSX piston operated AR-15 rifles.

M&P15 PSX

The only difference between the PSX and PS is that the PSX features a Troy 7″ modular quad rail handguard.

M&P15 PS model and Piston Operating System
Photo ⓒ Remigiusz Wilk (REMOV). Used with permission.

Specs:

Barrel Length: 16″
Barrel Twist: 1 in 9″
Overall Length: 35″ Extended/32″ Collapsed
Stock: Collapsible 6-position
Weight: 6.5 lbs.
Finish: Hard Coat Black Anodized

I do not know the MSRP on either model.

This video clip is from a marketing video made by H&K comparing the 10″ barreled HK 416 with the M4 when fired full of water, immediately after being submerged.

It is a pointless comparison. Obviously Stoner did not design the AR-15 platform to be fired waterlogged. If he had it would be piston driven. Still, it is interesting to see what happens.

H/T: MP.net

Over the past few months Colt has been unveiling a variety of new AR-15 firearms. If a replacement for the M16 or M4 is chosen they want it to be a Colt. To ensure this designed a range of weapons that should cover all bases. David @ Defense Review has been relentlessly covering the new firearms.

Many of the improvements Colt have developed have been applied to all these guns, I won’t list them all, click the links to read the full details.

Colt Sub-Compact Weapon (SCW)

A 5.56mm 10.3″ barreled sub-carbine/PDW featuring the new Colt side-folding stock. It is able to use an upgraded gas impingement system or the Colt Piston System (CPS)

Side Folding Stock. Photo by SMGLee.

Colt ACC-M (Advanced Colt Carbine-Monolithic)

This is basically an upgraded M4. It features many small improvements over the M4A1 and Colt’s new monolithic rail system. If it was adopted it I think it would probably be named the M4A2.

Colt Advanced Piston Carbine (APC)

David calls this the HK416 killer. It utilizes the Colt Articulating-Link Piston (ALP) system.

Colt Advanced Hybrid Carbine (AHC)

This carbine features a hybrid gas impingement and gas piston system. I am very interested to see how that works.

Colt Infantry Automatic Rifle (IAR)

I covered this a few weeks ago on the blog. It is a light machine gun and Colt’s entry into the Marine Infantry Automatic Rifle competition.

Colt IAR. Photo by SMGLee

Jennersen was kind enough to photograph his Bushmaster A3M4 Gas Piston system for me. He took some really good shots.

Thanks Jennersen!

The rest of them are here.

The POF-USA P-308 is a interesting rifle. It is a gas piston operated rifle, based on the AR-10/AR-15 design and requires no lubrication.

14.5″ version

They achieve this by plating the upper receiver with silicon nickel and chroming and heat treating the bolt and carrier.

Upper receiver

Here is a video of it in action

In spite of its name, it is chambered in 7.62X51mm, not .308 (yes, there is a difference).

More info at POF-USA and Defense Review.