The new Colt 6940.

[icm856]

Anyone see this one yet? It's Colts new LEO carbine. It has a 1 piece monolithic upper receiver with a full length free float rail, flip up front sight gas block and a 600 meter rear flip up combat sight. It looks sweet!

[LurpyGeek]

Haven't seen much info about it, but what I've seen seems to say it is direct impingement like a standard AR.

You can get a similar carbine with a monolithic upper and a piston operating system for much less $$$ as well.

[icm856]

Originally Posted by LurpyGeek

Haven't seen much info about it, but what I've seen seems to say it is direct impingement like a standard AR.

You can get a similar carbine with a monolithic upper and a piston operating system for much less $$$ as well.

Yes, it is a "DI" I have 2 POF gas piston AR's and they are great guns, however I have about a dozen DI AR's as well and find them to be just as reliable. The Gas Piston AR is not the best thing sense sliced bread and this is why not every AR manufacturer has jump on the Gas Piston ban wagon. Below is part of an article by C. Reed Knight that takes a closer look at both systems.


He makes a pretty good argument for why the AR platform is not suitable for a gas piston system and
should be kept as a direct impingement gas system.




Mr. Knight wrote

With the direct gas impingement system, when gas goes through the gas tube and into the bolt carrier via the snorkel, the gas pressure forces the bolt FORWARD, holding it
securely in place, locked in the barrel extension, while the pressure behind the gas rings forces the bolt carrier backwards. The bolt is pushed forwards by gas, and the bolt
carrier is pushed backwards by gas. The cam action rotates the bolt out of battery and the inertia imparted to the bolt carrier pulls the bolt out of the barrel extension.
The pressure applied on the carrier is almost entirely aligned with the direction of travel of the carrier. The carrier gets pushed straight back, excluding some relatively
minor torqueing forces applied via the gas stream through the snorkel. The carrier action is very linear, without any significant lateral forces applied to the upper receiver
or carrier.


With a gas piston system, there is no supplemental pressure burst against the rear of the bolt to hold it securely in battery while the pressure curve drops off, which may or
may not be significant, but more importantly, the driving impulse on the bolt carrier is off -axis by a respectable amount, well outside the outer diameter of the carrier, which
makes the carrier torque toward the bottom of the upper receiver, causing rapid premature wear, and in some cases, a minor misalignment between the upper receiver bore
and the buffer tube bore can become a point at which the bolt, being driven back with a considerable downward torque force on its rear edge, snags and takes some damage
with every shot. Bolt carriers that are used in piston guns should have beefed up bearing surfaces on the lower section of them and the lower rear of the carrier should be
given a good, well polished ramp cut.

Knight also says that bolt breakage is considerably higher in piston ARs than in direct impingment ARs. The reason is apparently due to the very sudden impact delivered to
the bolt and carrier by the gas piston when driven by the gas stream, compared to a more moderate push given to those parts by a direct impingement gas system which
has a definite pressure curve profile to it, much different from the virtually "square wave" pressure curve delivered via a piston system.

[LurpyGeek]

Originally Posted by icm856

The Gas Piston AR is not the best thing sense sliced bread and this is why not every AR manufacturer has jump on the Gas Piston ban wagon. Below is part of an article by C. Reed Knight that takes a closer look at both systems.


He makes a pretty good argument for why the AR platform is not suitable for a gas piston system and
should be kept as a direct impingement gas system...

I wasn't advocating the piston system on ARs and I wasn't saying that direct impingement is a terrible thing either. I was just saying that there are better things out there.

I have a Robinson Armaments XCR. It has a monolithic upper receiver, integral quad rail, adjustable piston and excellent ergonomics. The three-lug bolt is much beefier than a standard AR bolt. I purchased it for about half of what I've seen the new Colt carbine listed at. I'm not bragging, I'm not saying it's the best thing out there, or that it's better than anything anyone else has, but I've been extremely happy with it. Sorry if I sounded snarky.

[icm856]

Originally Posted by LurpyGeek

Sorry if I sounded snarky.

No offense taken Sir, I appreciate your response.