Why direct impingement?

One advantage is not having the piston slamming back and forth above the barrel, reducing barrel harmonics. I like the easier cleaning that comes with a gas piston design though.
 
It also eliminates a lot of momentum and action above the barrel and instead puts all of the movement and inertia of recoil in a straight line behind the barrel, keeping the recoil horizontal and not vertical...thereby reducing muzzle climb
 
Stoner wasn't the only designer working with 'direct impingement' gas systems, which could be described as 'open gas tube'. The French MAS 1940, MAS 1944 and MAS 1949 used this simple principle, and others will post their examples. Gas is bled off the barrel, gas goes backwards and expands in a chamber on the breech block carrier. In my opinion, Stoner used it because it is remarkably simple and has no awkward gas plugs, rods or springs (M1 Garand, SVT40 and G43). He was nobody's fool.
 
I don't believe it was ever intended as a design feature, but they are inherently more accurate than one that is piston driven.
 
Strictly speaking, the gas system used in the AG42 and MAS use direct gas impingement. The AR series do not. In the former, gas is piped back, and makes direct contact with the carrier in a little socket, blows the carrier back. In the AR, gas is ducted into an expansion chamber within the bolt carrier; the expanding gas forces the carrier and bolthead apart. This movement imparts rearward energy to the carrier, and rotates the head to unlock. It is also the reason that the AR bolt heads have piston rings. The AR system is a lot more sophisticated than the AG/MAS.
 
peckerwood said:
It also eliminates a lot of momentum and action above the barrel and instead puts all of the movement and inertia of recoil in a straight line behind the barrel, keeping the recoil horizontal and not vertical...thereby reducing muzzle climb
Click to expand...

I think you have to have actually shot both DI and piston to be able to compare.



As far as the DI goes I squeezed off a few hundred rounds in a full auto M16 down in the states and while recoil was surprisingly manageable the muzzle climb was a lot more dramatic than I expected with the M16 being what it is (and for comparison's sake I've fired more than a couple FA toys here and there)...


I think muzzle climb is just something that's simply unavoidable and while DI might reduce it to a degree I didn't notice anything spectacular. I guess the plane of muzzle climb was more slanted in an up and to the right pattern though.
 
Last edited:
The fact that my Father is an American citizen with property in California, Arizona, Wyoming, Nevada, and Colorado lends one the ability to have a visit and fire some interesting weapons...the M16 included.

And yes I have fired selective-fire piston driven 223 rifles and they have always seemed to have more muzzle climb than that of the M16 variants for the same length of barrel. While it is a minor amount of muzzle climb difference, it is seemingly more noticeable in FA.
 
My guess is that Stoner chose DI primarily for weight reduction purposes. While it is probably true that piston-driven rifles have more muzzle climb (all else being equal), I doubt that the difference is all that dramatic. Likewise, I don't think that having fewer parts was an important consideration. The AR is hardly a simple design, especially compared to guns like AK-47.

On the other hand, the AR-10 was essentially a study in using lightweight materials. Armalite was founded as a division of Fairchild Engine and Airplane Corporation with the specific purpose of designing lightweight weapons. Early AR-10 prototypes even had aluminum barrels (which burst during military trials). So it seems like Stoner had a mandate to build the lightest rifle possible at the time and reliability was a secondary consideration.
 
You must log in or register to reply here.
Back
Top Bottom