M-4 to Get Pistons

This is great news and an amusing headline.

My own title looks like nonsense to anyone who isn’t into guns, I suspect.  For those who don’t know what it means, there have been complaints about the reliability of the M-4, the current derivative of the venerable M-16 assault rifle.  Most of the complaints have to do with the way the action works, being a direct gas system. 

For the layman, direct gas systems take the expanding propellant gases from each round fired to push the bolt back and load another round. Direct is what it sounds like; the gases go straight back into the receiver.  That means a lot of gunpowder fouling of the receiver which is the most important part of the weapon.  The more fouling the easier it is to jam in the middle of a firefight.

A piston system siphons off the expanding gases into a separate chamber where they push a piston that in turn moves a rod that transfers the energy to the bolt.  That keeps the bulk of gunpowder residue up in the piston area where there are fewer moving parts.  With a cleaner receiver there are far fewer jams, as the article shows.

There are complaints that short piston equipped M-16/AR-15 rifles are front heavy and the M-4 was designed to be light and compact.  But a weapon that is more reliable while keeping all the other good traits is worth the trade off, I think. If I had the money, I’d get a piston AR-15 rather than the classic design.  But I like front heavy rifles and heavy rifles period.

This modification is something I’d hoped the Army would do years ago.