Gas Tube Blues

[LRRPF52]

i thought i read a long time ago, that the ball powder being used in 223 ammo in Vietnam had a high calcium carbonate content. i guess that is a flash suppressor?? not sure, any way i heard antidotal stories that the calcium carbonate would plate out in the gas tube and eventually cause failures to cycle due to plugging up the gas tube. when they went to different powder the problem went away. i also read somewhere that Eugene Stoner intended the gas system design to use cartridges with stick powder, not ball powder for that reason. Since the AR gas system issues have been well sorted out now, in the almost 60 years since the AR's adoption, i wouldn't expect stoppages due to plugged up gas tubes anymore. in line with the OP question, i am curious if anyone has recently ended up with failures to cycle due to not cleaning out the carbon in either the gas tube or the bolt carrier expansion chamber? other than liking things clean, has it ever caused a malfunction? i haven't used my first build much, since i haven't had a lot of time off of work, but i also haven't yet cleaned the gas tube or the BCG expansion chamber. and if i don't have to, for functional reliability, i may not bother. on the other hand if not cleaning these out does indeed cause malfunctions down the road, then i'll have to put it on a maintenance schedule at x number of rounds.
thanks,
-tdbru

It is true that the AR15 was engineered around small stick powders, one of which was 8208M at the time.

However, the problems experienced early with the AR15's fielding in Vietnam were a result of several things:

* The Colt Model 602 AR15 was mass-produced with reamer variances that ranged from satisfactory to way too tight of chambers, while the first Model 601 guns were fine (The Green Rifle).
* The chamber was not hard come-plated.
* Cleaning kits were not specified or issued to soldiers.
* The new lots of ammunition were loaded with ball propellant, instead of stick powder because they had a hard time maintaining consistent burn rates with the tiny sick powders in extreme high volume production for the Army and USMC demand. Rifles were tested and benchmarked for production spec sign-off by DoD using the known-performer stick powder ammo, then sent to Vietnam and fed the unknown, ball propellant ammo. Gas port pressures with the ball propellant ammo increased to well over 10,000psi, far outside of the timing window for the cycle of operation.
* The humid tropical climate of Vietnam caused quick chamber erosion.



Combine a tight chamber, corroded/rough-textured chamber, with no cleaning kits/limited lubrication, and extreme high port pressures and you get Failure To Extract all day long, regardless of what design the rifle is. Those RO602 AR15s would FTEx, including case head separation, with no broken shell extractors issued, let alone cleaning kits with bore and chamber brushes.

There were 2 USMC officers or senior NCOs that wrote letters back to their Congressmen telling them about how the AR15 was getting guys killed, how they were scrounging for enemy weapons to issue out, costing them their careers. Congress held hearings on it with the Ichord Subcommittee, and found out a lot of the dirty laundry of how the program was mismanaged.

The result largely entailed things the Army was already working on, but manifest all the corrections with the Colt Model 603, otherwise known as the M16A1.

The best features that corrected the problems were:

* Hard Chrome chamber and later bore
* Maintain spec on the chamber reamers so that you don't go below minimum chamber
* Addition of the heavier buffer, replacing the Edgewater Spring Guide
* Issue of cleaning kits with sectional rod, bore brushes, and M16-specific chamber brush, with oil bottles



The unnecessary and retarded feature they added that Stoner recommended against and the USAF refused to adopt for their rifles was the Forward Assist Assembly. The Army had an infatuation with the Forward Assist, thinking that it was the panacea of helping chamber rounds that didn't want to be chambered. In reality, a lubed M16A1 ran like a raped ape and never needed Forward Assist, but it made some engineers in the Army Ordnance Board feel warm and fuzzy inside, so it became standard.

The USAF got their own rifle nomenclature and Model as a result, separate from the Army, with the Colt RO604. USAF Special Operations personnel used slick side Carbines as well, and the Son Tay Special Forces Raiders used the USAF GAU-5A/A carbines for their extensive training and execution of the Son Tay Raid in 1970.

Anyway, I've shot insane amounts of 5.56 NATO and 6.5 Grendel over the years, as well as 7.62 NATO and .260 Rem through gas guns. I've never cleaned a gas tube inside other than to hide some of the carbon residue near the end of the tube with pipe cleaners before ORS inspections in the Army, and the only reason for that was to pass the monstrously-stupid white-glove inspections where all the CLP was stripped of the weapons to make them bone-dry so that senior leaders with zero understanding of weapons maintenance and basic materials science can be happy with the cleanliness (and lack of functionality) of the weapons in their assigned inventories.

The TMs specifically forbid the insertion of Q-tips into the gas tube, as soldiers subjected to white glove inspections have clogged their gas tubes with little compressed cotton balls that way, which will turn the rifle into a single shot.