Researchers at the Naval Surface Warfare Center Crane Division — NSWC-Crane — are putting a long-running debate to rest. Is the standard carbine-length gas system the best? Or is there an advantage to mid-length?
Specifically, the testers wanted to see if the mid-length gas system showed significant advantages with shorter 14.5-inch barrels. But these findings apply as much as, or more for, 16-inch barrels which are the most common on AR-15 rifles today.
The carbine-length gas system was designed to cycle a wide range of barrel lengths and profiles. Even though it’s a standard many companies and shooters alike disagree, leaning toward mid-length.
In recent years boutique builders and prominent manufacturers started using the mid-length gas system, not just on 16-inch carbines, but also 14.5- and 14.7-inch setups.
The supposed benefits of the mid-length setup include lower running temps, shorter dwell times and less gas pressure on the system. The potential drawback is lower reliability — after all, it’s not the norm.
But because the carbine-length gas system is capable of cycling guns with barrels starting around 10 inches, it shows signs of over-gassing guns with longer barrels. Many users turn to extra-strong buffer springs, heavy buffers and enhanced bolt carriers to improve performance with their carbine-length gas systems.
NSWC-Crane started a series of tests to determine what the actual benefits and drawbacks of using mid-length gas systems with 14.5-inch barrels. And while they haven’t published all the results, initial tests confirm what a lot of shooters have been saying.
Mid-length looks a lot better with 14.5-inch barrels. Again, these results also carry over to 14.7- and 16-inch barrel rifles.
NSWC-Crane tested for overall reliability, high- and low-temperature reliability, accuracy, projectile velocity and cyclic rate. They also performed tests suppressed as well as unsuppressed.
In most cases, the mid-length gas system outperformed the carbine-length system. The mid-length system matched or bested the carbine-length system in terms of muzzle and terminal velocities, cycled more slowly — slower is better in this case — and the mid-length system had far fewer malfunctions.
All of the testing used the new M855A1 Enhanced Performance Round. This is very high-pressure ammunition and is considered a “barrel burner” since it puts a lot of wear on rifles.
While it was nice to find that the mid-length system malfunctioned half as much as the carbine-length system, NSWC-Crane’s real eye-opening finding was that the mid-length gas system showed a far better service life than the carbine.
Crane researchers started to see a degradation in accuracy and performance at around 6,000 rounds with their carbine-length setup. But they saw no drop in accuracy with their mid-length setup even after over 12,000 rounds.
So is there any benefit to carbine-length gas systems on 14.5-inch barrels and longer? Looking at these results, the answer is not generally.
Obviously the carbine-length gas system is still useful for shorter barrels, and it’s useful for other cartridges and loads. But for full-house 5.56 carbines, mid-length appears the way to go.