Piston -vs- DGI systems test in SAR
Interesting article in the March SAR issue. They ran 1,000 rds through a piston upper and a std direct gas impingement upper. They did 100 rd Beta C mag dumps, full auto, reloading as fast as possible. The results were interesting. The piston upper ran like a striped ape and showed no signs of slowing down. The std upper puked after 264 rds. It had a "gas tube failure", which I take to mean it melted down and sprang a leak somewhere, as it no longer had sufficient back pressure to cycle the bolt.
Temp readings were taken at several locations. The bolt face on the piston upper reached 122 deg F after 1,036 rds. The DGI upper reached a peak of 133 deg F after 264 rds. The chamber temp of the piston gun reached 131 deg F after 1,036 rds. The DGI gun reached 115 deg F after 264 rds. The gas block temps were interesting. The piston upper reached 498 deg F after 200 rds and peaked at 697 deg F after 1, 036 rds. The DGI upper hit 339 deg F after 200 rds.
So the piston upper was found to transfer heat at a much slower rate than a direct gas impingement system. Big duh there. But the interesting thing is the gas block heats up much hotter because the gas is stopping there. The gas block is taking one for the team by absorbing a tremendous amount of heat, as the piston and op rod continue, without the gas, to cycle the bolt. But even at twice the temp of the normal gas block, the piston upper ran like a champ.
So what does this all tell us? The most striking thing that I see out of it is: to run repeated full auto mag dumps like a SOF team doing an IA drill, a piston upper is very desirable. If this very heavy firing schedule is you idea of a good time, a piston upper might be a good idea.
With a std, direct gas impingement system, it would be wise to limit full auto mag dumps to 5-6 30-rd mags. Yeah I know they did it in "Heat", and yeah it looked really awesome, but you will probably damage your weapon doing it.
What about semi-auto fire? I would be interested in seeing what kind of schedule would be equivalent to around 264 rds of full auto fire. I have cranked out over 1200 rds in a 8 hr period in a carbine course, and I never noticed my gas tube glow cherry red, as it did in this test. I would have to assume if a carbine can stick to this kind of schedule, then you will probably be OK in most any tactical situation.
The only time I ever stopped a carbine was was in training, doing a break contact drill, where I went through approx 200 rds of blanks, full auto, which carboned up the reciever so bad, the bolt stuck in the locking lugs. The gas tube was cherry red and the handguards melted down at the front corners.
So while I'm not a big fan of the piston uppers, as yet, I do see their uses for the extreme upper limit of the envelope. They may be the answer to SOF's problems with the M-4.
Working for Crossfire Australia, a military rucksack and load-bearing equipment company. Still doing limited design and development of nylon LBE.
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