07-27-2011, 10:08 PM
bwaites Wrote:As I understand it, barrels are not the issue with sustained fire, gas tubes are. There is a very good video online demonstrating what happens to an AR with prolonged auto firing, and the gas tube is destroyed first, leaving the shooter with essentially a straight pull bolt action rifle.
So I simply don't think that adding a better/heavier barrel will solve the issue, the weak link appears to be the gas tube, not the barrel. It may be true that repeated auto fire that approaches but does not cause gas tube failure might cause the barrel to become progressively damaged, decreasing accuracy, but any M4/M16 variant being used that way isn't going to be used as a long range sniper rifle anyways!
I watched one of my Team Leaders melt a SAW barrel one night firing excessive string after string of rapid fire without changing barrels. Through NODs, you could clearly see the fore end of the barrel start to slowly bend downwards, ever so slightly. The SAW barrel has twice the chrome lining thickness of an M16, and is of machinegun-rated steel designed for full auto high volume. I do agree that heavier barrels are not the answer to addressing this limited problem with the M4 that was encountered by Joes in COPs set up for failure.
They're trying to address barrel influence by the RAS, dynamic tension on the handguard, and accessory mass influencing POI shift with a heavier barrel, when free-float is the real answer. Free-float also is the best thing you can do for heat dissipation, as SF and other SOCOM units have been doing with the RIS II.
When we talk about heat transfer in a weapon under unusually high volumes of fire, there will have to be a compromise somewhere else. AK's have failures in the op rod assembly, handguards catch fire, parts break, etc. Barrels melt and gas system parts will exceed design limitations somewhere in all the designs I know of. This is why the FAMAS and L85 can't reliably shoot standard M855 ammunition, and run on much lower-pressure cartridges. I think the French even use steel cases in the FAMAS since it will blow brass cases apart.
Op-rods on M14's break, gas pistons become fused in the block with excessive heating and cooling, and HK's will warp the stamped receivers under extreme high-volume, even in an MP5. Extreme heat is extreme heat at the end of the day. Combine that with extreme hot or cold climates, and the material expansion/contraction characteristics exceed design limitations quickly. If one were to attempt to solve this challenge by using an op-rod system, the problem just gets relocated and exposed to more environmental debris in the process, making failures under normal conditions more likely, a la HK416.
The one area I do see the Grendel offering an advantage in the heating challenges is that it operates at significantly lower pressures than 5.56 NATO, 6.8 SPC, and 7.62 NATO. An 85-100gr assault rifle load would also have comparable recoil characteristics to 5.56 NATO, as I have seen in my own 100gr Nosler Ballistic Tip loads with 29gr-31gr of TAC.