UMC Blackout

[LouBoyd]

My first suggestion would be to use even heavier bullets. It takes more pressure to drive a 220 SMK than a 200 SMK to the same velocity. There are no doubt even heavier bullets no longer than the 220 SMK though with a lower BC. Remember the impulse to drive the bolt carrier only comes from the time the bullet passes the gas port until it exits the barrel. With a 7.5" barrel and a 4.7" gas port that's only 2.8" of barrel where the gas can exit the port. At 1000 fps that's only 233 microseconds that the propellant can feed into gas system. That's damn little. You could shorten the position of the gas port by and inch or more but keep the gas tube length long by folding or wrapping it around the barrel. That's easier (at least cheaper) than buying a new barrel.

The gas pickoff for a Desert Eagle is only about 1/8" from the case mouth but the "gas tube" runs the length of the barrel to drive a piston at the front. It's a requirement that enough ENERGY is put into the gas system to operate the mechanism. Energy is pressure multiplied by time. If you don't have enough energy to drive the bolt carrrier you have to either increase the pressure or time the of the gas that's applied through the bolt carrier gas key. Opening the gas port diameter will help but you get rapidly diminishing improvement once that diameter is equal to the inside diameter of the gas tube.

I don't buy the argument that the cartridges are too heavy in the magazine stack. That's just silly. I've shot 50 Bewoulf with 600 grain bullets with no problem in standard AR magazines. A test is to shoot just one cartridge. If the bolt doesn't lock open you don't have an adequate gas impulse. It could still be inadequate even if it passes that test.