23 February 2011
I think Keith mentions the primer tube/duplex/forward ignition stuff in his autobiography, and a few times in his other articles. If you have access to those you could get the definitive answers.
My own summary from memory is that the tests with .50 BMG were done for the government, but ended with the war. There was a measurable gain in accuracy using the system, but, apparently, not enough to justify switching to that system. Especially with the war ending.
There was also some gain in accuracy with smaller, civilian calibers, but, again, the novelty and complexity militated against wide acceptance. Some folks testing the system published articles that claimed pressure increases. I would guess that is a possibility since some of the powder space was taken up by the tube. So, just reduce the powder charge a wee bit!
My own opinion, for what it is worth is that the system makes some sense for single use cartridge cases because of the complications involved in trying to easily decap thru the flash tube for reloading. Also, it does make theoretical sense that igniting the powder charge from the front would reduce erosion from unignited granules scuffing against the leade, etc.,as they are shoved forward by the gas building behind them. I would think the use of powder whose grains were too large to fit down into the tube would be required for consistency of ignition.
Seems like at some point during the late '50s or early '60s you could buy those tubes. Instead of being threaded, they fit thru the flash hole and were flared on the butt end so they could be held in place by the primer itself. I believe I saw them advertised in Guns and Ammo and Shooting Times.