gunboat57 wrote on Jun 11^th, 2013 at 2:04am:

Parashooter, not to derail the flow of this thread, but did that bullet in your picture sized to .312 and fired in a .303/.313 barrel show symptoms of leading when fired for real, not a squib load?  Will the gas check keep it from leading even if the bullet is not .001" over groove diameter?

I suspect you may have fallen prey to the popular myth that undersize cast bullets cause leading via some "hot jet of flame" squirting past the naked alloy in the grooves. I'm afraid that one's as thermodynamically bogus as the idea that undersize jacketed bullets cause erosion in the grooves by "gas cutting effect." (Essentially, the amount of heat in any escaping gas isn't great enough to melt bullet alloy during a very brief trip down the barrel - much less barrel steel. The vast majority of hot gas remains behind the bullet.)

The true causes of lead fouling are complex and poorly understood, as are the demonstrable benefits of the gas check at higher velocities. I haven't had any leading problems with cast bullets in medium military rifle cartridges when loading them to appropriate velocity for the bullet's configuration. Short, light bullets with a high ratio of lube to bearing surface can be driven faster without leading than long, heavy bullets. Hard alloys help avoid leading at higher velocity, but sometimes produce less accuracy than softer alloy at less speed.