Just using gas checks alone will NOT prevent leading!! Your bullet alloy must be hard enough to withstand the pressure levels to which you are loading, your bullet must fit the bore correctly, and your bullet lubricant must be adequate also. If ANY of these factors are not up to snuff, you' ll get leading.

As a matter of fact, a correctly-fitting gas-check cast bullet made of the correct alloy, heat-treated to adequate hardness and using the right lube (LBT Blue lube)can be driven at velocities up to, and sometimes exceeding, 2700 FPS!

To make bullets hard enough, make them from an alloy containing lead, tin, antimony, and a little arsenic. Then heat-treat them. Wheelweights are usually of a good alloy that can be heat-treated.

I recommend that you obtain the handbook called something like JACKETED VELOCITIES FROM CAST BULLETS from the Lead Bullet Technologies (LBT) company. Some other handbooks, like Lyman' s Cast Bullet Handbook, also contain info on bullet hardness vs pressures, how to heat-treat bullets, etc.