Leading in the Trapdoor occurs with using too small diameter bullet that does not fit the barrel and/or too hard an alloy that won't allow the bullet to "bump up" or conform to the barrel. If the bullet doesn't fit then gas blow by will cause cutting of the base of the bullet and deposit lead in the bore. If the bullet fits and has a decent lube you will not get leading to any significant degree at 1200fps or even more. This generally means in these rifles a soft alloy (typically 30:1 to 16:1 lead to tin) cast at 0.460 or more diameter with enough powder charge to cause the bullet to "bump up" and fill the bore.

Jerry Liles