Seems to me that if a gas check was put in with the open mouth facing the powder it would act like a lip seal and completely seal the bore and allow the use of dead-soft lead as is used for muzzle-loader balls. I've tried many variations of cast projectiles and always ended up with severe leading due to the fact that the only lead I have is pure (5 BHN) lead. My molds don't have grooves that can accommodate checks, and I haven't thus far found any molds available that do, any comments?