41 gas checks

[Motor]

I don't see why the inside diameter of the check is that important as long as it's within reason and will fit over the base of the bullet.

What's more important is the material thickness which will determine whether or not the check is going to be crimped on to the base. The material thickness x2 subtracted from the diameter of the sizing die being used should be at least one to two thousands of an inch smaller than the base of the bullet.

Motor

[Minerat]

Motor,
I don't know why, I just know that if you try to seat a 416 on a 41lt based boolit it will not seat properly. I think what happens is that the crimping process causes the GC to stretch so it hits the bottom of the first drive band and does not crimp properly leaving it loose. If you use a nose first push thru sizer then the check deformes at the base so you end up with a bulged base not flat like is ideal and in some cases is loose too.

[Motor]

Motor,
I don't know why, I just know that if you try to seat a 416 on a 41lt based boolit it will not seat properly. I think what happens is that the crimping process causes the GC to stretch so it hits the bottom of the first drive band and does not crimp properly leaving it loose. If you use a nose first push thru sizer then the check deformes at the base so you end up with a bulged base not flat like is ideal and in some cases is loose too.

I've experienced this bulging at the base you describe crimping aluminum checks on the Lee 55gr .225 going base up. The bottom of the checks come out with a shallow dome shape.
I personally don't use gas checks for any pistol boolits. I bought a box of Penn hard cast bullets many years ago that are 18BHN and actually have to shoot them with magnum loads to get them to obsturate enough to seal.

I recently bought a Lee 210gr mold so I could shoot lighter loads. About 3 years ago I started using powder coating. With powder coating I absolutely see no need for gas checks on pistol boolits. I can't make the same statement regarding rifle boolits, yet, and may not ever but when drivin at "normal" cast boolit velocity I've not seen any issues.

Motor

[TomAM]

Motor,
I don't know why, I just know that if you try to seat a 416 on a 41lt based boolit it will not seat properly. I think what happens is that the crimping process causes the GC to stretch so it hits the bottom of the first drive band and does not crimp properly leaving it loose. If you use a nose first push thru sizer then the check deformes at the base so you end up with a bulged base not flat like is ideal and in some cases is loose too.

That could certainly happen with a GC shank which is the wrong length.