I make wads for any caliber straight-walled pistol using milk jug plastic.
Some years back when ALCAN used to make over-powder Nitro wads from card board and then along came the plastic revolution and ALCAN started marketing a wad to hold the shot in shotshells called a QUICKSERT.
It started out flat with a circular bottom cut to fit the inner diameter of the shotshell. Attached to the circle were a set of flat wings , one each side that folded at the attachment and each formed a semi circle that met inside the case to form a tube when the circular bottom was pushed inside the case and bottomed out atop the overpowder wads. The shot went inside this QUICKSERT and then the crimp on the shell was last.
With some careful measuring , a plastic or even thin paper model made, and a tin template can be made to size these to fit any case, including .444 Marlin and . 45/70 down to .32 and .25 pistol.
These QUICKSERTS will ride out encapsulating the shot with no leading and a better pattern further out.
Sure, it takes a little extra work to use a shot sleeve, but it keeps the lead from contacting the rifling which swirls the lead and blows holes in the pattern till it's just too skimpy.
The shot sleeve slides past the rifling unless you load it too hot or try to pack in the shot.
Shot doesn't compress too well.
Loosely packed and only a couple grains of powder and you get killing patterns.
Try it before you load those screaming shot blasters.
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