With the introduction of rifled barrels for shotguns, it has been only a matter of time that the cast bullet fellows picked up on it....and that's great!
May shooters soon realized that a rifled barrel on a shotgun was now a ultra bore big game gun!
Problems arise in thinking due to them still thinking in terma of the old Foster designs.....it's an entire different game when going the full bore.
But....all youhave learned about cast bullets in handguns and rifles still apply to there big full bore bullets.....including, and most important, heat treating!
The following are some thoughts:
(1) Unlike shot loads, in a shotgun, that like a soft cushsion to reduce shot deformation......full bore laods like< and must have for accuracy, a firm platform. The best 12 ga. wads we have found are from Circle Fly. They are the .250"-1/4" hard nitro type wad....and the 3/8" hard filler wad. The best overpowder wad for plastic hulls is the X12X sold by Ballistic Products Inc. These wads, in combo, with you powder to give a wad column and a firm rolled crimp...will amke a good load.
(2) Time and time again, when testing factory Foster slugs....when accuracy went out the window, it was due to wads blowing into the hollow base. If you are loading this design, it is most important that a Circle Fly .250" hard card wad be under the slug.
(3) One of the problems in rifled shotgun barrels is the old type forcing cone. Custom barrels have leades like in handgun, or rifle chambers. in order to get accuracy in rifled shotgun barrels, the slug bullet must be hard and aligned as it leaves the hull. This is where heat treating and hard wads come to play. The best way to heat treat is to cook the slug/bullets for a hour at 400/450 degrees and water quench. This will run the bhn up to around 30 bhn and the slug/bullets will stabilize at around 28 bhn. Wheelweights, and a liittle tin, heat treated this way will not be brittle.
(4) On the question of lubes. The slug load does not need to be lubed as well as ceterfires since the velocity and pressure is lower. Lee Alox, or #350 Alox, cut back with paint thinner, makes an excellent Alox wash.
(5) Slug size is important. Modern rifled barrrels, like the Hastings, runs .727" -n the grooves and .717" on the lands. In slug/bullets as large as 12 gauge, .003" over size of groove is best. Bigger and you will get some mis-alignmenet. Dixie has settled on .730" as a standard.
(5) The cast bullet shooters will have to find a mold maker to cut your mold so that it throws the slug/bullet, with your alloy, at 730". We prefer a lathe cut iron mold for our production molds. Some, but not all, cherry cut molds are not true around. This may be OK for soft slug/bullets, but is not best for hard cast heat treated ones.
(6) No diiscussion would be complete without touching on powders. Powders in slug loads do not react like the same powders in shot loads. There is a small peak in oressure as the hard slug/bulle enters the rifling and with slug/bullet weights over one ounce (437.5 grs)....a owder with the burn rate of Blue Dot or Steel is best. One ounce and less, a burn rate about Herco works. Stay away from the faster powders with hard cast heat treated slug/bullets.
(7) Pressure testing ypur loads is smart. Ballistic Research in McHenry, Illinois, is a very good place.
Just some rendon thoughts, James