Unless these steel BBs are the softer variety used in modern suppository guns for shooting Migratory Waterfowl, AND the barrel of your shotgun is made of steels that are rated safe to use with these "non-toxic " steel shot loads, I would not use such a bag of shot for anything OTHER THAN a rest for my rifle at the bench.
You might be able to use these If you make a Shot cup using 2 strips of Mattress ticking, oiled, and laid cross-wise on the muzzle, to give you a double layer of protection, keeping those pellets from rubbing against the bore. Each strip should be wide enough to cover half the circumference of the bore with a bit of overlap, so that NO pellet can rub against the bore. Use a small Gauge wad inside the cup to maintain the shape, and help "release" the column of shot at the same time, after the "leaves" open up on the fabric cup. Tighter patterns Might also be obtain by inserting a Card Stock collar inside the fabric cup, before the shot is loaded, with the length of the collar being enough to encircle the shot column complete with some overlap, and the width of the collar being "tall " enough to provide a protecting barrier between the entire height of the shot column and the fabric cup. The Collar will separate from the pellets After the leaves of the fabric open, delaying the separation of the load of shot for a few milliseconds, and allowing the column of shot to travel a bit further down range before the shot begins to open up into a pattern.
Shot collars made of early plastics were used before we had One-piece, molded Shot cups for suppository shotguns. Since Plastic is Not traditional, and really has no place in shooting a MLer shotgun(IMHO), tough fabrics, and paper collars can be substituted for the plastic.
The nice thing about fabric cups is that they can be made to fit barrels with muzzle chokes, either fixed, or screw-in types. Given choked barrels, these cups can produce even tighter patterns at ranges out to 35 yds, and possibly beyond.
Most of the .177 BBs are and Were designed to be used in spring loaded, and Air "BB" guns, Not in Shotguns. :hmm: :surrender:
The BBs Steel "shot" made for shotguns are a true .18" in diameter, and cannot be used in the BB guns without damaging and ruining those brass tubed barrels. ( They don't do a lot of nice things to the few steel barrels found on high-end BB guns, either! :shocked2: ) IN both cases, if you can even get a .18" diameter steel BB into that air gun, it will most likely be stuck in the barrel, and the barrel will be ruined trying to remove it. This comes from two different dealers in air guns who have had dozens of such guns brought back in for repairs, and had to order new barrels for the guns.
:surrender: