The Wingmaster is a great pump action design. Been around for decades. If it is an older design, the barrel may not be safe for modern steel shot. I'd check.

The design of the Foster type slug is that the rear end, concave in shape, creates a weight forward projectile with a rather thin lead walled "cup" at the rear. The projectile is well "under" gauge and absolutely safe for use in a Full choke barrel.

The Foster idea is to use the pressure to expand the walls of the rear cup and seal the bullet against the smooth bore so that the bullet gets the optimum muzzle velocity. The "angled" grooves on the slug bite into the air and that is what spins the bullet along its horizontal axis. As is well known, this spin is what stabilizes the bullet. Unfortunately, the Foster type slugs are not stabilized well until some distance from the muzzle. They are definitely not as accurate as a rifled barrel/sabot set-up.

I have shot Foster type slugs in a smooth bore 12 ga. pump. About 60-70 yards of good grouping is all I could expect. In addition this "biting" into the air eats up a lot of energy that would otherwise be conserved in the bullet's velocity. The slug looses speed rather abruptly and drop is usually very dramatic after about 75 yards. As already mentioned, a great way to go for deer hunting is to buy a rifled barrel. Using a well made sabot, you can expect very good groups and enough down range ummph to kill cleanly to 125 yards. If your Wingmaster's receiver will handle 3" shells (see information stamped on the barrel), I would suggest them for deer hunting.