I have killed many deer with 12g slugs through a slug barrel. an ounce of lead through the boiler has always had a pretty significant terminal effect.
Some folks around here push slugs through thier regular shot barrels with good results, they've been doin it that way for years. Just realize your limitations and stay within them- ie range, accurracy, etc. If using a plain bead sight, you might be good out to as far as 75-80 yards but most will find 50 or less very reasonable. You need to do some experimenting with your SG and a couple different brands of slug. Don't waste money on sabot loads in a smooth bore.