Although I haven't used them in earnest for Smallies in a couple years, I had an instance of a 4 lb. 1 oz. Smallie taking one on Conesus Lake (Finger Lakes) in December 16, 2001.
Bait was a 3/16 oz. bucktail jig. Brown head with a perch pattern on the hair. No trailer.
I recall the moment well. I was over a shoreline point and cast it ahead of me into about 12 feet of water while drifting. I "popped" it back to me with gentle twiches of the rod tip. I felt that old, familiar thump and the rest was history.
That fish sticks out in my mind because I threw that hair jig out and got him right away. I couldn't get bit on it after that. Dragging tubes was really the way to go.
Hair jigs do seem to incite stronger productivity in the cold water months, no doubt due to the subtle presentations and lifelike motion of the hair (especailly with the "soft" hair types, such as rabbit hair) when the jig is still on the bottom. They are difficult to fish in windy conditions.
I'm no hair jig expert, but it would make sense to me that the ideal Smallmouth hair jig would have a lighter head - say 1/8 oz. (perhaps ¼ oz. tops with an appropriate trailer), but with a larger, light wire hook (1/0 or 2/0). So many times, we see small jigs with teeny hooks. That's great if they are used for fish like perch and small trout, but the larger hook will serve much better for the likes of bass fishing with them.
Good luck with your homemade jigs. Please keep us informed on the board as to your success with them, will ya?