I field trial dogs off horseback and have a need to carry a shotgun on occasion. I have a Winchester Model 50 12-gauge semi-auto with a 30-inch barrel that I was going to sell, but they are only bringing about $200 to $300. I am thinking about just cutting the barrel to about 20 inches and using it. I would carry it unloaded while in the scabbard. Thoughts?

Absolutely.

You might see if you can find an extra barrel to cut and keep the original for field use if you want to use it that way. Nothing wrong with a shotgun as a saddle gun.