I put off bending he barrel on my first trade gun, until I just got sick, and tired, of getting my butt whipped a every smoothbore shoot. In the end, I did it myself, with a homegrown contraption made from a conduit bender head, a small hydraulic jack, and a couple of modified "C" clamps. You only really have to bend the barrel enough to overcome the taper in the barrel. However, you do have to over bend it quite a bit, because there is quite a bit of spring back in most barrels. I say "most" because the barrel I used was an old shotgun barrel from the eighteen eighties that had very little sling back to it. But, I have since bent modern barrels that are very springy. These springy barrels also have a habit of straightening out over time as well, so you may find your trade gun losing accuracy after a lot of shooting, and have to rebind the barrel.
Hungry Horse