R@W,
Just curious what type of sighting system you are using. Did you get it drilled and tapped and add a scope or are you using the bead sight? Other than that, I would suspect at the very least a larger dia. bullet. Mine slugged at I think .452, and when I used lead I was sizing mine to .454 and having better results. I have also found a very high loss in velocity with the short 45lc in this barrel. My solution was going to a longer type of brass. I started with a 444marlin case fireformed and started have decent results, but really made it shine with 9.3-74r cases trimmed to fit my chamber. There is good info in the FAQS on 45/410 ...read the thread and you'll also find a post to my thread on the project. I put alot of time into accurizing mine, and others have also. I had alot of unburnt powder at first and then started using a very firm crimp with the Lee factory crimp die, with improved results. Another thing I would recommend if you go the longer brass is to get the chambers cast and go over the dimensions of each chamber,...they may be different for each. Billy (above) went a different route and used brass shotgun shells to load his with some good results.
Hope it works out for you,...I remember thinking the same for my barrel, as a good youth starter, but I don't think this barrel shines on either chambering unless you go to some effort on your part.
Jerry