I had a similar problem with my slug barrel. I also have the hammer extension on my Encore and when I called T/C, they said that the hammer extension will void your warranty. This is something to think about. If they see the screw marks, they could cancel your warranty. I still have mine on because I use so many different barrels and some make it hard to reach the hammer.

Now about the misfires. I installed a Bellm oversize hinge pin and heavier locking springs. These solved my problem. I am going to look into the heavier hammer spring also. Keep us posted on your results.