Standard answer, read the FAQs, it's all been said before.
Instead of the O-ring, try a piece of refrigerator magnet about 1" long and the width of the barrel channel, placed 1" from the tip of the forend. I've used this method on several rifles that vertical string, Fred also mentions uplift on the forend tip in his accurizing tips. I used this trick on my new .444 before I even shot it, you can see the results on the target below.
H&R will do a free trigger job when you send it in for accessory barrels or repair, just ask for it on the order form. Any gunsmith can do a trigger job, they aren't hard at all, many, many first timers have done them following the instructions posted in the FAQs.
Tim
