I will be real interested to see how well that GMB Sharpshooter barrel works for you. They are supposed to be good conical shooters.

As for long range, I have no experience. Only what I read. For instance the Whitworth required a special hexagon shaped conical. And the barrel had to be basically cleaned between shots. They were very slow loading from what I read but also very accurate. As to whether one brand is better then the other... again, sorry no help here.

Other long range guns were the Gibbs rifle made in England. Queen Victoria I believe it was actually shot and hit a target at 400 yards with a Gibbs during a shooting match. Shooting matches used to be very popular. The Gibbs is a Pedersolli and they too are .451 or I think they come in a .40 caliber as well. I had someone asking me about loads for one once, and I told them if they owned the rifle and had a manual, they had a lot more knowledge then I had.

Another rifle to consider is a target model Sharps. Some of them were able to pull off some extreme distance shooting. In fact after the introduction of the Sharps, many shooting clubs (after the war)wanted them banned from their matches because they felt the Sharp had an unfair advantage.

Long range rifles are fascinating to say the least. That is why that Sharpshooter barrel has my interest. Be sure and post some results on that for us/me.