I have a Encore Bull barrel, 15" w/2" break. It is a rifle barrel cut down. You talk about a shooter. It likes 80 to 100 grn bullets. I have taken Prairie Dogs easily out to 300 yds with the Bushnell 2x6 scope and 100 grn Sierra Pro Hunters.
I have taken deer and I loaned it to a buddy and he took a antelope with it.
If you want a great 6mm round that is easy to load for and a good all around caliber the .243 is hard to beat. Here is mine cooling down after some hectic Prairie Dog shooting.