I have a few MGM barrels and a couple Preferred Barrel Blanks (their bolt gun barrels). I have only had a problem with one of them. I have a couple of Bullberry, a Bellm barrel, and a couple of EABCO barrels as well. All shoot well.
I like the 6.5X47 round. It is very efficient. It should work very well in that Encore. 6.5 BR is another fun one. Just get 6 BR brass and neck it up. The 6.5 BRM from E. Arthur Brown is also a pretty good choice. It uses rimmed brass so insertion and extraction in the break-open guns is a bit easier.