Dale Atkinson built a .40 cal. flinter for me back in the fall. I take it to shoots and have done very well with it, bringing home a lot of meat prizes. He built it as a target rifle, double-set triggers and a crescent buttplate. I shoot a .400 PRB in front of 50gr. GOEX 3F. It shoots tight groups. I probably won't hunt with it as I have two squirrel rifles (a .32 and .36) and several deer rifles (.45, 50, .54, .62 smooth rifle)and several smooth bores (.62 and .73), all capable of one-shot kills.
I do find the .40 to be an "interesting" gun, in that I am constantly amazd at what it will do. First Frontier Militia of Bowmanstwon, PA has 75 and 100 animal silhouette targets as part of its aggregate match and the .40 is good-to-go on these as well as the closer targets.
I have shot balls as small as .389" and everything I have shot through it shoots well.
James