I'd as I said give some serious thought to a single shot. Preferably one with a 26" barrel. This will give you a few more inches to build a littel more velocity. Even with the 26" barrel it will probably be shorter than a bolt with a 24". If you go with a higher quality/price action to start with it should be sized to the round and the gun will/should weigh less than a bolt as well. Though you sound tempted to go smaller than 25 cal I wouldn't do it. The heavier bullets of a slightly larger caliber will hold their velocity and energy better for those long shots.

Bill