With the nose piece inlet tightly, you have two choices...drill down through the barrel channel's bottom flat right out through the nose piece. Depending on the cap's length, one or two copper rivets is what I'd use. Or, drill through the 45 deg. flat of the channel - one each side, out through the cap, and again, copper rivets in brass look fine to my eye. I've also made rivets out of brass cutler's rivets or brake shoe rivets.