Here we go with the how much can you over think this sport crowd. A grade five bolt of the proper thread count is many time stronger than the old wrought iron plugs used in every antique longrifle. Unless you are going into this build with the plan to grossly overload the piece, it seems you are worrying about nothing. I had a friend bring in a trade gun for repair that I helped him build.he had been hunting in Idaho in the winter, and let the ramrod slip up through his numb fingers while pushing the overshot card down on a load of shot while grouse hunting. the gun had all the barrel pins bent, both lock bolts bent, the upward tang screw bent, and a thumbnail shaped chip out of the stock at the tang. The breech plug was a grade 5 NF bolt with a tang welded on it. No threads were pulled, or showed any signs of damage. The pins, and bolts, were replaced, and the barrel was check for bulges, rebreeched with the original plug, proofed, and is shooting today.
Hungry Horse