That FN will be an interesting gun. If a normal lever-gun chamber is cut, I would be surprised to see 2,000fps with that bullet.

Standard heavy Marlin .45/70 and .450M ballistics are what Frank Barnes had in mind when designing the .458 2" bolt rifle ctg. -around 2,000fps with a 400gr. seemed to be his goal.

Wil Hafler has an excellent article on the .458 2" in Big Bore Rifles and Ctgs., but his loads are, I assume, for a shorter throated chamber than I had. Still very impressive @ 2,150fps with 400gr.

H335 is one of the best powders for this round, I found. I used 68.0gr. for 350, 400 and 500gr. bullets and all sub MOA to 200 yards. There was not the spread of velocities you'd expect. I also experimented with John Buhmiller's double primer loading for straight cases - with excellent and surprising results, but that's another topic.