Looking forward to seeing your results, 450.
: Since shooting the heavy recoiling bore rifles can be a challenging affair, I've come to the conclusion that sitting down and firing off 10, 20 or more rounds from the bench while testing loads, can be wearing on the nerves & give false results. The most-important 1st and 2nd shots led me to try a different approach.
: I've tried, with good success, in sitting down, and shooting a left and right, or couple from a kicking single, then changing targets and guns, shooting something easier and totally different, like a small centrefire with scope, concenrating on trigger squeeze and getting tiny groups until time to clean and or let it cool down. After that, I go back to the double (or single) and fire a couple more on top of the first two. I find more times than not, I don't get the flyers that make me think there's something wrong with the load & get a truer representation of what the big one is really doing. We are there to test and develope accurate loads, not to test endurance.
: This system works well(for me), even with a little .458.
: Another thing I found, is to grip the forewood in the left hand as if in a hunting position. The left had rests on the bag merely to steady the sights and get a good hold for load and sight testing. This changes the recoil impetus to the same as if in hunting situations. This goes for all kickers. My .458 needed re-sighting to have bullet impact actually be true. I had to raise bullet impact by 4" compared to the bullet impact if the gun was allowed to bounce off the bags. Some guns create even high impacts if not held, like a little .45 Colt M94 Trapper. It delivered excellent 1-1/2" groups at 100yards, whereas if allowed to bounch with traditional bench techniques, gave erronious grouping, flyers and extremely high impacts, 12" over what a held gun did. BTW - there's no flies on a 320gr. to 340gr. cast and properly sized rifle bullet doing 1,700fps from a 16" barrel. It took 2 elk for me in good fashion. Had I not re-tested with proper holoding techniques, I'd have missed.