It’s good you understand the terminal ballistics between bullet types, especially in this High Performance Cartridge. You are miles ahead of some so called experts. There was a highly regarded genius on another board who used a 50b, which primarily uses bullets designed for the 50AE, on a deer this year and posted his shocking pictures, with a pathetic story, that was picked up by PETA, who for a time used him as their Poster-Boy. Needless to say he horribly blew up (nearly off) the shoulder. The deer got away and was later dispatched by another with a 7mm Mag. Our hero thought the bullet just fell out, he had no understanding of what actually happened. A pistol bullet designed to expand on soft targets at range and say maybe 300fps, will blow up into thousands of little specks on big game at 1800fps+, with no penetration into the boiler room. To be sure the same thing can happen with the 450b, so choose bullets that will accomplish your mission properly. The opposite can also happen, bullets that are designed for thick skinned big heavy game and rifle velocities, will not expand at all on thin skinned deer, and are inappropriate for home defense, it is not wise to use some types .458 bullets that will take out elephants or Planes Buffalo on deer or other targets that may need an expanded bullet or no penetration at all. Which is why I say the 450 Bushmaster is the most versatile, AR-Big Bore on the market. Use pistol bullets when zero penetration is needed, like 180gr-230gr hollow points, which will not penetrate a common house wall reliably, sure don’t want to kill the neighbor’s dog now. Choose fmj’s when penetration is needed and Flat Point FMJ’s when penetration and tissue disruption is most desirable. As a note here, the FP’s disrupts more tissue than an expanded bullet does after it expands and the FMJ-FP penetrates any animal on this planet, killing elephants, Cape Buffalo or deer with equal ease. Keep in mind that 230gr fmj round ball bullets work well in big game too. Think of it this way, though that bullet won’t really expand, 45 cal is already bigger than a 30 cal gets after it expands, so shoot’em if ya got’em! If bigger heavier bullets are desirable, then buy them, they are available or get a Lee lube-sizer die set-up (about $30) and shrink down .458 bullets, we’re only taking them down .003” per side, two and a half times less than a standard human hair. I’ll take a soft lead lubed .458 bullet and use it to lube the die for every 5-10 jacketed bullets or use some Cast Performance .458/500gr bullets to lube that die and then you’ll have some really heavy bullets for plinking in your 450b, not necessary but fun and maybe quite useful. I often use 350gr .458 Hornady bullets, for fun, and do not experience any jacket separation at all in our hydro test or on the reported Buffalo that have been killed with this set up. In other words, it is possible to use .458 bullets in a .451 barrel, but 451-452 bullets in a .458 just does not work well, if hitting the target is the goal.
I can fill volumes with things I’ve been told and I do not know about the 454C problems you discuss (a call Causal might be helpful), but with no forcing cone on an AR and now millions of rounds of fmj’s through the 450b, I’d have less the zero worries about using the fmj’s in the 450b, in fact I recommend them for many applications. However, as stated above, using them in a 458 SOCOM will not work so well, bullet wobble down the barrel is the problem here.
Trim length is 1.700” plus .000”, minus .003”
Concerning your proposed 240gr/1680 starting load, Slash’s last load was 45gr of 296/H110- (their data is interchangeable) with a 240gr bullet, as I remember, as 1680 is going to lower the pressures for the same charge and extending the OAL to 2.250” will also drop the pressures and as 296 and 1680 have the same specific gravity, I’d start at 45gr of 1680 and work up, looking for pressure signs all along and stopping when necessary. But here’s a novel idea. I always like to know the max amount of powder the case is going to take when a compressed load is used, when developing a new load. I sacrifice a single case by drilling a 3/16 hole through the primer pocket. Then seat the desired bullet to the OAL of your dreams. Now, fill the cartridge through the new flash hole, make the powder flush with the base. Plugging the flash hole with your thumb and holding the bullet with your fore finger and pointing the case down, tap the cartridge with a kitchen spoon, many times. When you remove your thumb you’ll see the powder level has gone down. Refill again and repeat the process many times. The last time make sure the powder is again level with the base, now weigh this charge, this represents a slightly compressed load and should be the max the case can hold, with your chosen bullet. With some powders this will be of course way to much powder, but with the slower powders you may well get to this number in your developmental process. I hope I painted the correct picture here. I do this all the time, and as I’m not standing next to you, all bets are off, be careful. But here’s the goal, I wouldn’t by a Corvette to drive 25MPH, if there is performance to get I want it, but of course driving 200MPH has it’s dangers and so does handloading, be careful. One other warning, all powders, but most assuredly ball powders do have high pressure problems if undercharged…t