Don't get hung up on numbers. Especially when the difference is 50 ft/sec or less. I get 3100 out of my 300 Dakota with 210gr Berger hunting bullets with no pressure. Could push it harder if I wanted to. The 300 PRC is equal to or slightly superior to the Dakota. The 300 PRC has been developed and tweaked over 10 years of being around. We (DoD) have been killing people with it in places most Americans can't point to on a map, pronounce, or spell for 6 or 7 years. Just because Hornady introduced it to you and me a year or so ago doesn't mean they did quick and uncanny negotiation with the Marine Corps for the contract overnight. The Marines new well what they were getting well in advance. Qualified snipers regularly score perfect, or nearly so, at ranges WELL beyond a mile with the PRC. The reason it works so well is the case geometry has been optimized for 100% load density with optimal powders for this round. That can't be said for the 300 Norma, which is similar to what your Sherman Improved would be. When you load up a cartridge like that, the slightest tilt upward or downward in angle can cause a miss at those ranges if the load density isn't 100%. You have a sharper shoulder vs the Norma, but the issue is the width of the case up around the neck. Ultra Mags run into trouble with adequate magazine length with those projectiles optimally loaded because they're too long. Maybe ok if you intend to make it a single shot or spend a butt load of money with specially made magazine wells. Forget about the 30 Nosler, it doesn't belong in the conversation. Besides brass is RARELY available and when it is, it's twice the price of Ultra Mag brass and 3 times what PRC brass is. The only other option I'd seriously recommend is the 338 Norma, but you're going to have to have an action with a .750" diameter bolt because of the thrust. It's geometry is well designed, too.
If you "improve" the PRC, you've messed with the proven geometry. If 50 fps is that important to you, add 1 extra inch of barrel to your standard 300 PRC. You're going to spend twice the time and money and half your barrel life fire forming, and that's an art all to its own. Just the right fire forming load has to be used to get the cases consistently the same length and anywhere near the parent case length. That will get old FAST, not to mention expensive. The 300 PRC is the only great option here. You can get 3150 fps with a 212 grain ELD if you put at least 28" of barrel on it. That's an inch more than what's on my Dakota. I just built a rifle to do what you are doing and mine is a 338 Edge, and it's a single shot. I wanted to try a 338 caliber with over .800 BC available and the Ultra Mag brass was the cheapest among the available options. I had rather have had a 338 Norma, but would have had to have Defiance customize me an action the correct length with appropriate bolt face to make it just right. Too much money and time! I can do ALMOST anything with my Dakota that I could do with a PRC. No need to split hairs there. Good luck and let us know what you decide and how it shoots!
