Abner, and others who have asked about finding the kifaruforums discussion on allowable pressures of the Baikal/Remington SPR22/MP221 double rifle, here is the link, hopefully, to this most interesting forum.www.kifaruforums.net/showthread.php?t=6591&highlight=spr22&page=3
In the event this does not take you there, to page 3, search "Allowable pressure Sparton double rifle" Note that Spartan is misspelled, but do not correct. Get ready for a great ride if you want to know more on the subject and all the blather on 45-70 SAAMI pressures seems inadequate, the type often seen on this subject.
BTW, Tim Sundles of Buffalo Bore ammo, and a stand-up guy, confirmed for me recently the comments he made on this thread at kifaru 5 years ago. And I think Buffalo Bore knows a little something about potent 45-70 ammo.
I'm not really a big 45-70 fan and would have desired a British cartridge in my SPR 22, but I understand the need to sell guns and the 45-70 will do that. I've had a Ruger #1 Tropical in 45-70 for 25 years and a Remington Rolling Block with a Numrich barrel and custom fittings even longer. I have not shot them much, though I did make up a 350 grain load for the #1 with 3031 which was a real rocker.
One of the amusing topics on forums concerns whether a 45-70 can be a .458 Win Mag. Now, that is amusing, as it is not possible. But I think it begs the real question. The real question is to what extent a 45-70 can and is properly used for dangerous game, especially in Africa. That,...is a subject of ferocious controversy. You know the beat, the lever action/Ruger #1 guys want to blast dinosuars with it and the British rifle snobs with little practical 45-70 experience claim the round is a 'damned good woodchuck" cartridge out to 50 yards. All delicious stuff of course, but lacking in detail. I do note that in the last few years the boys at Rifle magazine have shot dangerous beasts in Africa with their 45-70 and they are still alive.
But I prefer far better authority than most. I direct you to John Pondoro Taylor's African Rifles and Cartridges. With all due respect to Craig Boddington, his African experience, his two Safari Rifles books, which are terrific, and a man who always is a gentleman and makes time for us little guys, I still think the 25 years Taylor spent hunting Africa makes him my expert.
The book has a page on the .450 Black Powder Express, the round popular at the turn of the last century and shooting light-for-caliber bullets of 270-365 grains. The 365 gr load was at 1700 fps and produces 2,340 pounds of ME. Taylor says the following on this round:
"I have used all four loads on different game and found them most satisfactory."
"I killed elephant, rhino, and buffalo with the 365-gr. hardened lead bullet, and lion with the soft solid lead bullet of the same weight..."
Interesting. Tim Sundles of Buffalo Bore loads a 430 grain LBT hardened bullet at 1900fps, with 3,500 ME, which he says can be used safely in the SPR22. Now, this is a much more potent load than Taylor's .450 BPE, which he found "most satisfactory" and we are to believe the modern 45-70 can't be used on big game? Doesn't sound logical. At the same time I recognize a "margin for error" inherent in more powerful loads, as did Taylor, as he later used more powerful rounds. Still, the modern 45-70 in the SPR22 gives comfort as a powerful round, while assuring a full recoil response in a 7.5 lb SPR22 rifle. It sure feels powerful!