My throat on mine is still std dimension.... but I have a stock of the old 2 diameter 150 & 175 gr Corelokts that I will load with an old batch of 7828 and H570 & H870 to see if one can actually hit those 1962 velocity figures. Also have a 26" ss take off barrel to replace my current one when it goes. MB
The 7828 would be the best of those you mention, but 4831 would be a better choice imop.
The H870 would be a poor choice due to the slow burn rate. You couldn't get enough in the case for best results.
As an example, for many years lots of us used H870 in our 7x300 wbys with 162 gr Hornadys. My load was 90 gr in a 700 action with a 30" barrel and it ran around 3200 fps. 79 gr of 7828 in the same gun with same bullet gives over 200 fps more
and its not nearly as temp sensitive in cold weather as the H870.
Mind you now thats not a 7 Rem, our load for that is 65 gr 4831 with a 162 gr and it runs right around 3000 with a 24" barrel.
As for the H570, id be very carefull with how you use it due to the value of it. It is as you might know WW2 surplus powder, and there is nothing today that im aware of at least quite like it. For decades it was the go to powder for those of us using then wildcat 30x378s with 36" barrels for long range hunting. 112 gr in my gun would drive a 200 gr SMK to 3500 fps with no problem. Howard Wolfe wouldn't build you a gun if you didn't have that powder. Even today, we still use it in our large 338s, like the 338x378 and the Chey Tac type case.
My sons best load is 110 gr H570 with a 300 gr Berger in his 338x378.
