Reloader 15 is a fine choice. I am switching to it after using IMR4064 for many years. Both powders work well with 250 grain bullets. I have not used the 225 partitions, but I can vouch for the effectiveness of the 250 grain Speer grand slam as a very god "big critter" bullet, and the Speer 250 hot cor and the Hornady 250 interlock have worked just as well for one animal each. A 250gr. at 2500fps has been my standard elk hunting combination for about a dozen years, I killed 10 elk with that combo, with no problems at all.
The two bullet failures I had with the Whelen were both 225 grains. In one case I shot a whitetail buck through the ribs with a 225 Sierra BT at a range of about 10 yards. That buck ran more than 100 yards. There was only a tiny bullet sized hole all the way through. No expansion at all. Others report these bullets occasionally blowing up. I will not use another Sierra 225 BT on game.
The other was a Nosler 225 gr Ballistic tip. This one was my fault, I shot a bull elk that was angling away from me, placing the bullet in the paunch expecting it to penetrate to the vitals. It did not, and I lost the badly wounded animal after tracking it for hours. Learned some hard lessons that day. I punched my tag with no elk meat to show for it. And caused a fine animal to suffer needlessly. I had expected a bullet designed to open easily at long range to penetrate like a tough bullet. My only excuse was that I had shot several elk and moose with the 250 grand slam bullets in the years before, and those bullets would penetrate a full body lengthwise. So I expected the same, and chose to take a bad shot.
I recovered one 250GS from a cow elk that was feeding towards me at about 150 yards. Shot her in the withers, top of the neck. I recovered the bullet under the skin of her ham. It had broke several neck vertebrae, went through lungs and paunch, missed the femur and stopped at the back of the ham. The only other 250 grain GS slug I've recovered was from a moose shot in the throat at very close range. That bullet was found about half way back after breaking about 10" of neck bones. A Barnes 225 X was found under the skin of the off shoulder of a bull elk after it broke both shoulders and ribs on both sides. Range was about 80 yards on that one. All the other bullets used to shoot about a dozen other animals exited and were lost. But the kills were decisive. I'm sure you will like your Whelen.
