My .357 mag. was shooting all over the place at first, too. It came with scope base and that base was not only loose, but mounted crooked, too. Scrapped it for a picatinny rail and scout scope. Made all the difference.
Another thing to think about....as said above, is you don't need a crimp in a rifle. That means you can seat the bullet much further out, leaving much more room for powder. I've worked up a load with the 140 gr. FTX over 20 gr. of IMR4227. I don't have a chronograph, but it should be ~2050 fps MV. The FTX bullet is seated about 1/4" deep and the powder is slightly compressed. Absolutely no signs of excess pressure. By the way. the 140 gr. FTX has a lousy ballistic coefficient. The 200 gr. FTX is far, far better, ballistically. A true spitzer.
Next, I ordered a box of 200 gr. FTX and expect to get ~ 1600-1800 fps out of my 16.5" barrel. This is a WAG. I haven't worked up that load yet, but I am fairly sure I can get there. Maybe even surpass that MV with H110. This puts the 200 gr. FTX in a magnum case at a similar MV of the max. load in the Maxi. Hodgdon says 18 gr. IMR4227, 200 gr. bullet at 1440 fps in a 10" barrel.
I'm assuming you have the SAAMI chamber with the long forcing cone/throat that allows seating the bullet way out. Ideally suited for spitzers. If you do and can load your own, experiment. Tailoring your ammo to get the most out of your rifle is what handloading is about.