The wssm's are a bit different to load for. I think their biggest problem, and really the only "flaw" in the design is that when Winchester/Olin designed the brass, they did so by just sizing down WSM brass to wssm size. That was their plan for making the production brass. I can understand from the manufacturing standpoint why they did it, to save money.
The downfall to that is it made the brass thick. Really thick. Both the case body and the case neck are ridiculously thick. You'll be looking at neck thicknesses in the 20 to 22 thousandths. If you measure the case necks of just about any other "common" bottle neck rifle brass, it's typically in the 12 to 16 thousandths range.
This has a couple of negative effects. First the brass is "hard", really hard, and you will have to load at the upper end of the load charts to get the brass to seal in the chamber of your rifle. Sooty necks is a common symptom with handloads. More importantly is neck tension. The wssm brass has loads of neck tension. With the thick necks, you get more springback of the neck during resizing, and you'll typically see neck tensions in the .003 to .005 range. That's a bit high with regular neck thickness, but it equates to much higher neck tension in the thick necks of the wssm.
This means your pressures will come on quick, and early during load development.
One of the more common "fixes" is to anneal your brass often, usually every 3 or 4 loadings. Also annealing will make it easier to bump the shoulders back during resizing. You will likely need to "cam over" your press during the resizing operation to insure you're getting the shoulders set back. Try test chambering a resized piece of brass in your rifle while you're setting up your resizing die to make sure it will chamber. Hard chambering reloads can be common if you don't do that step.
If you can get your hands on some Federal 243 wssm brass, it is of better quality and thinner body and neck than the Winchester brass. It will help with the problems.
I still remember my first batch of handloads fired in 25 wssm. When I set up a new rifle, I usually start my test loads half way between the "start" and "max" loads listed in the load tables, and work up from there. It's never really been a problem before. The very first handload I fired locked the bolt up, and I had to use quite a bit of force to open the bolt handle. I had a good friend and long time shooter/reloader with me at the range. I remember firing the round, reaching up to open the bolt, and looking at "Red" and saying "Uh-oh. We have a problem." I tried 1 each of each of 3 different "start" loads I brought with me to the range, and each one was way too hot, requiring the bolt to be forced open.
Start with the starting loads, work your way up carefully, and watch for neck tension and pressure. If you go over to wssmzone, there's a bunch of topics on over there that go into great detail on the whole wssm issue. If you search under my user name and "neck tension", you'll find a bunch to read there. I used to post over there a few years ago when I had my 25 wssm.
Good luck.
