Not always for the gas check from what I understand. I have pushed harder than 1300 FPS with some, and did not have any problems. In fact I pused some .41 Mag past 1400 FPS (24 rounds to be exact) My gun cleaned up with a few wet patches, and bore brush. I use M-Pro7 I clean at the range while the gun is still warm it is much easier that way.
I did not stick with that load due to the fact that my loads that clocked at about 1280 FPS shot the most accurately. The veloctiy did not give me any increase in accuracy so I stuck with the lower velocity load. 210 grains at 1280 will still put a world of hurt on what is hit by it.
I do not use gas checkable molds. All of my molds are Lee 2 holers, with the exception of my .45-70 that is single cavity, hollow base mold.
From what I hear you should be able to shoot without gas checks. Though with every hand gun load I have worked up the top end of velocity did not get me the best accuracy. For the most part middle of the road netted the best accuracy.
This was a 12 shot group at 15 yards standing isocolese stance shot about 2 to 3 seconds apart. Note theese were .38 Special. My phone died before I could take a pic of the .357 Mag loads. Groups were similar to the ones pictured.
If you want magnum loads I suggest AA#9 over Alliant 2400. It is cleaner at lower pressures, and from what the chrono said more consitant from shot to shot at lower velocities.
