The thicker 243 WSSM brass is more difficult to resize than most, perhaps more so because mine is fired in an AR and may expand more than it would in a bolt gun.
I've found that a good case lube is extremely important; Hornady Unique works much better than Imperial (cases lubed w/Imperial squall like a banshee).
I like mine, but what's not to like about a D Tech?
If you get one, be sure to get one of reb8600's brass catchers, 'caus you can't afford to lose your cases. Luckily I foresaw a looming brass shortage for the WSSM's and picked up an ample supply of brass. It's getting hard to find now.
I did the same, used 243 wssm brass for the 300 ossm. Still have a couple of new bags of winchester brass. Trying to see if it is a big difference from my 6.5 grendel.