A year ago, I tried loading some 243 Win for a Mossberg Patriot youth gun. Goal was 1 MOA with bullets for deer hunting. Never got close to that....not sure if it was me or the gun. But my loads were at least as good as factory ammo in it, so left it at that.
Anyway, as I was looking for powders then, what became apparent is 243 is an enigma. Manuals all suggest faster powders in range of 4064, 3031, Varget, etc. Same group you might expect to find with 308. Yet a lot of guys seem to have good success with slower powders in 4350 and 4831 range. What it came down to for me was there was a cut line for bullet weight. 85 grain and less bullets......faster powders. Heavy bullets.....slower powders.
If I had a 243 with 9 1/2 twist......and wanted to pop targets, would be looking at some Match Kings in range of 100 grains, either one of the 4350's, and work it till it worked.
But there is a 2nd part, Since OP is popping targets, if this is to be a fun experiment, then let it be so. Find a baseline that you know works, then branch out from there. Try to duplicate or better your best success with something else.