100gr is the heaviest I've tried, the Speer in handloads and whatever Federal uses in their Power-Shok ammo, both shoot good in a couple of my 243s, one of em won't tho, it got rechambered to 6mm Improved and I'm gonna be working with the 87gr Vmax too, but haven't shot it yet since the rechamber. From past reports, many H&R .243s won't shoot the 95gr-100gr bullets, so I wouldn't expect the 105gr and bigger bullets to do well either, the 1:10" twist is probably borderline suitable for the longer, heavier bullets, but the only way to find out is shoot em, be sure to let us know!!

Tim