I have just under 20# of H 450 that I used for long range 30-06 loads back when I shot competition and figured it might work well in a 243 WSSM AR with heavier bullets.

Unfortunately, no loading data available on this powder/cartridge combination and Hodgdon declined to comment, so proceeded to calculate a starting point and work up a load from scratch using ladder method (left hand target)

Best group I got was about 3/4" (right hand target) but was stringing vertically and was right at 100% density. I increased the charge .3 gr. and shot another group, resulting in an inch and a half group.




It would seem to me that since vertical stringing usually calls for a bit more powder, and since adding powder did not help, perhaps I am having an ignition problem w/the Fed. 210's and a full case of ball powder.

Have never gone from LR to Mag primers and wondering how much I should cut the charge for starters. Any thoughts on the matter?

Regards,
hm

I go 2 full grains down then work back up.