I wish my 243's liked the gamekings, so I don't have any info on that bullet. Both of my 243 rifles seem to like flat based 100gr bullets better than the boat-tails. I believe a 1-8 twist would work much better on the long 100gr. boat-tails. Of course nobody makes a factory rifle with that twist. I've settled on 100gr speer grandslams for deer,very accurate, penetrates and expands very well. I will shoot deer at any angle with these bullets and not worry about not having a exit, it will be there. With 100gr bullets I've had better luck with slower powder then varget(I use varget with 70gr bullets)and imr 4064. I've had good luck with h-4831 and 100gr bullets. You might want to try 85gr gamekings if you can't get a 100gr bullet to handle good, lots of people brag on them for deer. Wish I could have answered your question,just thought I'd share my experiences with you. Dave