So your shooting a 300 - 310 grn arrow then correct? That's about what I come up with for weight at 280 fps and that KE. Just be sure that's not under what the bow is rated for. Your probably ok unless you shoot 70 lbs and 30 inches of draw. Your probably on the line though.

And are you saying you were shooting aluminums before, then switched to light carbons and you lost 10 ft/lbs of KE. You didn't change anything else in your set up? That's alot of KE to lose by changing arrows I think. Usually it's only a few ft/lbs because your speed varies in direct proportion to your weight and it sort of equals out in the end. Your momentum would go down, but I wouldn't think your ke would not go down that much.

I would also check to be sure your arrows are spined correctly for the bow you are using. Not that you can't get get carbons that light, but most of the popular brands are not that light unless you get the arrows for lighter set ups, like I shoot (low poundage, short draw). And you wouldn't be getting 280 fps if that were the case. Now if you bought some of the more expensive 3-D type arrows they are pretty light.

At any rate, that's plenty of ke to take deer with. Just make sure your arrows are the right spine, the bow is tuned well with broad heads, and you pick a good sharp head. And as always, concentrate on shot placement.

Good luck,
Paul