5/16 has less shaft drag than 11/32 so it would give better penetration; but 5/16 doesn't come in 65-70 spine and doesn't weigh 500 grains either. Anybody footing them with hardwood to achieve a 5/16 cedar shaft with 65-70 spine and 500 grains shaft weight?
I don't understand spine dynamics very well, but I don't think footing the cedars with hardwood would increase the spine. I would think it may actually weaken the spine a bit since more weight would be added to the front 1/4 or so of the shaft. Interesting question though. Maybe someone more knowledgeable will chime in.
I don't think footing would help with the spine. I saw some 5/16" ipe (Brazilian rosewood) shafts offered recently that were that heavy, but I can't remember where it was. Maybe this will jog someone's memory, and they can tell you where to look.
You might try hickory shafts, also. I have some 60# 5/16 hickory arrows that weigh 660 grains at 27 1/2", and I'm sure they could be had a little stiffer than that.
Luck!
Bjorn, I have some that are footed with purple heart and some with cocobolo but they are 11/32". They weigh about 500 grains full length and spine 80-85#. The purple heart is a bit lighter. The few I've made up I made them 5/16" in the front slowly tapering to 11/32" at 2/3rds of the shaft, then taper to 5/16" at the nock. With that taper they still spine 75-80. The "rules" of how weight changes spine go out the window when you are dealing with footings and tapers. Most footings weigh more but extending down into the shaft, they stiffen it...net effect of the increased weight up front is zero. Same when internally footing carbons....O.L.
OL; the ones you made tapering from 5/16 to 11/32 and back to 5/16 how long was the footed section and how'd they fly?
Thanks,
Bjorn