wood arrow spine

[Jim Wright]

I'd like to hear some thoughts concerning what the rate of spine change should be when going up (or down) in point weight on wooden arrows. For example if you shot a 50lb @29" Hill style longbow with 50-54 lb. spine, 30" long, 125 gr. point arrows, total weight 550 grs. and you wanted to go up to 175 or even 225 grain points keeping  total weight the same, how much stiffer spined shafts would you need?
  Common wisdom seems to be 5 pound spine change for each 25 grains of point weight change but Im beginning to wonder.

[Orion]

That's about right for the second and subsequent 25 grains increase(s).  I find that I can go up the first 25 grains without any change in spine. It's hard to go up in spine weight without also going up in shaft weight.  Heavier spines are usually associated with heavier physical weights. Have a little leeway, but not much.

[Fletcher]

Spine increase needs seem to vary with bow weight and depth of cut, but you are pretty close to my GN Critter Gitter.  I need about 1 lb for each 7-8 grains of point weight up to about 200 gr point.  The rate seems to drop off a good bit after that.  For the 175's, that is about 7 lb spine, about 10-12 lb for the 225's.  I think you would be safe with a 10 lb jump for either head.

Shaft weight to keep your 550 gr. total is gonna be another question.  I think Sitka Spruce is gonna be your best bet.