I have a new PCH that should be here in a few weeks... It should be anywhere from 48- 52 lbs at my 28" draw..  (I ordered a 50#er +/- 2 #s). I was wondering what size aluminum I should get or do I need to wait for the exact known lbs. I will be shooting  a 125 gr tip, wrap, 3 shield cut 5".. I have an arrow saw , so I can play around with the lengths if needed. Are aluuminums the same as carbon as for as the shorter you cut them, the stiffer thay get?? I would like to stay from 29-31 on length.. Thanks ahead for the replies..

My PCH is 47 lbs at 28" and I shoot 1916's with 175 grs. up front.  You might try 2016's also.

I would recommend 2016 or 2018s depending on how long you cut them. Yes, Alums are like carbons and woods for that matter. They all get stiffer the shorter you cut them. Hope this helps.

Cnorth, by no means an expert. Been shooting trad for 3 seasons now but have only used aluminum. Aluminums tend to have a wide range of weights the spines work for. Are you familiar with the stu miller calculator? You should check it out. You will need all you bow specs and exact draw length for the best calculation. It is also very important to find out in your bow is cut passed center and if so by how much. On another note: I shoot a predator hunter recurve 46@28 and a 50@28 bear takedown. I shoot 2016s cut to 29.5, I draw 27.5-27, 3 -4 inch feathers with 125 heads. Arrows fly great out of both bows. Oh yeah, I shoot split finger. Good luck.

Thanks all for the response so for but I have another question.. I understand on carbon how they are determine on spine such as 300 and 400 etc.... How do you go about reading them for aluminum?  Are the 2016 or 2018 stiffer..

Eastons chart shows the spine ratings. 2016s are .500 2117 are .400 2315 are .340. And the others fit in between. 2018s are stiffer than the 2016.

read alum arrows so:
2016
20/64-inch diameter
16/1000-inch wall thickness
increase in diameter or wall thickness increases spine/stiffness
decrease in length increases spine/stiffness

yes. the first 2 numbers are the diameter and the last 2 are wall thickness. If you have a 28" draw but dont want an arrow from 29-31, Im not quite sure how your gonna pull that off. If you draw 28, I would think the shortest your arrow could be would be like 29 1/4 or so.

Like Wingbow said, first two digits are diameter and second two digits are wall thickness.  So my 2114s are 21/64" in diameter and the thickness of the aluminum is 14/1000".  I used to shoot 2114s from 45# and 50# bows with great results.

I have a chart that lists all of the aluminum shafts from weakest to stiffest spine (Word document).  PM me if you want me to e-mail it to you.

The hunting arrow selection chart from Easton lists the relative spine weights for carbon and aluminum so you can have some sense on how spines vary between common arrow sizes.  See attached link:

http://eastonarchery.com/uploads/files/51_hunt-sel-chart.pdf

thanks all for the replies