Spine??????
 

I have been shooting Beman ICS hunter 400 shafts for a while now. These arrows are being shot out of a Legacy. My draw length is 29" and the arrows are 28" . My bow was set on 64 lbs. I had 4 inch feathers and 100 gr. feild points. Put perfect bullet holes through paper with the fletchings on and with a bareshaft.

Here is where the problems started. In order to obtain a little more speed I turned the poundage up to 72 ( the limbs are bottomed out). In order to compensate for the extra draw weight I went to an 80 gr point ( for the spine ). When I started shooting my groups were not that good. I was no longer able to shoot 4" groups at 40 yards. I decided to shoot it through the paper again. With the fletchings I got a slight left tear but I mean very slight. I then shot a bare shaft.........WHEW.... bad left tear. Immediately I thought my spine was too weak so I turned down the poundage which fixed the problem. Now most people would have stopped there and been happy but not me.

I checked the Beman web site to see if I had the correct arrow. The specified arrow for a hard cam, 72 lbs draw weight, and a 28" arrow is a Beman ICS Hunter 400. If this is the case, why the bad left tear? Are these charts not specific enough about the point weight being used? I don' t understand how a carbon arrow can be so underspined when the manufacturer specifies that arrow size.

Any thoughs?
Should I use an ICSH 340?

RE: Spine??????
 

If I remember right, the threshold area is right around 70# for the ICS. At that length and weight it may be a good idea to go with 340' s.

I shoot at 78 pounds and 29" draw. My arrows are only 27" long though. I' m using 340' s with my setup.

Decreasing point weight should help to increase spine on the already existing arrow too.

RE: Spine??????
 

Not sure how the two bows would compare for spine, I shoot a BKII, 29 inches at 71lbs and arrows cut to 27 5/8 so we have a similar set up. I shot both the 400 and 340 before buying and my bow shot the 340' s much better. If you have a pro shop they should have some you can shoot and see what your bow likes better.

RE: Spine??????
 

Well,

I made a decision. I bought some new arrows altogether. I bought the CXL350' s made by carbon express. The finished weight with 2.6" plastic vanes and the adjustable nibs (mine weight 80 grs) are 332 grs.

I am going to adjust the draw weight to the spine. This seems less expensive then my past ventures which has left me with alot of over and underspined arrows and alot less cash :D:D

RE: Spine??????
 

BS73,

Don' t forget that feathers make for a weaker arrow spine as do heavy inserts like the ICSH and Easton CarbonAeros use. Most arrow spine charts assume the user is going to be using vanes.

Now that being said...

Out of my Legacy w/ 28.5" cam 70 pounds, with a 28" cut length, an ACC 3-49 w/ 100 grain point and feathers was the optimal spine. The 3-49 is a touch stiffer (.390) and also has a lighter insert so, It' s possible with your slightly weaker shaft and 1/2" more draw length that it was too much energy being generated when you cranked it up to 70 pounds.

RE: Spine??????
 

I just ran your arrow and bow through ' The Archery Programs' spine graph and show even at 64 pounds you are just slightly weak. As long as you are still in the yellow I have found good flight. When you hit red in the weak tuning can be a nightmare!

The #1 left is 72 pounds (off the chart)
The #1 right is 64 pounds. Should tune ok but could be better.