Are you using ICS type arrows? and just fastening a layer of aluminum {arrow?} over top. ...Just a waste of time IMO. If that's the case, if you hit a hard object, you will still split the end of the shaft.... The HIT insert will still be pushed back and the end of the arrow WILL split. Try to find an aluminum shaft that will fit nicely over the carbon shaft that that you are using, taper the back edge of the footing and use the insert that goes with it to bottom out to the carbon shaft, JB weld the whole works and make sure it spins true,....let set completely and dry. Aluminum shafts are marked by dia and wall thickness....eg. 1916 are 19/64 OD,..and .016 wall thickness. So,..19/64 = .304 - {2x.016}= .032
...= .272"..
You have to figure out which aluminum shaft best fits your carbon shaft OD. ...Lloyd