tubing in arrows for weight?

[zmeister]

Hi all,

I was told that adding fish tank air line tubing to carbon shafts will increase the weight without affecting the spine.  I have Gold Tips 55-75's, 30 inches with 165gr point.  They are the cheaper expedition shafts...8.3gpi.  They bare shaft tune fine, but when I put the tubing in, they are shooting way weak.  I'm shooting a Black Widow PSA 60" 55@28" and my draw length is around 28-3/4"  Any ideas what's going on?

Thanks,
Z