RE: will this hurt my bow?
 

OK, so now my question. Is there some reason, besides testosterone, that you can't turn the bow down to 65#. Maybe I've been wrong for 35+ years of shooting compounds, but I have always been under the impression bows were adjustable for a reason.

RE: will this hurt my bow?
 

It comes down to the forces at play. The lighter the arrowyou shoot, the closer you are to dry firing your bow. There's a lot of energy when the sting is released, it needs to have an arrow of sufficiant weight on it to absorb that force, and keep it from destroying you limbs, raiser, and accessories. 5gpp has become the defacto industry standard for minimum grain total arrow weight.

Will shooting this light of an arrow definatly hurt your bow? I don't know, but it's not a risk I'd be willing to take.

Also, I don't know that you'd be shooting anything close to a proper spine if you were to shoot a 325 grain arrow from a 70lb bow. That will have a big impact on arrow flight, all the more so with a broadhead up front.