Not knowing how heavy your arrows are I just calculated your Kinetic energy using a 350 grain and 400 grain arrow weight. The results were 41lbs at 350 and 47lbs at 400.

I don' t believe you are pushing enough kenetic energy to get full penetration with a mechanical head of any kind. They will fly straight and true but your lack of penetration and your sons are evidence enough that you should both be using a head designed for maximium penetration.

It' s sounds like your Thunderheads have been good to you........stick with them.

I am going to say this as politely as I can........A little bit of research on you or your sons part could have prevented 2 lost injured or dead deer. Live deer are not for testing out heads to see if they work.

Couldn' t reply without saying that........I hope you see I am just trying to help you........and the deer