RE: Low LB Penetration?
A good, solid, sharp head such as a Razor Trick will penetrate great out of a low poundage bow. While not absolutely necessary I'd stick with the cut on contact type head.
I have seen several deer shot with 35# to 40# setups and get acomplete passthrough. Kat shot her 1st deer at 33 yards with a 85 grain Slick Trick pushed by only 37# and got a complete passthrough.
The most important thing is at least a medium weight arrow with adequate FOC, sharp broadhead, and an accurately placed shot.
Dan