confused greenhorn penetration ?

[mainebuck]

Ok, I have recently gotten into traditional archery and have been reading about the recommended 10 grains per pound of draw weight for arrows and I am somewhat confused.

Up until this point I have been shooting 350 grain carbon arrows(that includes a 100 grain broadhead.)  After reading reading A LOT from you guys in here about appropriate weight of arrows for penetration I got 505 grain carbon arrows(that includes a 125 grain broadhead)

Heres my dilemma.  I shoot these arrows back to back into a foam target.  The 505 should penetrate better right even though it is flying quite a bit slower?  However, at a distance of about 20 yards the 350 grain arrow is penetrating more and flying quite a bit faster.  Does it have more kinetic energy even though it weighs less.  The heavier arrow seems like it packs less of a punch than the light one to me.  Will the penetration into the target translate into a deer?
Thanks

[Bjorn]

Assuming both arrows are properly tuned to the bow the heavier arrow will have more KE ,despite being slower in flight, and will penetrate deeper given the same shot placement.
Please describe your bow and how did you select the spine weight for both set ups?

[DRR324]

May sound dumb here, but, if the target is a foam type (mackenzie) the larger arrow will have more friction and thus stopping penetration quicker.  I wouldn't think the difference is a lot, but I have noticed the same when I shoot my lighter carbons compared to my cedars- from the same bow.  The wood never gets in as far as the carbon- I figured it was due to friction of the target.  Are my assumptions wrong? I'm sure someone with more knowledge would know the correct answer.
Dave

[aromakr]

Dave:
Your difference in penetration is due to several factors. YOur wood shafts will be a larger diameter than the carbons and the finish on a wood shaft will provide a greater resistance due to friction than the carbons surface.
Jeff:
Foam is not a good media to judge penetration in, also you heavier arrow may not be tuned to your setup as well, any side to side movement will reduce penetration as well as different point designs. Or arrows hitting a soft spot and others hitting a new spot in the foam where resistance is greater.
I would suggest you read Dr.Asby's report on this site. Its very long and detailed, however I think it will answer you questions.
Kenetic energy is a very poor indication of penatration, use momentum much more meaningful
Bob

[Arrow4Christ]

Your 350 grain arrows are flying better, plus carbon arrows penetrate better. I would bet money that is the case. The heavier arrow will have slightly more Kinetic Energy, but I'd rather have the light arrow flying perfectly straight than the heavy one with even a slight amount of mistune!
Craig

[ChuckC]

Remember guys..we have the measure of kinetic energy and the measure of momentum.  Two similar but different things.  One favors fast, one favors heavy.  There are a TON of factors that influence penetration.  some include speed, weight, shape, thickness of shaft compared to the broadhead, the shape of the broadhead, the sharpness of the broadhead, the texture (slickness) of the shaft and the broadhead, the perfect flight of the arrow (or not) the substrate that is being penetrated, the angle of penetration, any movement of the substrate....heck probably the color of the arrow too, who knows.

One major point.....on most deer sized critters, unless you hit heavy bone, penetration is PROBABLY gonna be adequate with most hunting rigs if your arrows are flying well.
ChuckC