Hey fellas. Been away from archery for a few years. Swamp Jr. has a Sci project and decided to do it on arrow penetration upon an object. His hypothesis was that a heavier arrow would penetrate deeper into an object based on KE.

Well the test went as follows: 10 yard shot shooting into block target using a 85 grain tip, 100 grain tip, and 125 grain tip. The same arrow (Easton Acc 3-60's) and bow was used for all tests and the same spot on the target was hit on all shots.

The results:
85 gr 3 shot average: 28.75 cm of penetration of the target
100 gr 3 shot average: 32.5 cm of penetration of the target
125 gr 3 shot average: 30.5 cm of penetration of the target

Based on our theory, the 125 grain tip should have penetrated the target the most, but did not. I know the logical thing to do is to shoot thru a chronograph and get fps and weight of arrow to figure KE. But the local shop is closed today and the project is due tomorrow [:-].

Can ya'll give me some reasons why our theory did not hold true?