Pardon my ignorance, guys, but I have what should be a relatively simple question for physics buffs. I haven't studied any real physics since HS....... Here is the situation: I am performing some .45acp ammunition ballistic tests using a gelatin block. In order for my tests to be valid, I have to calibrate the block, which requires a standard 0.177" bb to be shot into the gel at 590 feet per second (+/- 15 fps) and penetrate 8.5 cm (+/- 1 cm). Easy enough. My issue is that my bb gun only achieves 350 fps. That is roughly 60% the desired velocity. My question is this: Is the desired penetration depth directly proportional? In other words, should I be looking for a penetration depth of 5.04 cm, or does deceleration act on the bb in a non-linear manner causing it to penetrate less than 60%? I appreciate any time you take to answer this and thank you in advance. Have a good one, guys.