Good morning, gentlemen.... Here is what you have been waiting for.... Here are the contest questions and the answers (in red):

You have been reading Bob Sterne’s articles, particularly those at Hard Air Magazine, and now you want to put that information to use. You want to build your own custom PCP, and need to figure out some important details. Your goal is to end up with a regulated PCP, fed by an onboard 500 cc bottle that can be filled to 300 bar. You want a .257 cal that shoots 70 gr. slugs at 950 fps, from a 24” barrel. You need the answers to the following questions (all answers to be in whole numbers, no decimals):

1. What will be the FPE at the muzzle?

FPE = 950 x 950 x 70 / 450240 = 140 FPE.2. To achieve 90% of Bob’s “lofty goal” FPE calculation, what setpoint pressure (in psi) do you need for the regulator?

Maximum theoretical FPE is Force (lbs.) x Distance (ft.)… My “lofty goal” is half of that, so:

FPE goal = 0.257 x 0.257 x PI/4 x Pressure x 24 / 12 / 2 = 0.05185 x Pressure…. Therefore:

Pressure = FPE / 0.05185 = 140 / 0.05185 = 2700 psi

To reach 90% of that, you need to start with Pressure = 2700 / 0.90 = 3000 psi. 3. What is the recommended plenum size (in cc) that Bob would recommend?

I recommend a plenum of 1 cc per FPE, so that would be 140 cc.4. If you achieve an efficiency of 1.00 FPE/CI, how many shots should you get before the pressure falls below the setpoint?

Fill pressure = 300 bar, and Setpoint pressure = 3000 psi / 14.5 = 207 bar

Pressure drop = 300 - 207 = 93 bar. Reservoir volume = 500 cc / 16.4 = 30.5 CI

Total air available in “standard CI” = 93 x 30.5 = 2837 CI

Efficiency is 1.00 FPE/CI, so 140 FPE requires 140 CI of air per shot

Number of shots = 2837 / 140 = 20 shots. Several of you got the correct answers for questions 1 and 3.... One of you additionally got the correct answer for question #4, and his answer on question # 2 was within less than a third of a percent of the correct value.... Therefore, the FX Radar Chronograph is awarded to (drum roll please)….

**Loren**....

Bob

PS … Honourable mention goes to FL Rat Hunter, who also got 3 correct answers, but entered after the midnight deadline....