No it's mechanic.. use a softer spring on the prison doors or see where you can adjusted the mechanism. There's also a switch I believe to see if they are open or not.
Regarding strategy Eskaybee.. yes it works the way you say it. Though not every mode has a repetitive shot (tunnel, cdc and arena).
Clearing the prison yard is of choice, you can shoot the arrows or shoot the prison each time for one of the arrows to clear. Shooting the prison is more dangerous for stdm drain risk.
Though with the shot multiplier that can add up to f.e. 5x, dubbele playfield and shooting modes and score big at the right time is really great.
A Multikill goes together with an obtained weapon once you did something to get them.. But if you score good in a mode, you're multikill is worth a lot more and can really ad up to the scoring.
For me weapons vs multikills should need a little more (for example shoot 3 yellow multikill shots to change an obtained flashing weapon towards a solidly lit weapon).