Work in progress
Its a good start but there are a few things that need to be cleaned up:
First biggest thing is the accuracy, just because you didn't kill a chicken in 1 shot(which is impossible till you get the shotgun) doesn't mean your accuracy should go down.
The windows closes way to slow to be of any use you either can kill all the chickens on the way in or on the way out
You get the shot gun by round 5 and then the game lose a lot of its valve because it's just repetition at that point
You might think about being able to upgrade the guns with things like:
Give ten various levels of upgrades to extend the upgrade path of the game
The weapons should behave differently a shotgun is not as accurate as a rifle the game should try reflecting that.