Why is my friend's game different on my computer?

My friend and I are developing a first person shooter, and when he sends me the .exe a lot of things are different. For example, when I set my graphics settings to “Fastest” the fire rate of an automatic rifle is increased dramatically. Is there any way to easily adjust the program so that little things like fire rate are not adjusted by graphics quality.

Is there something involving the power of my computer, or my graphics card that we are just over looking?

You’ve made your code framerate-dependent by not using Time.deltaTime appropriately.