This makes it difficult to switch e.g. from heavy to light oil (as I had just done because I was running out of heavy all the time, causing Fun) since it won't accept the light oil if there is still a bit of heavy oil left, but it won't deplete the heavy oil since it's not enough to fire. Workaround is deleting and re-placing the turret, but that's annoying.
Solution would be to have the last legitimate shot also take the extra fractional shot, or to allow a shot anyway if oil is between zero and minimum.
