Proton Gun

The Proton Gun is the 19th gun available, unlocked at level 28 and costs $18.99. It was added during the 1.6 update and is a Ghostbusters item. It boasts the largest clip available, 200 bullets, with each bullet able to slow down your opponent by reducing his agility to 0.5, such that he is easier to hit and won't have enough speed to run away. The agility provided is moderate, but the damage, range and accuracy are high, ensuring quick, long-range kills.

With a high price of $18.99, this weapon is good, but not near as good as the Noisy Cricket, so you may want to consider getting the Noisy Cricket instead of the Proton Gun.

Strategy
This is overall a good long range weapon, so use it to your advantage. Position yourself at a vantage point, and pick out a target. Once you hit him, he won't be fast enough to run away, and assuming no one steals your kill, you would have taken him out without giving him any chance of running away.

Excersise a bit more caution at close range, for although the Proton Gun slows their speed, it does not slow their gun's fire rate. So if a blunderbuss user is coming in for the kill slowly, BACK away, or you will risk having a nasty surprise.