Yeah, I've got 4 potato cannons and 2 of them share 2 barrels. Ive got a 4in chamber, 3 in barrel combustion. A 4 in chamber 2 in barrel, or 2 1/2 in barrel(for tennis balls) combustion, it uses a battery grill ignotor jacked up with 18 volts, or a tazor. A 3in chamber, 2 or 2 1/2in barrel pneumatic. And a 2in chamber 1/2 in barrel(far double A batteries, apple cores, etc) pneumatic. They are all so much fun. I was able to shoot a tennis ball about 1/2 mile to 3/4 mile away from my house to the high school football field. And I bent a double A battery in half shooting it at a cinder block wall. So much fun. Thanks for the measurement. Take some pictures of your bushings installed. I love seeing the Red bushings on trucks.