M230 Chain Gun
Finally! The right diameter, but the wrong length and gun. That's close enough for me. Chain guns use lightweight 30x113mm ammo in cases 4.449" long. This is a slice of GAU-8 Avenger barrel from an A-10. They use 30×173mm ammo in cases 6.811" long. That's 60mm, 2.362", longer, and the rounds are about the size of a Coke bottle. My friend who was an Air Force sergeant in charge of loading A-10s, including in Iraq and and Afghanistan, gave it to me. After each barrel has fired 12,000 rounds (or whatever) has to be pulled out and replaced. The old barrels and then sliced of in 2 or 3(?) places and examined for wear and cracks, etc. If a barrel doesn't have that many rounds through it yet but will before the next mission is over, they replace it.
One day out of the blue I gave him a custom embroidered key chain with metal grommet from 1800nametape.com. I ordered it when I got some embroidered name tapes with Velcro backing made for myself. You choose 4, 5 or 6 inch length, color of the cloth tape, color of the thread, border color, upper and lower case or all upper case, font, letter size, front text and back text. But no matter what length and what letter size you choose, you're limited to 16 characters and spaces. I made it as close as I could to a REMOVE BEFORE FLIGHT red safety ribbon used when an aircraft is on the ground. They're used indicate that a device, such as a protective cover or a pin to prevent the movement of mechanical parts, which may include a pitot tube cover or a control lock has to be removed before flight. Because of the max characters allowed It ended up being REMOVE B4 FLIGHT on both sides, in the correct colors. I took the standard metal key ring off and replaced it with an M67 hand grenade ring I picked up in the army. Then I drilled a hole in the corner of a red UTG frearm chamber safety flag and put it on the ring. He seemed genuinely pleased, and definitely surprised, to be gifted it for no apparent reason. I didn't want or expect anything in return, but was pleasantly surprised when he later gave me the slice of an A-10 barrel. He has an Air Force Maintenance badge as seen on this Milspin hat embroidered on the left chest pocket of his old uniforms. One woman who embroidered his shirt sewed right through the pocket making it completely useless, instead of ripping the seams down the sides, embroidering the flap and sewing the pocket back on. Good help is hard to find.
https://store.1800nametape.com/keychains.aspx https://en.wikipedia.org/wiki/Remove_before_flight#