Tire valve stem caps, shaped as bullets! Pretty cool.
http://www.acmejeepparts.com/products/15156_100.htm
But, they were only on 9mm and I'm a 45acp guy.
It didn't look hard to reproduce, so I gave it a shot (excuse the pun).
Fun Project - Bullet Caps!
I pulled the caps from the Jeep. I was missing two of them so I went to O'Reilly Auto Parts and purchased a new set of 4 for $1.00. They offer both a long and short cap. Mine were the longer ones.
I dug out 5 clean .45acp brass from my reloading bench and cleaned them well using a degreaser and hot water.
I used two drops of Palmolive dishwashing liquid, hot water, and an empty gatorade bottle as a shaker.
There was still some burnt powder residue inside so I reamed it with a paper towel. Then, hair dryer to make sure all the moisture was evaporated.
I had two types of adhesive laying around the house. Gorilla gel (superglue) and Gorilla epoxy. Not knowing which would work best, I did one of each as a test.
I filled the 45acp casing 1/3 with the adhesive. Then, I slowly pressed the valve stem cap in place. I was careful to wipe off the excess and not allow any to fall into the inside of the cap.
8 hours later, both held strong. After the 24 hour curing time, I think either would be rock solid.
Cost: $1.09 + stuff I already had.