I never thought of that before. You’re right....does not compute.
Some episodes showed him putting the bullet in as a part of the script...in some it went off afterwards. Some I can think of are:
Barney's First Car
The Big House
The Perfect Female
Can anybody think of others?
Early in The Shoplifters, Barney loads his bullet when he’s checking Weavers at night.
In Convicts at Large, the bullet was in his shirt pocket, but this time Big Maude loaded it up.