The .22 Spotter had a full magazine, one round chambered, and no other attachments or mod's.
The bug may have been from,

1. Spray painting the gun black.
2. Switching from one weapon to another quickly,
3. accessing the inventory.

After the magazine disappeared off the gun I was able to chamber a single round, this resulted in a loop animation of the character chambering a round, I could not access the inventory or switch items. The only fix was to log out and then back in, this fixed the issue with the missing magazine.