[arcticap]

At least by using Pyrodex it's not explosive when it's not contained.
I've loaded and ignited Pyrodex in a barrel without a ball and I could hardly tell it was going off when it's not contained.
All one would need to do is to wait a number of seconds from the time that the last shot was fired before reloading, very similar to being just like with a misfire.
That's just standard practice that everyone should be made aware of and reminded about.
But by the time that he puts his gun down and he reloads his syringe the time limit would be up.
Wear eye protection and remember that the syringe is an open volume of Pryodex and not a closed container of black powder.