I'm not really sure how that could help.
If JB's DNA was found on the bullets, then he could say he had handled when they were purchased, or at some point since then.
If his DNA wasn't found, then as you say he could have worn gloves.
Or maybe the bullets were just tipped out and not touched at all, therefore no DNA traceable.
In any event, do they even still exist?
I am not sure if they do still exist . Mike did have a list of everything that was destroyed.
There are lots of ifs and buts - perhaps JB did not buy the ammunition? Did AP leave his ammunition there?
Thinking about it if they DNA tested the silencer, if the casings were available you think they would have done them at the same time?