He's gun savvy enough to not go loading the gun right here and now and testing it out, because that's dangerous. And why waste these holy rounds on target practice? If nothing else, he'll test them out with normal rounds when he gets home. Also, show them off to all his Rotten buddies at how incredibly cool they are. Some of them are still afraid of the Nexus but now he can show them the amazing things that can come from it!

"Awright, lesse what else we got here." The gun is put carefully back in its case again, same for the ammo, before this latest box is opened up as well.