If he missed the barrel lug he won't be able to get the slide all the way on and probably won't be able to get it off without Gregs' technique thru the mag well or thru the back of the slide.
I had to do a couple co workers years ago, Greg as usual saved the day in getting them back on track. (and made me look good too, not an easy thing).
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."