I think they were given the clear mags (all three had them BTW) because it was a live fire, no blanks, so the safety crew could visualy inspect.
I think the SEAL got ripped off. I think the guy that did the weapon inspection at the end was full of shit when he said "This weapon ruined." (or close to that). Or that "He wasn't seating the mag fully". From what I saw, the seal slapped the mag in fully SEVERAL times. Or when the weapon inspector opened up upper and lower and wiped his finger and said, "Look, it is filthly with brass shavings".
On hind sight, I would have hand fed a single round in at a time if it were me. Lock back bolt, point down, drop one round in, release bolt, fire. At least that way would have been able to try for the targets.
[edit]
I take back the Live fire, read the above web site. Now I don't understand why they didn't use live rounds? When they were given the weapons to test fire, they were shooting at plywood and punching holes. Wasn't that using live rounds? If so, why did they change to simunitions?