It's too early for your friend to start worrying, first a few questions.
What makes you think it has short chambers? How do you know it's a Sweet Sixteen? The name was not engraved on the receivers till '48.
The safety in the front of the trigger guard is not evidence of short chambers, that safety was in production until late 1951 and all the 2 3/4" guns from the end of the war till then have them.
The "solid" rib also tells you nothing about the chamber length.
In addition "Pre-war" A5 16's had 2 9/16" chamber but many of them were modified to cycle 2 3/4". If it is a short chambered gun you need to know how to tell if it was modified. Do you know how to tell?
Post the serial number and the numbers from the proof marks (16-65) or (16-70) and I'll help you figure out what this gun is.
Jeff
