Howdy
Let's talk chokes for a moment.
There are quite a few different chokes, but for the moment let's limit our discussion to the five most common. Cylinder, Improved Cylinder, Modified, Improved Modified, and Full. In that order, Cylinder is the least restricted and Full is the most restricted. (Actually, there is no restriction with a cylinder bore, there is a complete lack of restriction with a Cylinder barrel, hence the name.) When shot leaves the barrel of a shotgun it has a natural tendency to disperse. So the farther the shot travels, the more it disperses, causing the pattern to spread out. The more a pattern spreads out, the more 'gaps' there are between pellets. A choke squeezes the shot a bit just before it leaves the muzzle. The more choke, the tighter the pattern remains at a given distance.
I have been shooting trap for over twenty years. I learned to shoot with a Full choke with my Dad's old Browning Double Auto back in the late 1960s before interchangeable choke tubes were invented.
These days I usually shoot an old Winchester Model 12 with a built in Full choke. I do have a Beretta Over and Under with screw in chokes, I usually put a Modified choke in the lower barrel.
Just about everyone I know shoots Trap with an Improved Modified choke. A few use a Modified choke, and a few use a Full choke like me.
I tend to agree with your friend, although I would probably be a bit more tactful. Improved Cylinder is really not a very good choke for trap, yes 16 yard trap. By the time you fire, the target is probably about 30 yards away. At that distance, the pattern thrown by an Improved Cylinder choke will probably have a lot of 'holes' in the pattern. You might be right on, but a target could easily slip through the pattern and not be struck by any pellets. Or not struck by enough pellets to break it. Generally speaking, the target has to be struck by a few pellets, not just one, to break.
If I were you, I would use the Modified gun. You will have a slightly denser pattern than you would with the Improved Cylinder gun. More chance of hitting the target with enough pellets to break it.
With my Full choke, I have less room for error, I have to be right on because the pattern has not spread out as much at 30 yards. But the pattern is so dense out about 30 yards that when I am on, I smash them and there is nothing but dust left in the air.