I'm not exactly sure what 16pt is, but a conversion chart tells me it is around 340gsm.
On our old KM6500 we used to run a lot of 300gsm silk, mostly simplex, but also duplex (officially out of spec). We would also run 350gsm silk simplex. With the out of spec stock we didn't find jams to be a problem, but the stiffness of some heavier boards could sometimes cause the tail edge to "whip" and not image cleanly. This was more likely to be seen with heavy uncoateds. We would also run 300gsm C1S, which is about 380mic, without problems.
On our present KM8000 it will run 300gsm duplex all day long. 350gsm is in spec for simplex, but will also run duplex without problems. We have tried pushing the machine towards its limits and find we can just about run 350gsm uncoated, which is nearly 420mic, and 330gsm C1S, which is also around 420mic. With the latter, we were just starting to see evidence of "whip", but at the extremity of the sheet, so in the bleed area of 8-up postcards.
Again our conclusion is that it isn't just the weight, or even the thickness, of a board which determines how well it runs, but also factors such as stiffness. Pretty well all these heavier boards are grain short, which help. My guess is that long grain at these weights would probably be difficult to run.