Winchester Model 1200 Riot - Question on Tube Capacity

[Bedfordtec]

I have a Winchester Model 1200 Riot gun with the standard tube (not extended) . It is chambered for 2 and 3/4 shells. All the references say that the capacity is 4 + 1. However, i am able to load 5 dummy metal rounds into the tube with the last one just clicking into place with no extra room. Gun cycles just fine with the 5 rounds in the tube. Could the 4 +1 refer to 3 inch rounds? Anyone have a similar tube? Thanks.