Some 1100's could fire the 3" shells. This is what Remington has to say.
he gas cylinders are welded in slightly different locations. This is partly because the 11-87 has a longer magazine tube. The 11-87 also has 2 gas orifice holes. Only the 2-3/4 inch chambered version of the 1100 will have two. The magnum 1100 barrel has only one.
The 1100 can shoot only 2 3/4" or 3" shells depending on the barrel installed, and with the 1187 models with magnum barrels can shoot both 2 3/4" and 3" shells. To accomplish this, two additional holes are drilled in the top/front of the gas cylinder, and covered with a tempered steel spring. There is a relief cut made into the gas cylinder to accommodate the spring. The Model 1100 gas cylinder will not have the relief cut or the spring.
So, as long as he has the right barrel, he can shoot 3" shells. Actually with that barrel he can only shoot 3" shells. At least that is how I read it.Becausewith the 3" barrel it will not cycle the action properly when firing 2 3/4" shells.As for shooting lead, fire away. The steel shot stamping indicates it is ok for shooting the harder steel shot. Good luck.