Mike;
My knowledge of the 16ga in a 3" chambering is rather limited. They were listed in old UMC catalogs. I would suppose the only "Special" requirement would have been to have enough Cash for some minimum order. There well could have been some regions where they gained enough popularity that a dealer in the area could afford to stock them, just don't really know. I have never seen one of the original 3" 16ga shells, I only have the gun with that length chamber. It does have a normal length forcing cone for the era in which the gun was built. It is incidently an H grade with twist bbls. I can thus think of no good reason for it to have been re-chambered at a later date.
Sometime in the 1970's I was at a local gun store & a gentleman brought in a Fired Rem SP hull which was a 16ga 3" with markings on it of 3DE 1˝oz 7˝ shot. He had picked it up from the ground in a wooded area where he was as I recall deer hunting. I have no idea what this shell had been fired at, perhaps a grouse but a rather heavy load for that purpose. I presume there was some experimenting with a 3" 16ga loading at that time, but it seems to have never made it to the market place.
