I have two 65mm chambered 16s. One of them weighs 5# 11 and I shoot reloaded light 2-5/8" 7/8 ounce and light 1 ounce factory loads in the gun. I don't see any difference in the fired shell relative to another gun with factory 2-3/4" chambers. I am considering lengthening the chambers in at least one of these so that I can feel better about using 1-1/8 ounce loads for pheasant.

These guns were purchased used and I'll bet they have been used a fair amount with 2-3/4" loads. Not everyone reloads or buys RSTs.