[BryanK]

I have seen it mentioned in other forums that a 3" will function in the 2 3/4 receiver with the "steel shot" barrel with no malfunctions, but yeah, it is the internet. The SAAMI max average pressure ratings for a 2 3/4 shotshell and 3" shotshell are the same (11,500 psi), so if the barrel is chambered for it, it should be good to go. The receiver has to meet those pressure ratings as well, so if the Max pressures are identical why not? On page 13 of the attached .pdf breaks down the pressure ratings for the different shotshell groups (shotshell, rifled slugs, sabot slugs).

Here is a snip from the description of a steel shot barrel for sale from Cheaper than dirt:

Model 1100 Steel Shot Barrels are designed for use with 2.75" or 3" Magnum steel or lead shot shells when used on Magnum receivers and 2.75" or 3" Magnum steel or 2.75" lead shotshells when used on non Magnum receivers

CTD link

While a little pricey, it looks good and will fire 3" steel shot.