I did an informal field test a few days ago comparing 2 3/4" #4 buck to 2 3/4" #0 (not 00) buck. The victims were two old laptop computers that my wife asked me to "decommission". Range was 20'. Shoulder fired, aimed from my Ithaca 37 Deersĺayer, 20" cylinder bore barrel. Result: two very dead laptops, but the 27 pellets of #4 buck was noticeably more devastating due to the pattern more completely covering the target vs a more centralized pattern. Actual effectuve difference: Nil.
I've shot a lot of 3" stuff in years gone by when I duck hunted a lot (lived in the East Arkansas delta for 6 years, and duck hunted 3-4 days a week). For waterfowl, I think the difference is real, although shotshell and pattern technology had made great advances since I was duck hunting in the 90s. Nowdays, the only thing I use 3" for is turkey, and probably not necessary then. I will also carry my Mossberg 835 with 3" Dead Coyote loads (size T shot) when predator calling at times. My favorite all around load for small to medium game (not dove/quail wingshooting) is a 2 3/4" short Magnum, 1 1/4 Oz. of #5s. Pattern is really good out of my Ithaca 37 with 30" full choke barrel. I patterned it just a couple of weeks ago, and it would be a reliable 40 yard turkey killer.
I've shot some 3.5" / 2 Oz. stuff out of that Mossberg, turkey loads and I had one box of 3.5" Dead Coyote. Nope. Very unpleasant to shoot (although you wouldn't notice so much if shooting at a longbeard). I am not that mad at turkeys. I remember patterning those, set up a paper at 40 yards, rested over the corner of the bed of my pickup.
Boom! Yikes, that hurt!
Couldn't be that bad, I must not have been holding it tight or something. Tried again.
Boom!
Yep, it was that bad.
If I thought I needed 3.5" power, I would for sure get myself a gas-operated autoloader, not a pump where you take the full force of the recoil.