So, what are your goals? more penetration and/or more recoil? I can understand 3" in Waterfowling...longer range, better shot pattern density, etc. But, what, exactly will the 41 pellets of #4 buck do that a standard load won't?
A shotgun is always and forever a short-range SD weapon, except for slugs and sabots, which are an entirely different story, and they do
not lend themselves to much practice!
Whatever can be stuffed into a standard 2 3/4 " shell did excellent work for decades, and despite being "old technology", still works about as well as anything.
Why chance a jam when the zombies are coming thick and fast, and your AR has jammed (Custom loads, you know!)and you have two sizes of ammo, and try to stuff 5 3" shells into your shotgun, instead of 4 3" and just
one 3 3/4, and then...what? Reach for your Desert Eagle, and continue the dance?
When TEOTWAWKI happens,the time for ballistic proctology is over, and prior, a goodly number of reliable "standard" loads should be found and stored.
Until then, it sure is fun to mess around...uhmmm...experiment, isn't it?