Been there/done that Bronko. The spin from the rifling screws up the pattern big time. Useful for rats out to twenty feet with #8 shot. If you can get what we've always called ratshot (#12) try wingshooting dragonflies. If they're close enough, you'll never miss (the blast takes them down).

28gauge will indeed go down most 50s. Been there done that.

OK, how about a .50 cal. sabot cup AND appropriate 'patching' (inside of cup) to accommodate said ball/round size?
Realizing the 'fit' must be tight, to almost difficult, to ram home for proper transfer of barrel twist upon discharge of powder. My thinking, today was...if I did use this "system"' the 'patches' may slip within the cup; thus failing to impart the needed twist for stabilization and accuracy.
Here's what I believe is needed. Somebody needs to develop interlocking sabot cups, so that we can adjust for seasons without having to, own/buy, multiple barrels or multiple rifles. Not that this a is bad thing.
I, personally, would try to develop this if I had the time or the abiltiy; neither of which I have.
littlekid

You are one smart littlekid, if I was as smart as you I'd go to Grandpa and hit him up for some cash and get the ML you need, Im sure with your smarts you can do it! LOL!
(BP) p.s. how little or should I say how OLD are you?

BP,
Not sure how to react to your post. Smart's...not quite sure (don't ask my wife; according to her, I'm an IDIOT until something needs fixin'), size/age...I'm 37 and stand 5'3" @ 145 lbs and ex-collegiate wrestler (D-1, with aspirations of the Olympics until injuries; have beaten 2 qualifiers though).
The 'nickname' littlekid was bestowed on me in college during my fraternity days.
As for asking grandpa for money....they're both DEAD!
MONEY...I'm a highschool teacher/coach that NEEDS the quiet time in the woods/water to remain SANE.
littlekid

Dang...I'd change the name...

Honestly, what you are talking about has been tried off and on for 300 years...Drop the powder charge down to 40-50 grains, adjust for 25 yards and pop the squirrels in the head...I've done it with a .40, .50 and .54 since the 70s...Just be careful of your backstop...