I have to second the idea your better off using SLUGS in a shotgun designed to maximize their use,
when hunting deer a savage bolt action in 12 ga can keep consistent 3" 100 yard groups
with the sabot ammo
(rifled barrel) THIS SAVAGE IS AN EXCELLENT GUN
these bolt action shotguns have rifled bore designed to stabilize slugs YES THERES A LOWER RECOIL 20GA VERSION
if your using buckshot a 10 ga tends to throw noticeably tighter groups in my experience than any 12 ga
and throws 18 OO copper plated pellets into an effective tight group out to at least 40 yards in my ithaca road blocker
https://www.midwayusa.com/product/1002079456
the Ithaca 10 ga road blocker holds two in the magazine and one in the chamber , the legal max for some areas.
its very effective, inside 40 yards , Ive used one for decades.
if you want a reasonably consistent way to judge at what range double OO buck shot will be effective on deer or hogs,
place a single sheet of typing paper horizontally at 20 yards and fire a shot at it, if you have at least 5-6 holes someplace on the paper you can be reasonably confident that it's effective, now back off 5 yards and repeat, , back off 5 yards after each success, this extended range and test,
after each successful buckshot shells are shot and tested, is a reasonable test that places those 5-6 holes in the paper.
yes, you'll occasionally see guys drop deer at longer ranges, but far more will result in long trailing jobs or lost wounded deer in my experience,
you're still in effective range, once you reach a range where less than 5-6 holes in that sheet of paper are consistently there... your past the effective range,
now obviously a 9 pellet 2 3/4" 12 ga buckshot load is at a distinct disadvantage to a 12 pellet 3" shell or a 3.5" 10 ga with 18 pellets
and why I prefer a 10 ga ithaca if I hunt dense cover in fla swamps,for hogs and deer.
and yes different shotguns pattern loads differently, but in our hunt club this test has consistently shown to be valid in results seen on game.
yeah, you'll rapidly find that your buckshot loaded shotgun is only effective at a limited range thats more than likely LESS than you might have envisioned!