Indeed. A 3/4oz or 7/8oz load of buck. Currently the Winchester Defender is 20-pellets of plated #3 at 1145fps. That's about a 1-ounce load of buckshot. A tad bit lighter than a 9-pellet 00 load, but not so much you'd actually notice.
That's what's great about that Spartan load of #1 (that's SA2000 - if anyone finds some for sale, I need all of it you can buy). It's 9-pellets (I misremembered when I said 8-pellets) of #1 or about .84oz shot load at 1200fps that's about 1/3rd of an ounce lighter than 9-pellet 00. That makes it a true "20-gauge load" of buck.
At least there is a good slug load. Brennekke THD, 308gr (.70 oz) @ 1200fps.
I literally had a dream last night that I SBSed one of my 20ga 870s and it was good.
Matt Haught
SYMTAC Consulting LLC
https://sym-tac.com