I use #1 buckshot in my Remington 870 (more pellets per shell). I have tried both 3" and 2 3/4" shells and found that with a full choke and a 2 3/4" shell of #1 buck, it produces a great pattern. But then, this is from my 870 12GA.

Here's a list of Buckshot for comparision:
3" 000 Buck ----- 36 caliber --- imagine a 9mm handgun with all10 rounds hitting at once.
3" 00 Buck ------ 33 caliber --- 15 rounds hitting at once.
2 3/4" 00 Buck -- 33 caliber --- 9 rounds hitting at once.
2 3/4" #1 Buck -- 30 caliber --- imagine a very slow .30-30, .308, .30-06 with all 16 rounds hitting at once.