Mod choles are all over the map. Also, with a mod choke the Honady Buckshot load will pattern the tightest with that weird wad they have.
I used Full and extra full chokes with #4 buckshot, and have loaded my own custom #4, F buck, and BB loads since the mid 80's. Ballistic products is your friend on reloading components.
Of the Modified chokes I used, the Browning BPS was the tightest.
Remingtons, the Full and factory Extra full choke produced 100% patterns at 40 yards in a 20" circle Surprisingly enough, the 00 and 000 Rem factory 3" buck loads shot 100% in 15" circles at 40 yards.
If you are STUCK with a fixed modified choke, consider the Factory Hornady #4 buck load first. In my old fixed Mod choke Remington 870's, Rem, Fed, and Win 3" patterned 70% in a 30" circle at 40 yards, Ithaca 37 fixed choke was even worse. I killed a lot of coyotes with these mod 870's, but multiple shots were used at 40-50 yards. Extra full turkey choke in the Rem, Beretta 390, and 391 is amazing.
Lot of internet experts will repeat what they have read on how buckshot performs best with cylinder and Imp cylinder, but I have patterned many, Hundreds of bushshot patterns in Remingtons, Beretta's.
What is really amazing on shotgun patterns is the point of aim vs the point of impact....gun fit.
