The range that I use has stations from the shooting line for 25/50/75/100 yds in line. At 110 tards, there is a 10 ft tall berm. When I've checked buckshot at 25 or 50, it's not hard to see what's happening at 110.
Given that your thinking of a combat situation, two thoughts come to mind.
IIRC, most buckshot loads are unacceptable at 50 yards and based on observation and memory, covered about a 6 ft X 6ft impact area at 100. The sole exception I tested was a Scattergun Tech 870 with the modified choke tube and WW #1 plated shot - 2 3/4, 16 pellets. I would get 4 to 10 pellets on an E type target at a measured 50 yards. The key is testing throughly. BTW, there was no consistancy to the number of hits (one shot 4 hits, next 10, etc., etc.).
The other thought is based on observation during buckshot only hunts for deer. I have observed the double/triple tap technique used successfully at extended range. Mostly by slob hunters using an auto. I don't like it for game as it's sloppy, but for two legged varmits.....
Other questions you need to answer for yourself are - if the target will be that fleeting, wouldn't disengagement be a better option? How do you practice target ID if the terrain is that thick with vegatation? I have not tested this, but just how effective is a .32 caliber round ball going to be in excess of 50 yards?
Food for thought.
Giz