What choke is the barrel, I always use a full.

I shoot squirrels in south Mississippi too, and shoot a T/C Contender Super 14" 410 loaded with Remington 3" #6 shot. Out to 25 yards, it has killed literally hundreds of squirrels and more than it's share of rabbits. It may be limited on range but it sure is fun to hunt with!

I hunt with # 4 high brass in 20 ga for squirrel. Maybe open up the choke for brush? Heavier shot patterns tighter anyway.

I live in north Arkansas some places are like that brushy along the rivers. I always carry some #4 but mostly 6's. I did get a reloader and ordered some magnum #5 to load to try on them. If that dont shoot that good. I am ordering some nickel platted 5 1/2 shot. I use a mossberg 500 410 TSS Turkey gun. The oak trees are big . The nickel platted mite be better.

"Shot size is a poor substitute for pattern density" & having said that, squirrels are tough little buggers & I don't trust anything smaller than #6 lead. I don't shoot steel anything at anything. If I can't shoot lead, I got to bismuth or tungsten alloy. I am glad to hear some people don't want to hunt squirrel. That leaves more for me! I thoroughly enjoy a few good squirrel hunts every year, even though my time is divided between a number of other types of game. I started with a .410 sxs shooting #6's. I still use 6's but found the .410 lacking for anything over 20 yds. or so. The 20 ga. with 7/8 oz. of shot was a vast improvement. If you are having trouble seeing squirrels in the brush, I bet the range is not too great. 6's don't penetrate brush as well as 4's or 5's but there is a lot more of them to find an opening. I really doubt you will kill more with larger shot. BTW, I don't know what I would want to use it for but I regret selling my .410 anyway. A 28 ga. would have been a much better choice. However, if you enjoy hunting with the .410, as I once did, "Go For It"!