Snake gun load help, accidently suffering from success

Hello all, so I own a Pietta 1851 .44 cal revolver that I carry around the homestead because we get the occasional rattlesnake around the house and don't want them messing with the chickens. Recently to improve the patterning of the birdshot loads I use for this purpose, I purchased a CSA JH Dance barrel for my 1851 made it smooth bore, and did the required modification to make it fit on an otherwise incompatible sub model for that barrel. Well now I'm on the other end of the spectrum, I can't get enough spread to not have to worry about causing too property damage.

I use the landmark distance of 6ft for all my testing because realistically, that's as close as I would ever get to a living rattlesnake, with the old rifled barrel I was producing a 6in pattern at that distance, after tinkering, the best group I could get with a slightly different loading method out of the smooth bore is about a 2in pattern, a very tight pattern that I worry may blow through the siding of stuff like the chicken coop or take a chunk out of the house foundation.

The current best load for the smooth bore in order of loading into the cylinder: 35gr FFFG Blackpowder > Wad > Compress Powder > 80gr of #8 Soft Lead Birdshot > Wad > Compress > Bore Butter

I'm wondering, what are my options for inducing a little more spread? When I undertook the whole project I expected some gains, but I got far tighter patterns than I ever imagined I would with the new barrel. Can anyone weigh in on this or maybe offer some loading advice?

I read an old reloading manual where they talked about Spreader Loads. They said layering the shot with multiple over powder wads. So drop the powder, a thin wad, 1/3 the shot, then continue until full.
Also try adjusting the powder charge and shot size. I know most my shotguns perform different with different shot sizes.

More powder less lead spreads faster from what little I understand. Not sure how much difference you’d see at 2 yds though. Maybe try less pellets which will increase that speed and maybe spread them out faster.

You might try slightly flattening your shot prior to loading. Flattened shot will not fly as true as round shot so the pattern should open up a bit more.

As another (possibly last-ditch) effort, consider boring out the barrel as far as you safely can. That should allow the shot to spread out just a bit more prior to exiting the muzzle, and thereby possibly allow a greater spread on target. It is doubtful there will be any problems with pressure affecting the thinner-walled barrel with the small powder charges you are limited to.