Let's see, Dixie tri-ball at 1100 fps and 315 gr. versus .44 mag 240 gr. at 1300 fps (pistol) give the tri-ball about 846 lbs of energy versus 904 for the .44 mag. Rem .44 Mag Super-X from a rifle gives you about 1760 fps with muzzle energy of a whopping 1650 which is substantially more than a single tri-ball. So each ball actually has a larger diameter and less energy than a .44 mag, but combined the three are impressive.
I put 15 rounds down range out of my 870 with an 18" non-choked barrel. I have a Knoxx-Spec Ops stock that helps with recoil. Recoil was still significant. It is not a cushy load at all. In fact, the three balls produce a combined weight of more than 2 oz. So that is a big load.
The patterning was bizarre and quite variable. At 15 yards, I shot 3 rounds of which two produced groups of 3" or less. The third has 2 balls touching and the third 6" off to the side. At 25 yards, the groups ranged from 3-6", often with 2 balls hitting on top of one another or impacts touching. At 36 yards, the groups opened up to 6-12+ inches, the + being shots that left the target off to the side by some unknown distance.
In short, the pattern isn't anything resembling uniform on a consistent basis. I think this likely has to do with the shot sleeve that holds the shot that sometimes holds onto two of the balls much better than the 3rd ball.
With that said, the patterns were significantly tighter than with standard 00 buck for which I get an average spread of about 1" per yard distance from target. For example, at 25 yards, I get about 22-28" spead.
On the down side, I was shooting a Marine Magnum that can handle the power and size of the rounds in the chamber, but once fired, the shells were actually longer than the ejection port and two did not want to immediately eject and hung up.
The Tri-ball buckshot load takes the ordinary smoothbore into another realm of power and penetration for anything from wild hogs to police roadblocks.
Why are you wanting to penetrate police roadblocks? Most people trying to penetrate police roadblocks are engaged in illegal activities.