
Yes, 20 yards is pushing the limit of accuracy with a Single Six when loaded with Colibri. This 22 ammo is designed for super quiet shooting when loaded in a 22 handgun and nothing else. As I've posted in the past, if you shoot Colibri in your pet rimfire revolver and expect your revolver to shoot at its best, you will be very disappointed. I don't recommend shooting your pet revolver much past 10 yards when using Colibri.
20 yards is also pretty extreme for a replica CO2 pistol or revolver. Again, 10 yards or so is where these air guns are really at their most useful.
I picked 20 yards, though, for this shoot off to increase the odds of getting a clear cut winner and it did just that. I wouldn't rate either rig to be impressive at 20 yards, but at least there was an obvious winner.
And the winner was ... the CO2 DW revolver.

This was a bitter/sweet result for me. Bitter because I had hoped the Colinri would be accurate enough for serious practice when shooting one of my good 22 revolvers in the back yard (and the Single Six when loaded with good ammo is quite accurate). Unfortunately, using the Colibri in the Single Six at 20 yards was a lesson in frustration. I had as many weird, unexpected fliers landing outside the bull as I had shots landing inside the bull. Based on my recent experience with the Colibri, all I can use it for is ammo for testing function and not much else.
The sweet part was the CO2 revolver. The DW replica is obviously no match grade target gun, but even with its mushy trigger, it was worthwhile to shoot at 20 yards. As long as I did my part, I stood a reasonable chance of keep shots in the 3" bull. Next time, though, I'll step up to 15 yards or maybe 10 yards. It will also make a good indoor shooter, come winter.