Ok, I checked my 5 1/2" Single Six and a round will go all the way in from the front. Which is not a surprise as if you look through the chamber there is no step or throat in the chamber.
Something to consider here is that the .22 LR uses a heel based bullet where the bullet diameter and case diameter are virtually the same (a .226" chamber diameter for a .224" case diameter and a .224" bullet diameter), unlike straight wall centerfire rounds, or even the .22 WMR where the case diameter is larger than the bore and bullet diameter (.242 versus .224).
In my Single Six the .22 WMR cylinder has the expected step.
In terms of accuracy, I've noted it is a tack driver in .22 WMR, easily shooting 1" 6 shot groups at 25 yards. With .22 LR the groups depend a lot on the ammunition. WIth standard velocity ammo, the accuracy is not as good as it is with high velocity ammo, and I attribute that to the larger .22 WMR bore dimensions and the need for the .22LR bullet to have more pressure to properly obturate into the bore. With high velocity ammo, the accuracy is good - on the order of 1.5" at 25 yards.
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Here is where I think the straight through .226" cylinder in the Single Six makes a great deal of sense. The bullet has a fair amount of travel before it leaves the cylinder and enters the forcing cone, and it makes sense for the bullet to start obturating in the cylinder to a larger diameter than would be the case in a .22 LR bore. If it used a standard .22 LR dimensioned cylinder, the bullet would first obturate to the diameter needed for a .223 bore, then it would have to obturate further for the .224 bore once it gets to the forcing cone. It makes more sense just to let it bump up all the way to .226" and then enter the forcing cone slightly over size, as you try to do with a cast lead bullet in a centerfire bore. An undersized bullet entering the forcing cone and rifling is a sure fire way to have leading issues, while allowing the bullet to expand in the cylinder will prevent that issue.
I have personally never had leading issues with my Single Six and mine has well over 1000 rounds of .22LR through it. I have not shot significant amounts of SV ammo in it because it isn't all that accurate with SV ammo, and it's possible that the lower pressure rounds, not obturating enough in the cylinder may create the potential for some leading in the forcing cone and initial portion of the barrel as the undersized bullet skids into it.