Take a rod the will just barely fit down the bore. It does not have to be long. I use a pin gauge from a set precision ground pieces of hardened steel that step up by .001. I slide the largest one that will fit in the muzzle down the bore. The first thing this tells me is if the bore is uniform. Some guns will exhibit a tight spot and the gauge will hang at that spot. If there is no tight spot and I point the muzzle up and put a finger on the side of the cylinder to create some additional drag and ever so slowy pull the trigger the gauge will drop down into the cylinder before the hammer falls. I worry that the harden pin will damage the firing pin tip so I stick pieces of a foam ear plug in each chamber. While it is important that the cylinder stop drops in the cylinders notch prior to hammer fall (carry up) having the bore in line when that occurs is of even more importance. But, even a pin gauge the is bore dia will drop in cylinder with some error as the throat and groove diameter are larger than the land diameter. But that will be handled by the forcing cone in any event as the beginning of the forcing cone is just over groove dia, . On short barrel big bores in good light you can look down the bore for even light and actually see this to some degree.
Look at the forcing cone, is it centered, smooth and even as the lands begin to show in the bore?
If a revolver has late carry up the cylinder stop will drop and lock up the cylinder and the hand will bind as it tries to continue rotating the cylinder. If it is close the trigger will stack (require more pressure) as it forces its way past the ratchet. You can feel this happen when you are adjusting an ratchet for an over sized hand or installing a new cylinder thats ratchet teeth are a bit big. A over size tooth will stop the trigger, then as you file the ratchet for that chamber the trigger will first go by but you can feel it stack as the hand forces by when you are getting close. I have found this with a couple chambers with on brand new revolvers and usually it will work itself out by dry firing. You can verify that this is the reason the trigger stacks by dry firing with the cylinder out. You will have to press the thump piece back in order to pull trigger with cylinder out.
Another thing to look at is barrel to cylinder gap and end shake. Press cylinder forward with finger pressure and using feeler gauges find the gap, then press it back and repeat the measurement. The variation is endshake. How much clearance there from end of yoke tube to center of cylinder bore when center of ratchet is riding on center of recoil shied. This should be under .002 and to me .001 is ideal. B/C gap should be from .004 to .010. Smaller is better to a point, below .004 any fouling may cause drag. A wider gap will allow more gas to escape, but velocity by the inch tested a revolver, first having the barrel tight to the cylinder 0 clearance and fired it, then set it to .001, then .006. The amount of velocity lost was always far greater over the first .001 of gap than the next .005. With 158 gr 357 Federal HP in a 6" barrel they lost .55 fps a .001 gap and just `14fps going from .001 to .006. So while I like to shoot for .004 to .006 I am not as concerned as I once was by .010. as I seriously doubt the velocity loss by that addition.004 amounts to much. I do not carry a feeler gauge with me when I go visiting gun and pawn shops. First I have the tools and ability to fix it. Next you can develop a pretty good "eye" for the gap by looking at enough revolvers. You need to get the gun square to your eye to see the gap.
I also know this. Take something like a 357 or 44 with a normal gap and fire it with construction paper or artist paper say 4 " from it. It will blow holes in it, do that at 12" and you won't get holes, but some powder marks, at 18" it is pretty tiny. I imagine with a higher pressure round like the 460, 5500 or 350 Legend running at 60,000 psi instead of 36,000 the amounts will increase, but quickly drop off as the distance increases.
Here is an interesting observation. Holding a hand gun normally you should not feel any powder peppering on your face. But, if you put that revolver in something like a Ransom rest and move your face closer you will. I figured this out when making a revolver into a carbine, which when used puts you face closer to the frame. It also buts your elbow well down and below the barrel cylinder gap. While the gun is perfectly in time you will feel very light peppering on your face, but Not your elbow.