If the answer is obvious please forgive me but, when viewing the cylinder chambers from the loading end, are the cylinders suppose to be completely smooth? When looking through mine they are not. From the muzzle in, about 1/4" back it looks like a ring. Is this a carbon ring or what. I need the education. Thanks in advance. Re: Model 66-1

Normal. Thats the throat. It helps align the bullet with the barrel as it starts its journey. It also keeps someone from putting a 357 in a 38 cyclinder

Not just the 66 or the .38/.357 caliber.
Most modern revolvers have that step-down "ring".
Some older guns, like early Colt Model 1917s, can have a straight-through bored chamber.
Denis

You are good to go. If you are shooting .38s in a .357, or .44 special in a .44 magnum, you could end up with a carbon ring behind the throat. That is an issue, but can be removed through diligent cleaning.

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Even older, even crankier....

Sounds like a carbon build up from shooting 38 special ammo in your Model 66-1. This will not hurt anything if you are only going to shoot 38 special ammo, but if allowed to build up it can prevent .357 magnum ammo from properly seating in the charge holes.

It would be best if you took the time to really remove it from the charge holes.

Thanks guys, I'm thinking some carbon build up since it looks more like a 'band' of carbon. The ridge of the throat would be a small transition (right) and this looks like its about 1/8 inch wide. Sounds like I got some soaking and brushing to do.