Single Six old/new cylinder length

I recently purchased an old model single six 21-xxxxx. Was supposed to have the mag cylinder, Ruger did confirm it is a convertible, but the dealer can't find the extra cylinder. (If you knew the store you would understand, lets leave it at that.)
They had four extra magnum cylinders lying about so we tried them. Everyone was about 1/8" too long.
My question is this, are new model cylinders longer and that will be the challenge?

1/8th of an inch sounds like a LOT compared to my OM & NM Single-Six revolvers. Are you sure he was checking Ruger cylinders?
The frame size & window size hasn't changed on the SS since it was introduced.

If they were Ruger cylinders they should have 3 numbers scratched on the front of the cylinder. I think contender has it figured out. They probably not Ruger cylinders. To be period correct your magnum cylinder should be fluted and not marked magnum on the cylinder at all.

My sample size is not large (1 to be exact) but I purchased an OM SS in 22 Mag. A friend gave me a NM SS Co Centennial 22 LR cylinder. That cylinder was too long and the gas shield had to be trimmed slightly so it would not bind. Got lucky on the cylinder gap. So, in this case, yes, the NM cylinder was longer.

In my experience the extreme spread in single six cyl over length is no more than .010", even between old and new models cylinders.

An 1/8" difference is impossible.

I may have over estimated the size. I am sure they are Ruger cylinders as I was involved in the test fitting. I do appreciate the input. I think I will have another look. I am hoping the original turns up.
One of the ones I tried was fluted, if that's the most likely I'll certainly try and get a photo.

Take the fluted one and you can stone the gas ring in front to fit the frame.

If someone is looking for cylinders for NM's here is a source. http://www.rugercyl.com/index.htm

I have an OMSS, a NMSS, a NMS10 and a Wrangler. Both SSs have .22 and .22 mag cylinders. All 6 cylinders are interchangeable as far as length goes.