If you're really worried about it, slip a feeler gauge in the gap to measure it, should be around .006" or so.

If there is no drag between contact of the two surfaces, and if functions for a complete revolution, shoot the thing and check the barrel stub area for any bullet shaving or lead deposits. If nothing shows up, all is O.K.

Bob Wright

One other thing, check for cylinder end-play, make sure recoil won't slam the cylinder up against the barrel stub.

Bob Wright

Thanks Bob, the end play seems real good and tight. I will take the gun out and put a few rounds through her and see what happens. I will post results.
Jim

Not hijacking the thread. Have Model 66 bought new and used on the job in the 1970's. Has 4" pinned barrel .
Found a 6" barrel yesterday and want to swap barrels out.
Have never driven a pin out and unscrewed a barrel but have all the tools.
Because the new barrel has a groove in the thread for the pin is there any need or way to adjust the barrel for headspacing (assuming the same spacing as above)?
Would seem aligning the groove would position the barrel with the correct headspacing.
Just found this site and would like to introduce myself. After moving on from law enforcement I have been tempted to enroll in a local gunsmithing school (Colo School of Trades) but it would take $21,000. Thanks, Thor

Thought I would check for any suggestions. Even after logging in the page shows me "offline"--strange. Got to wondering if that pin might be tapered requiring it to be drifted out one way only. Anybody know? I'll just cruise around the site for awhile. Heard of HR 45 yesterday--what it that all about? ThorOdinson

I'm still wondering if anybody knows about barrel exchange. Handy to have the cylinder clearance. Might just give it a shot and tell you how it went. I suppose I can measure the existing gap before I start and match the new one to that measurement.

With no responses I decided to wing it. Here is what I did.
I measured cylinder gap from factory with feeler gauge set (automotive, flat, not wire guage for plugs) About .005-.006.
Opened cylinder and removed screw in sideplate that retains it.
(Have the little screwdriver that came wih the revolver--it fits perfectly and does not bugger up the screw slot)
Slide out cylinder and pivot assembly.
Use several layers of innertube to pad vise and clamp gun.
Use Craftsman 1/16" punch to drift out pin holding old barrel--pin was not tapered so can drift out from either side.
ReClamp just barrel in padded vise
Use chunk of wood (I had a 1X oak bed slat) and insert into vacant cylinder opening. Wood about 15" long.
Remember righty tighty and lefty loosy. Use slat to unscrew frame from barrel--may take a rap from soft mallet to "break" the set on the threaded barrel.
Screw in new barrel until it seats and grooves on top of frame and barrel align.
New barrel did not have spring loaded catch so I had to drift the pin holding the old one. Takes 1/32" which is pretty small and my set doesn't go that small. Carefully ground down hardened nail (for concrete) on bench grinder. Worked perfectly.
Install spring and latch in new barrel and using larger diameter punch (I had a brass drift about 3/16").
Cleaned and relubed cylinder pivot pin with LubriPlate. (No WD40--too light a lube and evaporates. FYI WD = Water Displacement
Replaced cylinder and reset screw.
Cylinder gap too tight. I found it easiest to draw file the forcing cone of the barrel then campher sharp edges on bore's forcing cone (the hole) and lightly radius the exterior edge.
Cylinder closes and latches. Indexes whan hammer cocked. Checked cylinder gap with guage when closed. Looks good.
If I had a lathe or mill I could have used those and then radiused edges.
Looked through pin hole in barrel--back lit. Aligned perfectly so I drifted the 1/16" pin back in the frame.
Swabbed barrel and cylinder with Hoppes and patches to remove any filings or debris.
Haven't shot it yet but will probably try some SWC .38's that I cast from virgin lead, then go to .357.
Anybody think I forgot anything---post a message. Thor

I've not done a lot of wheel gun work but I did talk to a buddy of mine about what you have done and it appears you have done well. let us know how it shoots