I know just enough about them to look really smart if someone knows nothing and really stupid to a knowledgeable person . I will provide what I have and we'll go from there .
The arm in question is an April 1918 built 1917 , so it's just a tick over 105 yr old . It's stamped not English made and has had the barrel cropped to 3.5" .
It's had a 45 ACP reamer poked in it to make 45 S&W headspace on the mouth with .453 throats and a .451 groove .
All 6 holes aligned correctly with the bore as far as good light in 3 axis' will show to the human eye .
End shake / play is tight giving.004 on both ends with moon clips and AR cases with a trade of about .001 to about.003+ at .004 HS .
Enter the issue it appears that the crane is square . It runs 3 chambers like greased glass , 2 are tight in rotation but not overly difficult to fully engage the lock bolt . Of course one rotates out of the tightness and is readily drawn out DA or SA it takes probably 25# vs the 8ish of the other 3 chambers the last chamber requires manual turning . In the 3 chambers that cause the greif the cylinder won't lock closed and hold enough on the 2 hard chambers to prevent cocking.
My belief is that the cylinder is making either a canted or elliptical rotation but I can't see it or really even measure it. It's like a high primer or sizing induced proud case but since it does it empty that's not it .
Because it's not consistent or gapped I don't think it is the crane . It would drag or be difficult all the way around .
As a lone cause the extractor is out as it is flush and square to the cylinder face , without any suggestion of abnormal wear or poor fitting . It's not dirt I've practiced "when in doubt wash it out" cycled immersed in solvent and fully opened .
As I write I wonder if it has a bulge somewhere that isn't worn enough to shine . ........
Where should I look next ? This isn't a new thing , at it's purchase it was cheap enough to assume it was dirt or end play it's been 6 years and I haven't figured it out and don't have an exhaustive S&W book .