A friend recently had a raft of trouble chambering 38 Special reloads in his old M10 S&W revolver.

After eliminating all other potential issues, we discovered the spec COL coupled with the fatter 158 RNL he wanted to use, were just a few 1000ths 'too long' despite being as printed in the manual. The ogive of the RNL didn't quite have clearance on a couple of his cylinders. Changed the boolit shape, they worked fine.

These rounds chambered & shot well in all our other 38 specials.
To test further, we loaded up a few in 158 SWC in otherwise same conditions. They fit fine.

Easy fix in that case. Good luck.

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