I am having a problem with a S&W 651 convertable revolver. I have tried everything I can think of with no luck. I am hoping that one of you wizards out there can come up with a better idea.The gun functions fine with the 22 LR cylinder but locks up with the 22 Mag cylinder. It will just completely lock up. The hammer won't move, the cylinder won't move and it is very difficult to open. The ejector star and rod are clean; the ejector rod and the extractor rods are straight. The ends of the cylinder are parallel within .0005. The extractor star is not distorted and all the parts in the assembly move freely. The two pins go in and out of the star with no problem. The same crane and screw are used on both cylinders. I'm baffled. what haven't I done?

Do you mean that it locks up after you fire a cylinderful of ammo, or does this happen when you install the magnum cylinder?

It locks up when I load and try to fire. Locks up usualy after the second round. Makes no difference if I use CCI, WW or Hornady ammo. No drag marks on recoil shield or on the brass. ?????

There has to be a "drag" on either the front of the cylinder, or the rear. If there is at least .001 clearance at the front end, then it does not have correct headspace at the rear. Measure the headspace on the .22lr & see if the magnum cylinder is the same?? Does it spin freely without ammo? Are the magnum shells fully seated? Good Luck. Judge

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Martin Co,FLA(finally made it)

I'm not sure what headspace is on a revolver. I understand headspace on rifles and semiauto pistols but I've never encountered it on a revolver. Please be good enough to tell me what to measure and where to measure it. Yes, the cartridges are fully seated. The rims are recessed into the cylinder on this gun and those recesses can't get any cleaner. That was where I started my search and things have downhill from there. Many thanks to all who help.