I bought a 625-6 recently that had an interesting problem. Three consecutive cylinder holes had 1½-2 pounds heavier trigger pull than the other three. After noodling on the problem for awhile, I thought that the ejector rod might be bent. Being the cheap.. err... frugal Scotsman that I am, I decided against buying the $150+ Brownells tool and decided to construct my own.
Well, with a piece of steel U-channel, a couple of right-angle brackets, a couple of bolts, and a dial gauge that I already had, I came up with this -
It looks a little funky, but it works fine. You remove the rear bracket, insert the cylinder assemby into the 1/4" hole in the front bracket, and reassemble the rear bracket with the center pin in the 1/8" hole. You then adjust the magnetic base to put the dial indicator on the end of the ejector rod. Rotate the cylinder to find the high spot, and then tap the ejector rod with a plastic hammer, and gradually get the rod back to true. There's about $12 and two hours in the tool.
Oh, and my 625... it had 0.025" TIR, and after adjustment, I got that down to 0.003" TIR. I no longer have a trigger pull variation problem.
Buck