I've written a response to this question three times now; each time being completely distracted and deleting the post prior to posting.
Shimming the axle will provide a solution to your problem.
It might also be worth noting here other ways which you can use to solve the same problem.
- A bodge - Remove the hammer and turn it upside down and punch with a rounded punch around the four sides of the axle hole. You needn't punch very hard just enough to move a small amount of metal around to close up the fit. This will provide a solution to the problem, I call it a bodge, only because people are not mad keen on peening parts on guns. On a low value gun its completely acceptable, and is completely hidden once the hammer is back on the axle. Quite often cheap old guns have evidence of this being done in the past. As a repair it works though is not the only option.
Another option is to fill the hammer axle hole with weld, re drill the hole then punch it out to square with a tapered square punch ( you'll have to make this ) this is a great method though getting the orientation of the hammer to the axle can be fiddly.
I have in the past welded up the axle, only because the axle was appreciably worn some how; its fiddly and far too easy to burn through into the threaded hole which the shank of the hammer retaining screw goes into - can be done; not recommended.
