I've posted elsewhere...but will pass along my tip with washers...Bend a steel washer into a bit of a "V" shape then drop in the hole. You can custom fit the height by assembling the gun (with washer in place), & tap the muzzle lightly with a block of word until perfectly adjusted. You can continue to use with the washer in place, or use it's virtual height to establish the thickness needed for a permanent alteration. Many ways to skin the final solution. I have a total of 4-revolvers using a "V" washer (retained by heavy grease) to fit the assembly, & spent no more than 20 minutes total on all 4.
Not perfect, but it works.
Slim