What he said!
Some guns have a gap of only .002, but most have slightly larger just in case. Most fall in the range Jack mentioned. .01 or above is a little too much .
Try to slip a peace of 20 lb paper between the front cylinder & the barrel, If that works, try 2 sheets. Each sheet should be about .003.
Also, put in an empty cartridge in the cylinder and have the hammer down to test. If there is any "cylinder shake" that can make a slight difference.