The limit is about .004".
To measure you can use automotive feeler gages.
A simple method is to measure at the barrel/cylinder gap.
Press the cylinder forward and hold it while you gage the gap.
Press the cylinder to the rear and gage again.
The difference is the total end shake.
Or you could use the cheap guy's feeler gauge. Pull out one of your hairs and use that, human hair is usually .003". Even though I'm bald I still remember that. Or pull out your wife's hair, and then run fast !!!