You've got your Sparrow right? You can check my work by taking a caliper to yours. You can see exactly where the Sparrow is going to contact the shoulder of any barrel.
I was surprised that I only had 0.015" to spare but my gunsmith tells me CZ does excellent work threading their own barrels in the factory. Took them both to the range yesterday and the barrel to suppressor contact is good enough to put suppressed rounds in the same place as the unsuppressed rounds at 50 yards with similar accuracy. (It was a windy day.)
The key for you regardless of barrel width is going to be the skill of the gunsmith doing your work. That shoulder has got to be cut SQUARE by damn. Or you'll have trouble.
See also the booklet that came with your Sparrow. It says what the distance should be between shoulder and end of threads.
Guess mine is an American. The barrel is 16.5" in length and with the 5" can on the end it is an elegant little piece of work.
