Measuring cylinder gap / End shake?

[Ron3]

Am I doing this right?

I measured cylinder gap with feeler gauges on my Ruger LCR .357 and new Ruger GP100 .44. Guns were unloaded and not cocked. I pushed the cylinders firmly forward towards the forcing cone (not a lot of force, just "firmly") and recorded the largest feeler gauge that would fit. Then I pulled (again, just "firmly") the cylinders away from the forcing cone and again recorded the largest feeler gauge that would fit.

Finally, I did the math (better check my numbers, not great at math!) and the difference between the two numbers is what I think is called "end shake".

For the LCR .357 with cylinder pushed forward the gap was .0015 inches. Cylinder pulled back the gap was .008 inches. End shake is thus .0065 inches.

For the new GP100 .44 the first measurement was .0025 inches, the second .0035 inches. End shake is thus .001 inches.

One more thing, while the LCR forcing cone is smooth, the GP100 forcing cone looks quite rough. Not the inside, just the flat surface on the outside where the "gap" is. Should I give run a fine stone over it? A little polish, perhaps? Edited to correct: Comparing the forcing cone to others via internet, it's actually not very rough, just somewhat rough.