Measuring cylinder gap / End shake?

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.

Barrel face to cylinder face gap (commonly "b-c gap") is measured holding the cylinder rearward (toward the hammer) and measuring the gap between the barrel and cylinder faces with a feeler gauge. The gauge must snugly but comfortably pass through; if it catches or needs force, step down a gauge. Do this from left and right sides as barrel faces and/cylinder faces can be uneven; measure, too, on each charge hole.

Endshake (also called "end play") is the difference between measurements of b-c gap with the cylinder held rearward and forward.

From your numbers, your LCR has a b-c gap of .008", which is perfectly serviceable; it's endshake, however, at .0065 is getting up there and you should consider correction.

Your GP100's b-c gap is on the low side but fine, and endshake is about perfect.

What you're calling the GP's forcing cone actually sounds like the barrel face, and sometimes they're a little rough, but that shouldn't affect performance. The forcing cone is the interior circumferential edge entering the bore, which does need to be properly angled and relatively smooth. If the GP's shooting well, I wouldn't worry.

Thanks!

Your right. I was referring to the barrel face looking a little rough. The forcing cone looks fine.

The GP100 shoots fine.

As for the LCR, it's a few years old, and Ruger advised I'd have to pay to ship it. They did offer to send a shipping label for $30. Fair enough.

But I've heard of people sending guns (including Rugers) for mild problems and new (sometimes bigger) problems being created by the repair. Or a failed repair. This happened to me once. (Taurus)

So because the gun has only had one issue, (cylinder popped open while firing Federal 180 gr sjhp) I didn't want to risk it. I don't plan on firing any more full-power magnum (factory) loads anyway because my hands don't want me to.

It seems the gun is in good working order. It's just a bit worn. Maybe once my wife wears hers down a bit we'll sell them both and reevaluate her carry choice. (I rarely carry mine anyway) If she wants another revolver maybe she'll go for a Charter Arms .44 so we can drop a caliber. (.38/.357)

But I'd rather she go for the Kel-tec P32 I have. It's been a good gun despite its ugly plastic. I think it would be more comfortable for her to carry and shoot. She really shoots the LCR well though and likes it. That counts.

Boy did i wander...