The window on a model 10 should be the same as all K frames, I can adjust the barrel to fit the cylinder. .06 shorter cylinder shouldn't be a problem except maybe on longer bullets. If I stay below 52 grains the 1 in 15 twist should be OK. That is what Jet barrels run for a twist also. I had a 222 Remington with a 1 in 14 and it did fine with most 55 grain bullets and loved the lighter ones. If I have problems I can drill out the barrel and line it to 1 in 12. I have several thousand 40gr 2224 bullets already from when I had my 222.