Russianblood, I use 4f in all my .31 pistols with good result. The 4f is not quite as accurate as 3f but I am going to 4f Swiss and see if I can get more speed and accuracy out of my .31's. They have had a steady diet of 4f for a long time now and I cannot see any problem. I shoot as much as 200 times a month. Mind the wedge tension and you will not have a problem.