Bought a StormLake 5.2" barrel for my 31G4. Chronografed 2 loads today thru this barrel and the original 4.5"er. CED chrono, 1st screen at 10', about 80dF, all samples 10 rounds. Cartridge OAL 1.135" to 1.140". PD load--125g. Barnes all-copper TAC-XPs-- 4.5", 1359FPS, SD 12.5 5.2", 1365FPS, SD 9.0 ... < corrected This load uses 9.2g. [each load weighed] HS-6, the overall-best powder I found with this long bullet, WSPs, and Speer nickel cases. Practice load using new (to me, at least) Montana Gold 125g. HPs-- 4.5" barrel, 1364FPS, SD 7.0 5.2" barrel, 1373FPS, SD 17.9 This load uses 8.5g. 800X, WSP, Speer nickel cases. 800X is a course, large-flake powder which does NOT dispense evenly from the mechanical powder measure I use for my practice rounds. I'm surprised at the small differences; I expected something more like 20 - 30FPS. The SL barrel is nicely machined and fits a little tighter in the slide. I think the chamber is slightly smaller than that in the original Glock barrel; my former PD load won't chamber in it.