Hi All
Will speed loaders for a S&W Model 10 in 38spl work for a Model 66 using 38spl?
Both are K frame so yes
+1. The key to matching speed loaders is frame size. One that will work with a S&W K-frame will work with all S&W K-frames.
And for some Dan Wessons, Taurus, Charter Arms and Rossi revolvers. They all use the HKS 10-A speed loaders
But the Rugers Six series of revolvers and Colt Trooper & King Cobra use a different one (MK-3A) since they have a different chamber profile compared to the K frame S&W's.



























