After much research, i decided to relube one of my guns with engine oil. Not just any oil, but fresh Mobil 1 turbo diesel truck 5w40. IMHO, perhaps the best broad application oil around. The gun is a .22lr GSG 5 PK 9" barrel. This gun works pretty good and has about 600 rounds under its belt. Just putting this oil on and wiping it back off does really well in cleaning the gun. I made sure to get the oil everywhere and then wiping excess back off. I'm thinking the extra additives of an HDEO along with the smooth 5w cold performance will provide me some nice results. This gun sometimes will not have enough energy to fully cycle with low velocity rounds. It runs great with high velocity and Rem oil. For science, i will be test firing the gun soon with subsonic ammo as well as high velocity rounds with the 5w40 lube. Any thoughts on how good/bad this should work? I've only ever seen people say things like 15w50, or 0w20, or plain 10w30. Why not an HDEO?