I thought that I will oil my Walther action the other day, to make it nice and smooth (rifle actions need to be lubricated). I knew that I need to stay clear of the pressure pot, and regulator, so I just oiled the striker, trigger mechanism and all the moving parts in the action that I could see.
No problem, it felt smooth, but after about 20 shots, the POI dropped so much that I continually missed the kill zone on 50m, and even at 30m.
I took out my chrony, and discovered that my velocity has dropped by 60ft/sec. It was allso not very constant, with big variations. Up to 50 ft/sec inbetween shots.
The only explanation that I have is that the oil made the striker and plunger open and close quicker due to less friction, letting in less air, thus the drop in velocity.
After open heart surgery, and getting rid of all the oil, it is back to its former good manners with good concistancy between shots.
So to all your aspiring young gunsmiths out there, BEWARE dont oil your PCP's actions