I don't oil the spring at all, though a little oil does run down there when you stand up the rifle with a wet BCG.
I have never oiled my buffer sping . When I clean my buffer and spring every 500 to 1k rounds it always has some oils on it . I'm sure you've noticed after your gun has been sitting around for a few days or weeks . there is oils coming out between the two receivers by the rear take down pin . It leaks down in to the buffer tube as well .
+1 on using more then just one mag for your test . If you don't have any now , somebody at the range would most likely let you use one . I was having a few problems with feed jam issues . It took me awhile to figure it out but it turned out to be my 20rd Pmags . I have like 7 different makes and or sizes of mags . I have not had one feed jam sense I took the two 20rd Pmags out of the loop .