Misfeeding.

[Chaffin]

If you can find them, I swear by G&G Mid caps. They work fantastically. They are full metal and they make a few different kinds.

They have the 40rd ones, the 70rd ones, and if you buy the G&P full metal ones, there are 120rd ones.

If you look around they can be had for normally about $10-13 a piece.

[Arch-Angel(3.14)]

Just listen to Shamrock and spend the extra money for superb mags. I use real P-mags and haven't looked back since. As for the oil, as long as it doesn't have petroleum distillates or other rubber-harming chemicals, it's safe to use. If you choose to oil your hop-up; however, keep in mind it won't function properly for some time due to loss of friction on the bucking. Personally, I have found that by taking a gun cleaning patch and putting a drop or two of oil on the patch then running it through your barrel with a cleaning rod works best.