A couple years ago, I actually read the manual for my Dillon press They suggested using 30 weight motor oil. When I asked them if I should use detergent or non-detergent oil, they said it didn’t matter. I had a quart of 30W non-detergent motor oil on the shelf so I used that on my press ram. Several weeks and thousands of rounds later, the oil film was still visible on the ram. I was quite amazed because I had been using a liquid spray oil up until that point and it disappeared after a few hours of use.
I decided to used the same 30W ND oil on my pistols and low and behold, the same oil film remained after shooting several range sessions and matches. I’m still using it and see no reason to use that outrageously high priced “gun” oils any more.