Agree with the above. 30W motor oil is commonly used as a cheap substitute for Mobil Vactra 2 Way Oil by people with old machinery they want to maintain on the cheap. Vactra 2 is better if you have a machine shop around that will give you a little.
3-in-1 Electric Motor oil is 20W, so it's a little thin for best wear prevention and precision. What you are looking for is not only lubrication and wear prevention, but an oil with enough viscosity to keep a thick enough lubricating film to float the ram in its journal and tend to self-center in it. That way it isn't rubbing or wearing much of anywhere, and I'm sure that's the basis for the choice of viscosity. Thicker oil would float it, but one that's too viscous will cause drag and may tend to suck air in the end that is entering the journal and not flow fast enough to back fill these cavities as they form. The choice is a best compromise in the end.
Detergent motor oils are great for a system that has an oil pump and a filter, because the detergent, even better than using a thin oil, cleans and suspends dirt and grit and other deposits for the filter to remove. If you don't have oil circulation and a filter, though, the dirt and grit are sleeping dogs often better left where they lay. The lack of a filter is, AFAIK, the main reason detergent oils were not recommended for small engines for so long, but newer ones are designed to put up with it. That's probably both for convenience and possibly because they figured out having motors ultimately wear out and need replacement was good for business.
I doubt the multiple viscosity additives matter much one way or the other to a machine like a loading press that doesn't get hot, just as long as the room temperature viscosity equals the 30W more or less. I've never inquired as to which range you would buy to achieve that equivalency. I can tell you that Mobil 1 0-W-20 synthetic detergent motor oil makes a very good gun carbon remover if you aren't in too much of a hurry for it to act or if you use it when the gun is hot. I was told the AMU uses it for all their general cleaning and lubrication in their match rifles.
) and picked up my quart of 30W non-detergent. Lubed up the rams on my new Dillon and my old RCBS single-stage. 30W is definitely thicker than Browning gun oil.