You can do some online research on castor oil if you wish. I sure did and what I've learned is its difficult to get the straight scoop or atleast a consistent one. But one thing that became clear the AA Baker's standard is not a highly refined grade. Its also known as Pale Pressed and even that has variables depending upon the source. The main thing to avoid is a high moisture content and most grades don't have much anyway.

Apparently modern refining processes include additives to minimize or enhance the acidity. Some of these may improve it from a laboratory standpoint but can diminish the oil's lubricating properties. So far, I cannot tell any difference in the (Sig Baker) AA and the Pale Pressed grade that I've found. From what I can gather the oil found at the pharmacy will work but its unnecessarily expensive to get it there.

I'm using Wildcat Premium 15% Nitro 16% Oil (80/20) with 6 oz of Castor added to the new gallon. (This fills it right up to the base of the neck on the bottle.) The result is around a 14.6% Nitro 20% oil blend with a good portion of that oil being castor. This meets with the recommended brake-in fuel for my Magnum XL 91 RFS engine. And the thing runs fantastic.

Now, after I get 10 gallons thru it I may just buy the 18% oil fuel when I can find it but to be honest, I kind of like the blend I'm using just fine. And its readily available at my LHS whereas the 18% oil content fuel is less consistently available.

I will say the castor is messy but its that "mess" that lets me know my engines getting good lubrication too.

Regards,

Clay