I recently ran out of Hops #9 oil. Instead of going to the store and spending $6 on a small 1 oz bottle, I decided to use some left over fully synthetic Castrol 5w-30 engine oil. A few weeks later, I went to the range and put 250 rounds through my SR22. When I got home and field stripped my gun, I realized that the outside of the barrel and the slide rails were still wet with oil. This oil seems to lubricate better, and at 1/10th the cost.