First, let me say that I always clean my lock internals every time I clean my rifle. That is important because there are some lubricants that will gum up over time if you don't regularly clean your lock. So, having said that, I have found that just about any of the modern gun oils do just fine in my locks. I stress oil because I do not like the use of grease in my locks because they tend to collect fouling more than a light bit of oil. I have used and continue to use various modern oils with very good results. Such oils as 3 in 1, Break Free CLP, Frog Lube, Remoil, etc. All have served me quite well. While WD-40 is an excellent water displacing material and I use it extensively as one of the final steps in cleaning my guns, it is not the best thing for lubricating the internals of my locks and I do not recommend it for that use. I also do not recommend the use of most of the historical lubricants such as bear oil, sperm whale oil or its modern equivalent, jojoba oil, etc. not because they do not lubricate but because they do not lubricate as well as the modern oils and they have no anti-corrosion additives and, thus, do not protect as well as the modern lubricants.
In conclusion, let me say that I do not wish to enter into a debate with others concerning my recommendations, it is your rifle and your investment so the final decision of the best lock lubricant is, for better or for worse, yours to make. I can only share with you what my thoughts are on the subject. Good luck in your choice. :hatsoff: