I would first see if it was still good by smell, color and visual.

Then e-mail the company to see if they would have any data for you.

It actually works well as a 45 and 38 target powder but was discontinued around 1966 or 1967 I think. I never used it but one of the gentlemen that started me in reloading had old data on this
powder........ but I would try to verify this data before using it, since it is second hand to me.

P-5066

38 spl
148 wc 2.9grs at 744
158 LRN 3.8 grs at 875 max load.

45 ACP
185 Jswc 4.2 at 655
185 Jswc 5.8 at 1005 max load
230 fmj 5.7 at 833 max load