Does anyone know what powder IVI used in 1979 in their 7.62 ball C21A1, bullets are 147.5 gr FMJ and the powder avg is 42.7 gr.
There are 2 types of powder out there, exact "Labeled" burn rates (IE. BLC2, IMR 3031, H380, Reloader 22, ect). Then there is the other kind which is neither here nor there, and this is the stuff that is sold to Ammunition companies, military, ect. They are told, "well, the powder is somewhere between H335 and H4895 (Or IMR 3031-IMR 4895, ect.)" Powder company then suggests what the equivalent load data should be.
There are 2 ways you can go about replicating the '79 IVI ball load. Load for pressures and velocity that come close if not match the IVI load, or to make it more difficult, go through tons of powder/load data, find a powder that given a charge of 42.7 (42-43) that will "theoretically" yield the approximate 2750fps (give or take 50fps) and ALSO matches same ball park of the given pressures.
KEEP IN MIND (BIG PLEASE HERE)
If this load is for 308 Garand, M14/M1A, AR-10, or other suck militaary type semi-auto rifles (probably throw in sporting semis too), they are ONLY designed to handle medium burn rate powders. ONLY! To slow or to fast can cause the gun to be damaged or much worse. I have seen a Chinese M-14 that a guy ran his buddy's reloads through, and as it turned out, the reloads were in fact for a bold gun, over pressured for an M-14 and he was running a slow burn rate powder.
http://www.reloadbench.com/burn.html Here is a burn rate chart, and the military Semi(Full) autos should be kept with in #94 (IMR 3031)-#120(IMR 4064). Trying to reproduce the ball load, your best bet is to check these powders to begin with.