Speer 8 & 9 has data. Norma's website also. I have compared charge weights for similar bullet weights with .308 Win and they are close I'd stay 1 grain under max with .308 data for the 7.7mmx58 loads. RL15, IMR4064, 4320, 4895, N203 and even W844,846 have worked for me.
I am gonna try some Soviet Extra match bullets and Target bullets in 7.7 and 303 Brit.. Hopefully I can find some powder data but I will figure it out. I will have to pull bullets from some amazing loads but these bullets are very impressive in Soviet rifles. I have got to try them in these other rifles.
The good soviet LB bullets are also very effective when loaded in 7.7 Japanese cases. They are also pretty cheap.
I have used all kinds of powder for my 7.7 rounds any imr,hodgen 4895 , varget, imr4064,ram shot big game, all gave excellent results in my 3 rifles. There are many more rifle powders will work but i like those choices for all my bolt actions.from 8mm.06 to 7.6254r. Works well in all ,i suggest the you buy new lee or hornady reloading manual , the cost is well worth it and you have every load you will ever need in those two manuals.sierra loads are good as well , i just prefer hornady over all else , personel choice .