I shoot J bullets from 123 to 187 gr. out of my Chinese and Yugo SKS. I get the best accuracy with .310 to .311 dia. J bullets and .313 dia. 167 gr. gas checked cast lead bullets.
For lead plinker and small game loads I like 12.5 grs. of Alliant 2400 MV is around 1400 fps. and dumps the brass right at my feet,If I want to push the cast lead bullet a bit faster I use 14.5 grs. of 2400 MV is just over 1900 fps. and tosses the brass like Russian steel case. For the 187 gr. FMJ surplus bullets I like 18.0 grs. of Reloader #7 I mainly use those for blasting ammo they hit hard and penetrate well at close range.
Now to the J bullets,for 150 gr. bullets like Sierra .311 Pro Hunter SP,Prvi Partizan .311 BTSP,Speer .311 HotCor SP I like 24.0 grs. of Reloader #7 the MAX load is 24.8 grs. in the Lee reloading manual,it pretty much duplicates the Wolf 154 gr. SP but is much more accurate,five shot groups generally run under an 1" or less at 50 yds.
At 400 yds. the 7.62 x 39 starts to loose a lot of steam,bullet drop almost doubles regardless of bullet weight used between 300 and 400 yds. With a 100 yd. zero both bullet weights drop around 25 to 30" at 300 yds. but at 400 yds. the 123 gr. drop about 55" and the 150 gr. drop about 66" and at 500 yds. the bullet drop doubles again into the 120" range.
You also need to take into account that out past 200 yds. which is a stretch to get reliable expansion using the steel jacket 150 gr. bullets expansion is going to be non existent,even using a good commercial 150 gr. .310 to .311 dia. bullets which you will have to hand loads will be questionable at 200 yds. as far as expansion is concerned.
For 150 gr. hand loads I like to keep any shot on big game under 100 yds. The 150's and up make great thick cover bush buster or steel target target thumper's. The .310.5 187's Bulgarian surplus bullet I shoot at time do drop considerably but they group well,you just have to find the rear sight elevation setting that works best for the range your shooting at. I've tried a few different .308 dia. bullets but the group like crap and due to the undersized bullet you tend to loose a little more gas blow by which causes some MV loss.