The best 7.62x39 load data I've found is in the Lyman manual. I'm not sure which number manual but it's the same in a few editions of Lyman manuals. Best regular powders are AA1680, RL-7, H4198 and current production IMR-4198 is now the same as current production H4198. If you see different load data for IMR-4198 and H4198, use the hotter of load data for either one. It will usually be a compressed load. The very best powder, though expensive, is VV N-120. The old load data for it was plenty hot and the newer load data is even hotter. I use older load data from VV. Sierra, Speer and Hornady have some data that can be cross referenced with Lyman load to see if it's close to correct but the Lyman load data is right on. Some manuals reference .308" bullets and some reference .311" bullets. Some load manuals have load data separated fo both bullet diameters. Most 7.62x39 dies include expander plugs for both .308" and .311" bullets. The Lee expanders can be a bit large and the larger one can be polished down a bit and the smaller one be used with boat tail .311" bullets without working the brass too much. The RCBS expanders are about 0.001" smaller and Hornady makes some dies too. The larger of he Lee expanders is good for cast bullets but the Lee universal expander for .312"/32 pistol caliber cast bullets is even better for cast bullets.
Load data
Do your best to find CCI#34 mil spec primers. If not try Remington or CCI primers. Winchester and Federal primers aren't the best primers for AK's and SKS's.
Standard bullet weight is 123 grains (to 125gr) in 0.310"-0.311" diameter. FMJ or soft points loaded to 2.19" should work well.
The easiest powder to load is Accurate Arms A-1680. The Accurate Arms max load is 25.5 grains, the Lyman max is 25.7 grains. These loads should be safe. The Speer manual data is a bit hot with this powder.
Reloader #7 work well. It's now made in Sweden and a bit slower than before. Old data max'd at 25.5 grains, Lyman shows a max of 26.8 grains which might be alright but will really fill the case.
H-4198 is easy to use and hard to overcharge. Max load is 26.5 grains but work well with less. I like 26.0 grains.
Current made in Australia IMR-4198 is the exact same powder as H-4198. The load data listed for it is for older made in Canada IMR-4198 which doesn't work as well. If you choose this powder try to get the made in Australia version and use H-4198 load data.
H-4198 and IMR-4198 can be downloaded quite a bit and still give decent results.
I've used a lot of the older RL#7 and it really good. I haven't used much of the newer stuff.
For me A-1680 work alright when loaded near max but downloading has only been so-so for me. Others report good results downloading it a bit though.
These powders have the right burning rate and are easy to find good loads. Slower powders do some really weird things and faster powders often don't make enough gas for the gas system to work the action.