I am wondering if, were it safe and possible, jacking up the velocity of this round by 100-150 feet per second might improve accuracy and performance?  I reload, but have so much combloc surplus 7.62 x 39
that I haven't really bothered to reload for it.

Has anyone out there done any experimentation with this round?  Even with a benched SKS it shoots pitiful large groups.  I would like to try to improve the breed if possible.

Accuracy can be improved greatly if your rifle is capable of it, but that varies gun to gun.

Velocity is pretty much maxed out and duplicating factory velocity is going to be about the best you can do unless you are willing to exceed maximum industry pressure.

If one could make a better bullet for the round, and over time with powder advancements accuracy could be improved. However, the round was never designed to be a sub-moa cartridge.

This^ The round isn't a match round and velocity is not always your friend. Right now the round is pretty good if you find the barrel to bullet combination just like any other rifle.
Lipstick on a pig is still a pig.

The best thing you will do to help it will be consistent ammo, better bullets and more consistent powder charges

All of the nicer x39 (Lapua, etc.) is on the slower side.

I understand the question was about 7.62X39.  If you want a nice bump in accuracy consider a 5.45mm AK 

 

The answer is yes and no. If you are using an auto loader like the sks,ak,or ar the answer is no. If you are using a strong modern bolt action then yes you could increase the accuracy and velocity.

I use IMI and PMC brass
Remington 9.5 primers. If you substitute any primers reduce your powder charge, Rem 9.5's are mild primers and produce lower pressures.
OAL 2.190"

24.5 grains of H4198 with Sierra .311" 125 grain Pro-Hunters or Hornady .310" 123 grain SP.

28.0 grains of H322 with the same bullets and OAL listed above.

This load data was the end result of pressure and accuracy testing conducted by C.E. Harris for publication in the NRA "American Rifleman" and republished in the NRA magazine "Semi-Auto Rifles - Data & Comments". I've been using it for over twenty years with excellent results on target.

I have fired 1.5" five shot groups @ 100 yards from a 20" AR-15 chambered in 7.62x39mm using this data.

The 7.62x39 round loves the H4198 powder and it works just as well compressed. If you use the compressed 26.0-26.5 grains of H4198 and pair it with a Sierra Pro-hunter 150gr .311 bullet you will get the best combination of fps and downrange energy with very good accuracy. That's on the condition as a hunting bullet as well as if your gun likes .311 diameter bullets. If plinking and range shooting is your fancy then a good 123gr MatchKing .311 bullet and about 24.5 grain of H4198 might suit you better. Just my 2 cents from research and shooting out of my AR-15 w/16" barrel and a couple cheap SKS's.

I have loaded up some 170gr JSP for my AK and got 2000 fps with AA2520.  But my AK is the NHM-91, and so I was able to work up these loads using a heavy bullet, slow powder, and the longer barrel to some good effect.  Mostly, I just wanted to see what I could push it to, but I also didn't want to beat the snot out of the rifle.  I don't fire that load through it anymore, and stick to surplus/other steel.