Can anyone tell me what powder is used in the Czechicon surplus 7.62 x 39?

I have pulled bullets from these and weighed the powder. The ones I've weighed so far hold 23 grains.

Just for giggles, I loaded up some Winchester brass with this powder, and found my groups are tighter.

I have been using 27 grains of IMR 4895 which seems to be the slowest in the reloading manual and I'm trying to find out if a faster powder is the route I need to go, and if so, how fast.
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