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Garry, the performance of the milspec ammo can be improved a lot by calling CZ and requesting an overpower firing pin spring. The stock spring is marginal on hard primers and gives inconsistent ignition. The milspec ammo still ain't very good, but changing springs and graphiting the spring, firing pin, and bolt interior more than halved my groups.
I went through much the same process you did, and got the same results. The 150 grain Sierra .311s give the best accuracy and the most downrange energy. Sierra can tell you the remaining velocity needed for expansion, but my best guess is that it is marginal at 150 yards. I'd expect some expansion on a shoulder shot and none on a ribcage shot.
The bullets built specifically as game bullets for the 7.62x39 are a lot more likely to expand, but I have my doubts about their pentration at 150 yards.
Interestingly, I am getting superb cast bullet performance from my CZ 527. Lee's C312-155-2R weighs 159 grains with my alloy and gives about 1.5 MOA at 2200 fps. I'm strongly tempted to use that bullet with annealed noses on any hunting I do.
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