I intend on using this rifle for deer hunting in the 25-150 yard range
The vital (heart/lung) area of the average deer is 10-11 inches. Play with some free on line ballistic charts for your bullet and velocity to get a drop chart.
Study the chart until you find a zero where the shot would be no higher the 5 inches and drop no more then 5 inches.
That should tell you where to zero the rifle.
Don't take these number for gospel. I don't own a 7.62X39. I just use the 123 grn bullet at 2300 fps and a sight height of 2.5 inches and plugged the numbers into SHOOTER on my phone.
Sighting in the rifle at 225 yards it will be 4.9 inches high at 150 yards and 5 inches low at 280 yards.
I believe in sight the rifle in at the distance you want in your zero, in this case I would sight it in at 280 yards.
But for info a 280 yard zero would put your round 1/10th of an inch low at 25 yards.
Again don't take these numbers a FACT, I don't know your bullet, its velocity or the sight height above your bore. But if you have that info, you can get pretty close.
If you are sure you wont be hunting past 150 yards, I'd shrink that 10-11 inch vital area where your zero would be somewhere short of 150 yards.
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EDIT: Don't get hung up on energy. Different bullets work different ways, meaning some are designed to come apart disturbing the nervous system of the critter, some are suppose to mushroom to a point and hold together. Both require a X velocity. Find a bullet that is designed to work at your retaining velocity at your target.