Max Effectiveness of 7.62 x 39

[35 Whelen]

That is simply not true. Above a certain velocity, I think around 2600 FPS human tissue cannot yield fast enough, therefor energy is transmitted as if the tissue were solid rather than soft. Much like a boat going on plane when water cannot be displaced rapidly enough and the boat rides on top. The result is energy is spread over a wider area causing more tissue damage than a bullet below that velocity threshold. There is a reason that you are told that velocity and energy don't matter.
Of course, bullet construction is important. Of course, the modern slower heavier more stable 5.56/223 are not as devastating as the old slow twist higher velocity as mentioned. Still I have seen the difference between .223 soft points and 7.62x39 soft points deer hunting. The .223 does definitely do more damage.

Oh boy....here we go again.

 

[Bfh_auto]

That is simply not true. Above a certain velocity, I think around 2600 FPS human tissue cannot yield fast enough, therefor energy is transmitted as if the tissue were solid rather than soft. Much like a boat going on plane when water cannot be displaced rapidly enough and the boat rides on top. The result is energy is spread over a wider area causing more tissue damage than a bullet below that velocity threshold. There is a reason that you are told that velocity and energy don't matter.
Of course, bullet construction is important. Of course, the modern slower heavier more stable 5.56/223 are not as devastating as the old slow twist higher velocity as mentioned. Still I have seen the difference between .223 soft points and 7.62x39 soft points deer hunting. The .223 does definitely do more damage.

A lot of this is dependent on the bullet. A heavy for caliber 50/50 COWW/ PB bullet pushed at 7.62x39 velocity does more damage through both shoulders of a deer. If you compare only the entrance side. The 5.56 does more.
If you compare on things like opossums or feral cats. The 5.56 does way more.
If you're shooting jacketed bullets in 7.62x39. You need a special bullet to optimize performance. Kind of like 300 BO.
I consider all three to be adequate for about 150 yards. Beyond that I want more energy. But it's just my personal opinion.

 

[Robert]

6 pages of what 7.62x39 vs X is plenty. We can pick nits all day long but at this point we are going in circles. Let's call it a day.