The 5.45 is much longer than the 5.56 thus making the tumbling more devastating
I have the aksu in 5.45 and 7.62 and both will reach out to 200y and at that range if you didnt get IMMEDIATE medical attention either round would be lethal...
Just do the math... Force= 1/2*Mass*velocity^2
So given that the 107ur is 1800 fps with a 120g bullet then the energy would be 194x10^6
5.45 is 2625fps with 53gr bullet then the energy would be 182x10^6
This is the energy when it leaves the bbl... and both will drop however the 5.45 will lose energy faster due to its lack of mass I believe.. I Would have to trend chart this to be positive
Dont forget to take into consideration cross sectional area of the bullet and type of bullet
I think your answer lies in what you want to do with the gun.. Heavier bullets are better for shooting through cover and body armor, If your opponent has no armor this is all irrelevant...
Not to mention the AKSU falls under the category of a PDW which was designed to be the same size as a SMG while using a full sized cartridge, so compare any of the 3 rifle calibers to SMG rounds and they come out on top by a long shot.
Quoted from Justinmcmillion
https://www.theakforum.net/threads/compare-krink-ballistics-5-45-vs-7-62.109238/