Cool, you used the model 74 instead of the 47 or the AKM; the 5.45x39mm is just a modified 7.62x39mm cartridge necked down to .221 caliber (5.61mm). There are some differences between the .223 remington cartridge and 5.56mm NATO as well as between .308 Winchester and 7.62 NATO despite their case measurements being identical.
In the case of the first two, the NATO round uses a heavier 60gr projectile compared to the 55gr used by .223 Remington, the bullet is longer resulting in a slight difference in overall cartridge size and NATO rounds need a tighter rifling twist (1:178mm) than .223 remington does (1:305mm).
Some weapons are now produced with a compromise rifling twist figure that achieves good performance from both rounds.
The .308 and 7.62mm NATO have identical measurements but they use different primers, other than that I am not sure if there are other differences, maybe Colt knows.
And finally regarding the Desert Eagle, it has never been produced in .400 Corbon to my knowledge; .400 CorBon is only a short autopistol round (10x23mm), most magnum rounds have a longer case of approximately 33mm. There was a model of the DE produced in .41 Magnum but it failed to achieve any success and it was later discontinued.