My thoughts about fragmentation are exaclty as yours!
Unfortunately I’ve not possibility to direct to you some of these rounds right now, but I’ll think about that. I hope I’ll have a possibility to post some additional info about the round and bullet soon.
I’m not agree with you - some FMJ no matter RN or pointed with thick jacket or hard core did not fragment in soft tissues (like the bullets of AK47/74 for instance) and yes, their primary wounding effect occurs when they begin to tumble and reach the point of traveling sideways, the transfer of their energy is much rapid (and thus causing greater temporary and permanent cavity), than when traveling point or base forward (bigger interaction surface), but did not disintegrate upon passage through the soft tissue.
But that is not the case with M193 or M855 - upon impact they begin to tumble as abovementioned non-fragmenting bullets and when they reach the point of traveling sideways, when they possess enough velocity (energy), they can’t withstand the tension and usualy break up in the area of the cannelure and after that, in dependence of residual velocity (energy), nose section usually travels on its own path, and the rear section of the bullet either fragments further or remain relatively intact, but forms different wound channel than that of the nose part.
Look at that artickle by Martin L. Fackler:
This subject is also of interest:
Take care and have fun!