QBU-88 uses dedicated heavy round with slower muzzle velocity but higher muzzle energy than standard round for QBZ-95.
The new DMR may use dedicated heavy round or the new all-purpose round which has muzzle energy higher than both the heavy round and standard rounds.
It is not the velocity along but the energy that count the lethality. Of course larger caliber is better, but DMR is not true sniper, it is meant to share ammunition with squad members, so sacrificing is a necessity.
QBU88 for quite some time was used as sniper rifle but it looks like they now use the CS/LR4 as their good-and-proper sniper rifle. Actually, given that they now showcase the CS/LR4 at the military museum in Beijing (I just came back from Beijing, took some pictures of that place), as well as debuted it on CCTV several times, think that's their sniper rifle now and QBU88 will be used as DMR exclusively henceforth...though it still has a reputation problem to overcome.
Hmm I feel like despite the ambidextrous fire selector, this rifle is still designed to be used on the right hand optimally.
On pictures of the rifle's right side I can't find a similarly positioned bolt release.
Meanwhile, the mag release lever with the tab on the right side that you mention, IMO could be there to assist a right handed shooter's operation of the lever?
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The new AR series shown in the parade is probably what we known as carbine, the full length barrel as well as DMR has yet properly debuted but I think it could be "soon", alas the rifles still sporting the company logo, thus those are still probably in troop trial phase.
The latch at the front of the trigger guard is most likely magazine release latch, so we may see them go fast mag change, AK style - heck, the setup is probably fully compatible with AK-reolad drills! Though I wonder what the mechanical operation would be...the layout sort of AR15-ish, or else they could go fo folding buttstock instead of telescopic one.