The main advantages the QJY88 brings beyond the QBB95 are range and endurance.
They might fire the same cartridge and the 95 even have a higher MV, but there is good reason why the 88 is rated as 800-1000m effective range while the 95 is only 600-800m.
The heavier weight of the 88 allows for added stability and controllability at extended ranges, whereas with the 95, even though the rounds can reach just as far downrange, in automatic fire mode, the lighter gun would jump about so much that it would just be a waste of ammo to try to hit someone more than 600m away or something more than 800m away. As such, the heavy weight of the 88 is a feature, not a bug.
The effective range is generally not determined by the stability or mass of the weapon, but rather the mass of the bullet, bullet ballistic coefficient and muzzle velocity. QBB95 and QJY88 may be using the same cartridge, but the powder and bullet masses are different,
. The QBB95 uses a 64 grain (4.15 g) bullet while QJY88 uses a 77 grain bullet. The the cross-section of the bullet are the same so the heavier bullet losses less fraction of the energy per distance traversed and so has a longer effective range, even with a slightly lower muzzle velocity. 5.56 type of rile can also have heavy bullets, such as 77 grain, provided the barrel groove (inches of barrel/rotation, twist) matches the bullet mass for stabilization (yes, a bullet mass has to be matched to the barrel twist for accuracy, bullet may tumble if not stabilized).
The QJY88 has a larger barrel diameter/more mass and so would heat up slower and so first few rounds may be more accurate if you fire semi-auto. Typical assault rife barrel gets hot after 5 rounds while a thicker barrel reach the same temperature after around 10 rounds, but neither of these weapons are meant to be very accurate. Once the barrel heats up the vibration dynamics change and the point of impact changes as well. Heavier barrel is less sensitive to heat up harmonic changes because it is stronger and likely have less change in the point of impact. This may be better effective range by some definition, but effective range also include how much punch the bullet has at the point of impact. Theoretical you can hit someone with the QBB95 round at >1000 meters (such as 5.56 rounds hitting paper at long range), but it won't be able to take the target out since there is no energy left.
