QTS-11 OICW. 5.8 mm Heavy and 20 mm Air Burst.

Insignius said:

I dont think that they would want to sacrifice the flat trajectory in favor for more explosive material. Or else, they can just go with the underslug design that is being thrown around here and cited even in Chinese forums by people who are vehemently against the OICW concept.

What they probably fail to realize is that a higher speed grenade with lower drag and flatter trajectory is a lot more accurate and hence more capable of inflicting critical damage even with lower explosive load. Even with a killing radius of just a single meter, an accurately placed airburst grenade into the firing ports of a defensive position will kill or seriously wound the enemy who is shooting out of it. As long as your explosive charge isnt that of a tank gun or a 1000lbs bomb, accuracy trumps explosive power.

Also, a smaller and faster grenade might also be able to rip through anti-grenade nets set up by the defender to prevent slower thrown or launched grenades to get through firing ports or windows. Airburst function might also be applied here to good effect to counter such defenses.

refer to this info graphic:

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Which is exactly why there's a need for thermobaric warhead option, one shot and the strongpoint with be the defenders' burial mound.

@TerraN_EmpirE: the actual length of, say, the Korean 20mm grenade is longer than the nominal length, and the actual length of the QTS-11 seems longer than actual. In either case, it should be possible to increase the volume of the grenade by extending the length of the ammunition. This would also provide for backwards compatibility as legacy grenades can also be jammed into the chamber, if more range is needed.

Inst said:

@TerraN_EmpirE: the actual length of, say, the Korean 20mm grenade is longer than the nominal length,

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The dimensions of the K11's round are known as is it's weight 20x30mm 100 grams
Although the Chinese have stated a 20mm round they never gave the length of the headspace. however they did give a weight of 85g This is lighter than the Rounds of the old XM29. likely pining at or below that of the XM29 20x28mm.

and the actual length of the QTS-11 seems longer than actual. In either case, it should be possible to increase the volume of the grenade by extending the length of the ammunition. This would also provide for backwards compatibility as legacy grenades can also be jammed into the chamber, if more range is needed.

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jammed into the chamber,
This ^ is the stuff of gun bunny nightmares! If It was not reserved for moderators I would have put it in Blood Red. As is Screaming Emergency Orange will have to do

You have a fixed space between the bolt and the chamber. The bolt and the chamber not the throw space and the Chamber. The bolt has to close properly to fire properly. That's how a bolt action, In fact any firearms action works. you cannot ram a 20x110mm round down the barrel and hope it works. Farther more remember the weight of the system. The Chinese like all makers get that weight by balancing the weight of the materials and strength.
The makers balanced Recoil, Chamber pressures and case sizing to get the system to work reliably. Placing a round not spec'd to "Jamming" the system into the system in the best case, it won't chamber. in second best case it won't work. In the Worst case It will Explode in the weapon destroying the weapon and injuring the shooter.
under loaded rounds can become barrel obstructions which if unnoticed will cause a barrel breach on next shooting, Rounds lacking the right headspace won't seal properly may not seat properly damaging the feed ramps causing a failure down the line. A round with a more than tolerance powder charge will cause excessive wear or even blow the weapon apart.
For a Soldier that means 2 things first he is out of the fight as his primary weapon is gone. remember although the QST11 has a 5.8x42mm portion that portion is linked to the Grenade launcher and if the launcher blows it will destroy the sight, the upper receiver and stock. The barrel will also likely breach right into the chamber of the 5.8mm portion. Unlike the XM29 which might have left a 5.56mm pistol this is a singular system.
Next because it's a bullpup it's going to mean that the shooter is likely hurt. That means that his unit now has reduced effectiveness.

Terran_Empire: my point is in regards to a QTS-11 modified for longer ammunition. That is, you have 20x60 and 20x120 ammo, with the rifle chambered for the latter. You can also stuff 20x60 with accuracy penalties for greater ranged fire, or you can use the 20x120mm for better effect.

The QST11 is a shoulder fired weapon, so you need to balance recoil.
The Neopup is chambered for 20x42mm and that is about the largest a infantryman can really expect to fire from the shoulder.
20x110mm is the round fired by Chainguns and rifles like this.

It's a ballance game. heavier rounds with higher pressures demand longer barrels to get stability. If the Rounds are not Stable, they are not accurate.

Does this look like it's physically 20x42 to you? The 20x42 refers to some element of the round, but the actual dimensions are closer to 20x100.

As to balance; the QTS-11 is a 800m effective range rifle, using a 82 gram projectile with about 2 grams of propellant. An expanded payload munition can sacrifice distance for payload.

When Talking rounds you use the diameter and the headspace not the overall length. the part you want to lengthen faces the issues in the chamber and rifling. A simple grenade launcher like an under barrel can cheat because it only deals a little with that issue. it's more like an old cannon or mortar. but nce you start with higher velocities how it sits in the barrel and chamber and bore all become critical.
The rounds you pictured are 20x42mm for a Truvelo CMS and the Denel PMP Inkunzi but notice something about them they are all about the same lengths. you cannot safely cram a round into a weapon beyond its intended envelope.

TE: my point is that you mod the QTS-11 to support longer rounds. You are correct when you can't cram a round beyond its intended envelope, but you can cram a round before its intended envelope; i.e, older rounds are used for long-range shooting, while newer rounds are used for short-ranged shooting. You only need to double the grenade mass to match the mass of an UBG grenade, since the latter tend to be underpowered.