You seem to be missing the point:  Despite the supposed advantages of fixed, tube magazines being touted by some in this thread, pretty much every multi-shot grenade launcher developed during the last two decades uses detachable magazines.  It doesn't matter that a drum or box magazine can't be "topped off" and may weigh as much as two or three rounds of ammo, it's still seen as a superior feed system versus a shotgun-style tube.

Pointless to argue , there were at least 5 designs developed with tubular mag one time or another so it seemed promising enough to try , GM-94 , ST Kinetics SSW, Bofors SSW ,Metal Storm 3GL ,Arcus 40, and there are hardly many more box feed grenade launchers in 40mm caliber so its a bit hard to claim box mag rules them all , and as none are in use it's a moot point anyway?

At present is seems Milkor ,GM-94 and the Chinese Grenade launchers are only ones in wide service .

We can't put the 25-20mm grenade launcher concepts developed in the past into the same category, they are closer to a low pressure 50BMG rifle than 40mm GL , and even these more or less failed to enter service.

40mm GL 5rd box mag is at least 1+kg , equal to 4-5x 40mm grenades ( each weighing 190-230g) , so its not that trivial considering that soldiers' combat ammo load is typically in the range of 3-3,5kg

The problem seems to have its roots in the shape of the 40 mm catridges. Its simply no where near optimal for any feed system.

IMHO this is why the results of trying to get a multi shot 40 mm GL are all underwelming.

A clean slate approach seems the most promising course of action in this case. 

Mr. T (MrT4) said:

...there were at least 5 designs developed with tubular mag one time or another so it seemed promising enough to try , GM-94 , ST Kinetics SSW, Bofors SSW ,Metal Storm 3GL ,Arcus 40, and there are hardly many more box feed grenade launchers in 40mm caliber so its a bit hard to claim box mag rules them all...

1.  I clearly stated that I was talking about weapons developed during the last two decades.  The GM94 and Bofors SSW are 20th century designs, and so do not count.  And the 3GL does not even have a magazine; the rounds are all loaded in the barrel.

2.  I never limited my remarks to grenade launchers only in 40mm caliber.  You are trying to make it sound like I said something different than I actually did.

3.  Again, I never claimed that "box mag rules them all."  What I repeatedly said is that most development has been on grenade launchers with detachable drum or box mags.

Mr. T (MrT4) said:

At present is seems Milkor ,GM-94 and the Chinese Grenade launchers are only ones in wide service .

Again, I was addressing what has been designed and developed, not what has been adopted and fielded.

Mr. T (MrT4) said:

We can't put the 25-20mm grenade launcher concepts developed in the past into the same category [as the] 40mm GL...

I strongly disagree.  There is no fundamental difference between 25mm and 40mm grenade launchers.  Both are designed to fire bursting munitions.

25mm HEAB - https://youtu.be/w-w_oNouMWo?t=57

40mm HEAB - https://youtu.be/BPaC1LTrHy0?t=545

schnuersi said:

The problem seems to have its roots in the shape of the 40 mm catridges. Its simply no where near optimal for any feed system. IMHO this is why the results of trying to get a multi shot 40 mm GL are all underwelming. A clean slate approach seems the most promising course of action in this case. 

Does anyone use the Czech RAG-30? a 5-round top mounted box magazine, chambered for the standard Russian 30mm long-range grenade. It's been around for years.

http://www.czechweapons.com/en/rag-30/

Not to my knowledge.

While the 30x29B has a somwhat better shape compared to 40 mm grenades its a HV grenade and as such unnessecarily powerfull. This probably Limits the appeal of the RAG-30.

To get an attractive multi shot weapon system it seems that grenades with the smallest possible diameter of comparable weight and effect of a 40 mm grenade is developed. The MV needs to be tailored so the system is still usable from the shoulder unsupported.

 The XM 25 Tool that route but they got the balance wrong, grenade to light but fast, and focussed to much on the airburst feature.

A more sensible approach would be to design the grenade with the desired effect to potentially replace 40 mm first. Design a multi shot launcher for it. Design an airburst system for the weapon and ammo last.   

The obvious solutions to the recoil problem would be either:

1. To produce a lower-velocity version of the 30 x 29B ammunition (modifying the case belt to ensure that the HV loadings would not chamber)

2. To combine a very short barrel with a very long muzzle brake (not so comfortable for anyone near the shooter!)

autogun said:

2. To combine a very short barrel with a very long muzzle brake (not so comfortable for anyone near the shooter!)

Due to the low muzzle pressure of launched grenades, muzzle brake are not very effective. That was the problem with the Barrett "payload rifle", the recoil was brisk and can't be mitigated with a muzzle brake.

stancrist said:

You seem to be missing the point: Despite the supposed advantages of fixed, tube magazines being touted by some in this thread, pretty much every multi-shot grenade launcher developed during the last two decades uses detachable magazines.

Which could be also written this way:

"You seem to be missing the point: Despite the supposed advantages of box magazines being touted by some in this thread, the only multi-shot grenade launcher adopted by a western army during the last two decades uses a revolver action".

schnuersi said:

The problem seems to have its roots in the shape of the 40 mm catridges. Its simply no where near optimal for any feed system. IMHO this is why the results of trying to get a multi shot 40 mm GL are all underwelming. A clean slate approach seems the most promising course of action in this case.

I actually think Rheinmetalls 40x51 is a pretty smart approach. It uses the same 40x53mm grenades used in the grenade machine gun, but fired at a tolerable 100m/s for shoulder launched use.

This is nice because

-The ~240g grenade of the x53 has proven to have pretty decent punch / about as much bang as we could expect from a shoulder fired grenade launcher; at the same time we probably dont want to go much lighter in shell weight

-Having x51MV and x53HV use the same shell allows for a much better economy of scale for the production of high performance fragmentation / airburst shells. 

-100m/s velocity allows for better range, but still maintains plunging trajectory for better attach against trenches / better effect with base fused forward fragmenting shells. 

-Certain types of x51 launchers would remain backwards compatible with existing warstocks of 40x46mm

....

Frankly 40x51 is what a smarter OICW program would have produced.