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. 

EmericD said:

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".

Uh, no.  It cannot also be written that way.  That says something completely different than what I wrote.

20 and 25mm are just whole different form factor than 40mm

You can literally cut down a 50bmg case , flare the neck straight and stick in a 20mm cannon projectile, stick whole thing in a 50BMG action, fit 5 rds in 5rd 50BMG magazine mount a thin walled 20mm barrel. the main effort is then spent to shave weight from .50cal bolt and receiver making them out of aluminum with a steel locking insert for the new low-pressure round. 25mm is not that much larger a magazine similar to those used in 50 bmg would have 4 instead of 5 rounds in it.

Tubular mags for small caliber like that make no sense as capacity is more down to OAL than diameter, OAL is nearly the same for the 20mm vs 40mm grenade , while box magazine  is much more limited by round diameter, Same goes for Milkor style revolver its hardly of much use to these small caliber grenade launchers.  

Form factor changes things in similar ways in rifles and shotguns, first are impractical with tubular mags second are  rarely made with box mags that make them unwieldy or offer even less capacity than tubular magazine