gatnerd said:

I think the issue with Rifle Grenades is one of accuracy. How accurate are they, and how many RG's will a rifleman ever fire to be able to get combat accurate with one?

This also is an intresting question.
I think it not only depends on the ballistics (trajectory, accuracy) but also on payload. How close to you have to get to achieve effect.
During WW2 the German rifle grenade launcher was considered to be accurate and effective. From all acounts it has been a pretty popular weapon. The GL-attachment was concidered a general piece of equipment and every soldier was trained with it. Although it seems in practice usually a dedicated grenadier used it.
As a side not the sight was considered so useless that it was common practice to shoot the GL just by guessing and pointing. Which according to records was easily done with a "litte" practice.
The standard HE grenade had a diameter of 30 mm, weighted 0,288 kg, 30 g explosive payload and was launched ~65 m/s. Since the grenade is heavier compared to 40 mm LV but has a comparable explosive payload maybe the fragmentation was better giving a larger area of effect resulting in the accuracy being concidered acceptable or good?

schnuersi said:

As a side not the sight was considered so useless that it was common practice to shoot the GL just by guessing and pointing. Which according to records was easily done with a "litte" practice.

I've got a fair bit of experience with low velocity, high trajectory shooting. I used to build 'air cannons' for several years when I was a teenager, out of PVC pipe pressurized to 100psi. They could shoot a potato through a piece of 10mm plywood, and launch little PVC darts 500 yards. It helped that I lived directly next to a hardware store at the time.

Since the pressure was constant, and projectiles fairly uniform in weight, accuracy was surprisingly good - when in the 'zen' state of predicting high trajectory. I once hit a paint can on my first shot at 75yds standing - while holding over the can by several feet. I could just 'feel' that I was on target.

But when not in that zen state, accuracy could be wildly off base. Especially as distance increased.

I recall shooting at a bilboard sign down the street about 200yd that had an anti smoking PSA on it (was a fan of smoking as a teen.) A billboard is huge, but my elevation estimate was tremendously off. Ended up putting a potato through a guys open convertable roof who was driving by - I was 50 yards short and 50' low from my estimates. Needless to say that was the last attempt at that particular target.

Now a rifle grenade is going to be more accurate than a smooth bore potato launcher - but I suspect it would be a lot closer to a potato then a rifle bullet in terms of hit probability. 

I think any of these man portable HE launchers - whether they be 40x46, x51, rifle grenades, 60mm comando mortars, or RPG/Recoiless type launchers - really need some type of 'smart scope' to make maximum use of the limited number of rounds and small warheads. 

And some fun video of rifle grenades against a 'tank' target at what looks to be 40-50m:

YouTube

Teaser: Dale shoots a tank with a Scary Flying Carrot of Doom (Swiss training rifle grenade)

A teaser for some upcoming content: our friend Dale demonstrates a fairly slick "Achtung Panzer" drill, switching a Swiss Sturmgewehr 57 from ball ammunition...

And a very nice history of Swiss Rifle Grenade history and doctrine. The use case seems to primarilly be emergency tank/vehicle defense within 50m, rather then 100-400m anti personell.

YouTube

SWISS FLYING CARROTS: Stgw. 57 Rifle Grenades (Part 1/2: History)

Dale takes us through the historical background leading to the Swiss Sturmgewehr 57 rifle grenade series, starting from the WW2 and post-WW2 perspective. In ...

gatnerd said:

I think any of these man portable HE launchers - whether they be 40x46, x51, rifle grenades, 60mm comando mortars, or RPG/Recoiless type launchers - really need some type of 'smart scope' to make maximum use of the limited number of rounds and small warheads.

We propably can assume that it is generally accepted that the effectiveness of any weapon increases with the sofistication of the aiming system.

How much is needed for a given weapon system to be concidered effective is another question.
The ladder sight of the HK 69, the GL used by the German Army, since the '70 is generally concidered to be usfull and adequate by the users. I can remember GraPi sniping sessions on the shooting range. Consitenly hitting a standard rifle target at 300 was absolutely doable. No zen, no voodoo just competent use of the sight.

schnuersi said:

Consitenly hitting a standard rifle target at 300 was absolutely doable. No zen, no voodoo just competent use of the sight

I'm sure that is the case at a target range.

Id question how repeatable that is against targets of an unknown, irregular distance, where the shooter has to eyeball the target distance and adjust the sight accordingly. Especially if the target involved is higher or lower then the shooter.

The Milkor sight is calibrated in 25m increments, which means that the shooter has to be able to eyeball judge distance within 25m to achieve a hit. That takes a very refined eye to judge distances that well.

gatnerd said:

Id question how repeatable that is against targets of an unknown, irregular distance, where the shooter has to eyeball the target distance and adjust the sight accordingly.

Range guessing is allways a propblem. Even for rifle and MG shooting.
The difference is the impact of a grenade is much easier to spot.

My point was that even ladder sights do work. If the squad leader has a range finder or is good at guessing he can give the information to the grenadier who sets his sight accordingly and puts the grenade on target.
The grenadier doesn'T need a sofisticated sight. He just needs range information.

gatnerd said:

Especially if the target involved is higher or lower then the shooter.

This also is a problem for all small arms. This can only be overcome with training.

This BTW is where rifle grenades shine. Training grenades are usually reusable. It only requires launching cartidges. So training is rather cheap, simple and safe.

schnuersi said:

Range guessing is allways a propblem. Even for rifle and MG shooting. The difference is the impact of a grenade is much easier to spot.

Sure, ranging is important for those weapons at longer distances. But the average rifle can hit a mansize target without any sight adjustment easily at 300m-400m. Hell, I can shoot my Glock against a mansized steel target at 100m with 7/10 accuracy. 

The trajectory of a 40x46mm grenade by comparison is so extreme that a hit against a building cannot be assured from 50m if the trajectory is off - this marine puts his first round right into the road in front of him instead of the building across the steet:

https://www.youtube.com/watch?v=hvEmOJSoJOk

At 200m, the 40x46mm needs 10m elevation over the target:

I believe Emeric had the exact specs in his GPC paper? Listing the allowable ranging error at various distances for 40mm to put the round within lethal frag range? I recall the allowable aiming error being shockingly tight. 

...

The average rifleman might carry 2-3 rifle grenades? That doesn't leave a lot of spares for correcting aim if the first shot is off.

gatnerd said:

The trajectory of a 40x46mm grenade by comparison is so extreme that a hit against a building cannot be assured from 50m if the trajectory is off - this marine puts his first round right into the road in front of him instead of the building across the steet...

That video illustrates your point very well, but I would note that the target is the automobile, not the building.

1st round hit ~5 yards short of the car.  2nd round was ~10 yards over.  3rd round hit just below the car door.

Not a fan of rifle grenades, 40mm is already pushing it with regards to the compromise of number of rounds carried while still having some minimally useful effect on target.  Besides, you should be running suppressors anyway.

IMO, LAW, 40mm MV bounding HE-PFF (not LV HEDP), lightweight suicide drones and/or pike are where its at for individual HE beyond hand grenade range IMO.

With regards to rifle grenades and 40mm, one should assume you will need at least one if not more follow up shots either route you choose.  While the rifle grenade has a larger warhead, it is physically larger and heavier, and you have lower accuracy, lower range (particularly as 40mm MV starts to become more widely adopted), and fewer attempts. Does the larger warhead compensate for this? Perhaps, but I suspect not given most countries have switched to grenade launchers.  Proximity for airburst would certainly help, or even a scaled-up bounding function (which would be simpler and cheaper).

Despite it's smaller casualty radius, IMO the average soldier is more likely to get a 40mm MV close enough to a target to be effective, and since you can carry significantly more ammunition you get more attempts. 

The point of something like MGL (or this critter in the original post) is that you can complete your engagement (including adjusting fire) before having to reload, and even more useful, you can keep your sight picture throughout the engagement (unlike with single shot 40mm and rifle grenades) making finer adjustments easier.  This probably shines even more against fleeting targets of opportunity, like soldiers or vehicles darting across streets in urban terrain.  I would like to see MGLs at squad level (ideally fireteam level, with multiple per squad, but keep in mind I also prefer 5-6 man fireteams)

So, IMO, a soldier with a typical loadout of 40mm grenades should have more stowed kills than the same soldier with rifle grenades.  The larger ammunition load for the 40mm still isn't really as much as I'd like, but I'd be loathe to go smaller. Despite that, it does start getting into the relm of making reconnaissance by fire viable, while you might want to conserve your fewer rifle grenades for known targets... if you weren't using them quickly to break contact or dump weight on the already overburdened soldier.  My guess is a detonation near your position by either would be sufficient to get your undivided attention.

Speaking of overburdened soldiers, I do like the idea of 60mm commando mortars at platoon to compliment the platoon machine guns despite not being a fan of the arguably similar rifle grenades, but you'd almost certainly have to have everyone in the platoon carry a round or two.
 

The table at the end of this article   ( https://www.quarryhs.co.uk/GRENADES%20WEB%20ARTICLE.pdf ) provides some basic comparative stats.

Note that the cross-over point in system weight between 40mm rifled grenades and rifle grenades (ammo plus launcher) is about ten rounds.