XM25 "good enough"

[Fuchs]

The UBGL is essentially an (almost) always ready-to-fire version of WW2-era rifle grenades that used muzzle cups (such as German Schissbecher).

Modern rifle grenades are descendants of those WW2-era rifle grenades that used a rather stokes-like principle (sitting on the muzzle).


The UBGL and stnad-alone GL designs add (just like the Schiessbecher) a certain fixed cost of mass. No matter how many grenades you carry, you gotta carry those 1-4 pounds of weapon.

Thus we have today the choice between
* rifle grenades with zero fixed costs (mass) thanks to ladder sights on the grenade itself
OR
* grenade launchers with fixed costs (mass), which in present GL designs is somewhat outweighed by less slow use (I wouldn't say 'quick' as long as you need to flip up sights or carry a carbine in ready position but have to switch to a stand-alone GL). The variable costs (mass per shot) is also smaller.

Recoil as a problem rather favours rifle-attached solutions, for the additional weight reduces felt recoil. A given warhead mass and a given trajectory (~muzzle velocity) will yield about the same recoil all else equal (weight and thus recoil differences between fin and spin stabilisation may occur, though).


In the end, today's rifle grenades have two niches:

(1) Whole small unit grenade salvo without many heavy GLs
(2) Large calibre grenades (see the Simon doorbreacher rifle grenade)

GLs have other advantages

(1) Potential exploitation of Medium-low pressure principle.
(2) Can be carried ready for fire in UBGL
(3) Can be a multi-shot weapon (revolver or pumpgun principle usually)
(4) already standardised
(5) No need for bullet trap or special ballistite blank cartridge
(6) Can be used on weapons of different calibres without aiming issues
(7) The limitation to few soldiers inherently leads to higher practice standard by specialisation in practice
(8) Propellant power is independent of rifle/carbine calibre and barrel length.

The French, Israelis and some other countries make still much use of rifle grenades.

[Firn]

The UBGL is essentially an (almost) always ready-to-fire version of WW2-era rifle grenades that used muzzle cups (such as German Schissbecher).

Modern rifle grenades are descendants of those WW2-era rifle grenades that used a rather stokes-like principle (sitting on the muzzle).


The UBGL and stnad-alone GL designs add (just like the Schiessbecher) a certain fixed cost of mass. No matter how many grenades you carry, you gotta carry those 1-4 pounds of weapon.

Thus we have today the choice between
* rifle grenades with zero fixed costs (mass) thanks to ladder sights on the grenade itself
OR
* grenade launchers with fixed costs (mass), which in present GL designs is somewhat outweighed by less slow use (I wouldn't say 'quick' as long as you need to flip up sights or carry a carbine in ready position but have to switch to a stand-alone GL). The variable costs (mass per shot) is also smaller.

Recoil as a problem rather favours rifle-attached solutions, for the additional weight reduces felt recoil. A given warhead mass and a given trajectory (~muzzle velocity) will yield about the same recoil all else equal (weight and thus recoil differences between fin and spin stabilisation may occur, though).


In the end, today's rifle grenades have two niches:

(1) Whole small unit grenade salvo without many heavy GLs
(2) Large calibre grenades (see the Simon doorbreacher rifle grenade)

GLs have other advantages

(1) Potential exploitation of Medium-low pressure principle.
(2) Can be carried ready for fire in UBGL
(3) Can be a multi-shot weapon (revolver or pumpgun principle usually)
(4) already standardised
(5) No need for bullet trap or special ballistite blank cartridge
(6) Can be used on weapons of different calibres without aiming issues
(7) The limitation to few soldiers inherently leads to higher practice standard by specialisation in practice
(8) Propellant power is independent of rifle/carbine calibre and barrel length.

The French, Israelis and some other countries make still much use of rifle grenades.

I mostly agree with this summary.

It is interesting that early post-WWII AT rifle grenades shared the technology, warhead or even more parts with the missiles fired by rocket launchers. This goes for the French (AC58 - WASP 58), Swiss (Gewehrgranate 58 - Raketenrohr) and the USA (M31 HEAT - LAW72).

For direct fire the max. effective ranges seem to have been around 75 to 100 m. Used like spigot-mortar with rocket-boosted grenades ranges up to 550 m, although shorter ranges would have been the norm. Velocities of up to 75 m/s were achieved, but with 7,62 mm blanks and as said with a rocket boost. Not much compared to the claimed 250 m/s of the Wasp and still a lot slower than the 145 m/s of the LAW72.

The Swiss army used the training rifle grenade 58 to lay cable across obstacles, something which was already done in WWII.

All in all I could imagine those niche uses ( points taken partly by Fuchs) with modern assault rifles.

(1) Whole small unit grenade salvos (HEDP, etc)**
(2) Large calibre niche grenades (SIMON, smoke grenades)*
(3) Cable, Grapple, Cordex projector


All of them should be bullet-trap or -through types. If practical, the lighter rifle grenades (HE/HEDP) could also double as defensive handgrenades, like some German WWII ones.

*Heavy AT grenades don't seem to make sense enough compared to light rocket launchers like the LAW72 to develop, train and carry them.

**Light mortars have taken part of that role, even if the rifle grenades are of course a different kettle of fish.

P.S: I guess Schissbecher is a typo

[Fuchs]

Some typos happen unconsciously, but honestly...

It was a stupid design, about as much over-engineered as the 5 cm leGrW 36 (platoon mortar). German engineers of the 30's were totally in love with spin stabilisation and neglected fin stabilisation (see also Rz 65, Nebelwerfer 41).

This, by the way, enabled the 8th air force to use its quite poor heavy bomber designs (which were mere target practice for fin-stabilised low-tech R4/M rockets!) in the first place.

[Compost]

XM25 could be “good enough” for use in some kind of adventure park but virtually useless everywhere else. See post 928 on Roles and Weapons with the Squad.

In the end, today's rifle grenades have two niches:

(1) Whole small unit grenade salvo without many heavy GLs
(2) Large calibre grenades (see the Simon doorbreacher rifle grenade).

That first niche would require prompt supply of spare rifles, carbines and attachments to replace those damaged or wrecked delivering volley fire during operations, and earlier in range practice and field exercise ?

What useful niches (other than salvo line throwing) are left when a section/squad typically has hand grenades, UGLs and demo charges plus Armbrust, M-72 or suchlike; and when a modern platoon can have a 60mm handheld mortar (issued or attached) and also one or more 40mm MGLs ?

[Compost]

It has been pointed out that lack of calibre makes for confusion. Can sentence be corrected?

[Fuchs]

GLs have other advantages

(1) Potential exploitation of Medium-low pressure principle.
(...)

I am disappointed. Why did nobody point out that rifle grenades inherently kind of exploit the high-low pressure principle?

------------------------

@Compost: Why should a salvo of rifle grenades wreck the weapons? The rifle/carbine is largely unaffected by the use of rifle grenades.

UBGLs and MGLs will typically not be together in a small unit. 40 mm medium velocity ammunition also puts a bold question mark behind a platoon ("commando", "light" or "patrol") mortar since it has ~700 m range and enough physical effect to achieve similar psychological effect.

[Compost]

Compost: Why should a salvo of rifle grenades wreck the weapons? The rifle/carbine is largely unaffected by the use of rifle grenades..

First, “bullet-trap or –through designs” produce a pressure pulse that is higher than the normal pressure for which the rifle or carbine was primarily designed. For grenade launching to be approved that higher pressure must be within safety limits. Perhaps that also means there are no cumulative affects and my residual concern there is wrong.

Second, the user expects the recoil to be higher and anyway to achieve range a recommended method of firing is with the butt grounded. If/when the weapon is held down with inadequate pressure – especially against a hard surface – the butt is liable to damage together with any frangibles attached to the weapon. That is likely to occur due to haste and stress during operations and exercise and training. An expert is unlikely to make that mistake but in volley/salvo fire only some will be rifle grenade experts.

UBGLs and MGLs will typically not be together in a small unit. 40 mm medium velocity ammunition also puts a bold question mark behind a platoon ("commando", "light" or "patrol") mortar since it has ~700 m range and enough physical effect to achieve similar psychological effect.

Agree UGLs and MGLs and mortars will typically not all be together in a small sub-unit such as a section/squad but at least two of the three are on issue to some modern platoons. The USMC platoon now has one or more MGLs and its squads have UGLs able to fire LV and MV rounds.

However, a light mortar is longer ranged than 40mm MV weapons and can launch a significantly heavier and more damaging weight of ‘munitions’ particularly including HE, line, smoke and exotics such as para-cameras and micro-UAVs. If a light mortar is needed by a USMC platoon then a 60mm can be obtained from the company weapons platoon.

Hence my phrase: “when a modern platoon can have a 60mm handheld mortar (issued or attached) and also one or more 40mm MGLs “.

In line with that concept, the Br Army platoon has regained a light mortar and its sections have UGLs. I believe that 60mm mortar would be carefully kept on issue (although not invariably carried on light infantry operations) even if the platoon were to gain one or even two of the increasingly attractive 40mm MGLs.

[Fuchs]

This is the very first time that I hear about some "pressure pulse" problem associated with rifle grenades. I have some physics skills, but I can only imagine a tiny effect after the time when the bullet reaches the muzzle. The grenade might act as a cloture (hardly with bullet-thru, though) for a very, very short moment.

I doubt that this has any measurable effect, since barrels have a decent safety margin anyway.


About the buttplate damage; again entirely new to me. Soldiers do a lot with their rifles and rifles have to be tough anyway. The recoil of a rifle - even with a heavy projectile - should be well within the limits of normal harsh treatment.

[Ken White]

The only problems with rifle grenades is that they are heavy, inaccurate and tie up the rifle from which they're fired. Due to those shortfalls, they are disappearing from inventories and rightly so. A 40mm under a rifle is a far better solution.

Whether the XM-25 is going to be a plus for combat -- heavy combat -- remains to be seen. For combat operations like the current efforts, it does what it's supposed to do -- which is more than can say for most of the tripod or vehicle mounted AGLs. Those things are significantly overrated. Though they are fun to play with...

Last I heard, Canada proposed to replace their 60mm mortars with 40 AGLs. I hope, for their sake, that's not true...

[Kiwigrunt]

This is hearsay but I was led to believe that the NZ army tested rifle grenades prior to adopting the 203 and the recoil would rattle the AUG to bits. I have read suggestions regarding the British CLAW of the nineties knocking the SA80 scope out of zero. But the 203 is said to do that to the standard scope on the AUG as well, although I never experienced that.

The French, long-time users of rifle grenades, also seem to be moving towards UGLs.

[Compost]

This is hearsay but I was led to believe that the NZ army tested rifle grenades prior to adopting the 203 and the recoil would rattle the AUG to bits. I have read suggestions regarding the British CLAW of the nineties knocking the SA80 scope out of zero. But the 203 is said to do that to the standard scope on the AUG as well, although I never experienced that.

The following paras on rifle grenades summarize what I have been told/instructed and read over time combined with some assumptions. (Due to ignorance, the affects of gas being bled off into the cylinder during the grenade launch is largely ignored.)

Launch of a bullet-trap or bullet-through rifle grenade does include some energy simply transferred from the bullet to the grenade. However, the grenade is mainly projected by gas and that is the basic reason for the higher recoil force.

Depending on the configuration of the muzzle and/or projector, the rapidly expanding jet of gas driving the bullet out of the barrel may be initially directed upon the whole or only part of the driving surface of the grenade. Whole exposure (in a chamber with a cross-section larger than the bore) or partial exposure increasing to whole exposure as the grenade moves forward would seemingly be accompanied by a reduction in the gas pressure which was until that moment restricted to the bore. However that reduction can be almost instantaneously overtaken by an increase as the continued expansion of the gas jet is restrained by the slowly accelerating grenade.

Rifle ammunition is designed to burn propellant to initiate the movement of a bullet and spin it up to achieve a particular muzzle velocity. Irrespective of whether the propellant is fast- or slow-burning and whether that propellant is exposed and burnt at a uniform or an increasing or reducing rate, the bullet is started and accelerated by varying pressures of gas. Typically a gas pressure peak is generated early during passage of the bullet up the barrel and the bullet is stabilised although it can still be accelerating as it exits the muzzle due to an ( ‘extinguished’ or still-burning) gas jet that continues to operate but at a lower pressure than lower in the bore. To avoid violent operation of the bolt unlocking mechanism and of the bolt itself, a rifle and its ammunition are designed so that pressure in the barrel has been somewhat reduced before any gas reaches a tapping port into a recoil cylinder.

A particular feature of the rifle grenade is that it introduces another pressure peak and also adjacent high pressures that all occur close to the muzzle. Dependent upon grenade weight, that second pressure peak can be higher or much higher in a rifle than the ‘normal’ pressure peak produced when firing a single round of ball ammunition.

The time span during which the grenade-related pressures operate can be referred to as a pressure pulse. In a short-barrelled carbine that second peak will tend to reach a higher pressure and consequently duration of the pulse will be reduced.
All gas pressures generated in the barrel are also directed backward to the firing chamber and via the bolt to the bolt locking mechanism. If the intended use of a rifle or carbine includes the firing of rifle grenades, then the bolt locking mechanism must be more strongly engineered. That applies especially to the lugs of a forward locking bolt, and the receiver that houses a rear locking bolt

Additionally the second peak and adjacent pressures occur as gas is being tapped from the barrel to drive the bolt-unlocking cycle. To avoid violent unlocking it is preferable to suspend or reduce gas tapping. For example the gas regulator of a 7.62mm FAL/L1A1 SLR was routinely adjusted to close off the gas cylinder before firing a ballistite cartridge to launch an Energa AT grenade. Failure to close off often resulted in a bent piston rod.

My books on ballistics and small arms are currently packed in boxes, and this topic will be long gone before they are unpacked. So am interested to read any post that identifies an authoritative and readily accessible source, or provides detail that expands on or contradicts the above.

But in summary there is at least one good technical reason to avoid use of rifle grenades.