XM25 "good enough"

[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.

[Fuchs]

Keep in mind that you do not need to use heavier rifle grenades than barrel-launched grenades, and you don't need to use them at a higher velocity.

FN Bullet-thru: 320 g
40x46mm: 230-250 g

This means all higher recoil would quite by definition be an intentionally accepted by-product of higher performance.

[Compost]

Air-burst 40x53mm HV cartridge grenades and integrated FCS-fuzesetters are already available for several types of 40xmm AGLs.

A recent report claims the USMC is seeking air-burst capability for its 40mm UGLs and MGLs: see http://www.military.com/news/article...st-weapon.html

During the last few years Germany, Israel, Singapore and South Africa have each been rumoured to be developing FCS-fuzesetters or sights with dial-in fuzesetters for air-burst 40x51mm MV and also for 40x46mm LV cartridge grenades. So candidate systems for USMC evaluation could include several of these.

[Compost]

Last para of item 72 is misleading. Copy of the recent USMC RFI for airburst 40mm cartridge grenades is available at
https://www.neco.navy.mil//synopsis_...13_Oct_11.docx

RFI specified proximity fuzed 40mm LV grenades to engage defilade targets between 30 and 150 metres. Ammunition to be compatible with M203 and M32 launchers without requiring any modification or addition of equipment. RFI closed on 5 Dec 2011 at 4PM.

[jcustis]

I submitted an idea to the Marine Enhancement Program a few years ago, recommending the exploration of an indirect fire sight to allow for the M203 to be employed in an IDF mode, similar to the the sling technique that has been all but forgotten.

The MEP folks said it would be pushed past Gunner Eby at that time to review, and it seems it didn't stick.