Many rifle grenade designs currently offered use “bullet trap” or “bullet through” features allowing them to be fired by standard ball rounds. Grenades that need to be launched by a blank or ballistite cartridge may still be encountered, particularly for riot munitions where live rounds traveling down range is undesirable.
When using a ballistite fired grenade many modern rifles require the gas port of the barrel to be closed before firing which necessitates that the bolt be manually operated. This is mainly a requirement for weapons with a gas regulator that vents to atmosphere, such as the FAL. If the regulator is not closed or isolated the greater inertia of the grenade causes most of the propellant gas to be vented. Some weapons have a closed position on the regulator where others offer more foolproof and convenient designs. The Italian AR70s, for example, have a lever that lies along the top of the barrel and prevents a grenade being fitted unless it is raised. Raising the lever shuts the gas port and also obstructs the rifles normal sights, reminding the shooter to lower the lever when he has finished launching grenades. As far as I'm aware the firing of bullet trap or bullet through grenades would not need the operation of the gas cut off but this may not be true for all rifle/grenade combinations. Rifles with a closed gas system or that do not use gas operation do not require a gas cut-off when using ballistite launched grenades. These include the AK-series, M16, M14, Garand HK G3 and HK33 and bolt-action rifles. As an interesting side note during the 1950s the German Army issued a requirement for an SMG that could launch anti-tank grenades. At least one prototype included a bolt-locking device so the full force of the ballistite 9mm cartridge was used to propel the grenade. Just like a mechanism with a gas cut-off the bolt would then need to be manually operated.
Combined Rifle/Hand Grenades.
The idea for a combined Rifle/Hand Grenade was proposed by Mike Sparks. On this page I expand on the idea and suggest some of the features that such a grenade might have.
In the hand thrown mode it should have a conventional appearing safety lever and pin arrangement.
For muzzle launching the fuse would be activated by the acceleration of launching or by the bullet impacting the bullet trap.
Some mechanism will be needed to prevent the pin and lever mechanism being used if the grenade is fixed to the muzzle.
I think that the most practical approach to produce a Rifle/Hand grenade is not to adapt a Hand grenade to rifle launch but to adapt a rifle grenade design to hand throwing. A weapon like the FN Herstal Bullet-Thru® Telgren is similar in size to a hand grenade in its un-telescoped state (40 x 190mm). All that is really needed is a pin, safety lever and new fusing mechanism. Since the fuse will need to be changed a multi-option model can be fitted, as will be described later.
I feel a good basis for the Rifle/Hand Grenade would be FN Herstal Bullet-Thru® Rifle Grenade, which used to be called the Telgren. This has a pull-out tail section that contains the firing pin. When in the traveling configuration with the tail retracted the firing pin is not in line with the detonator in the grenade head. To fire the grenade the tail section must be pulled out and the grenade placed over the rifle muzzle. The grenade is a bullet-through design so there is no need to load a blank/ballistite cartridge since it can be launched by ball, AP or tracer rounds. When fired a spring retracts the tail of the grenade back into the body but also rotates it so the firing pin is brought into alignment with the detonator. Arming distance is between 5 and 10m. Launch velocity is 85m/s with a 7.62x51mm weapon, 65m/s with a 5.56x45mm. Range is 400m with a 7.62x51mm and 300m with 5.56mm. Each grenade weighs 320gm (11¼oz). Recoil for a 5.56mm is < 45J and < 60J for 7.62mm.
A rifle/hand grenade would be very similar but have an electronic fuse and a separate firing system for hand throwing. Electronic grenade fusing systems have been in use for some time, one of the best know companies using these being the British company HALLEY & WELLER.
This hand-throwing fuse system would operate by the familiar safety-lever and pin system, although the lever will be a non-ejecting trigger bar rather than a fly-off lever. This trigger bar or the tail might also mount a folding ladder sight that can be used when the grenade is muzzle launched. The hand-throwing system will only work when the tail is contracted into the grenade head. When the tail is pulled out for rifle-launch the hand-throwing fuse will be physically separated from the detonation circuit in the grenade head. If the safety pin is pulled while the tail is extended there will be no effect other than the safety bar partially releasing. The grenade will arm when rifle-fired regardless of whether the safety pin is in place or not. If the grenade was readied for rifle-firing but was not used the tail can be collapsed back into the head to return it to hand-throwing/traveling configuration. If the pin was pulled while the tail was out then retracting the tail will not reactivate the hand-throwing fuse system. To rearm the hand-throwing system the safety lever must be fully depressed and a safety pin reinserted. Alternately, if the safety lever has been released it will physically block the tail being fully contracted back into the grenade body. The ignition systen for hand-throwing will only work if it is in contact with the detonation circuit in the head, which only occurs if the tail is fully contracted. The tail cannot be fully contracted unless the safety lever is pinned down.
On the right is a crude representation of what a Rifle Hand grenade might look like.
A shows the weapon ready for hand throwing. The Soldier just pulls the pin and keeps the green safety bar depressed until he is ready. He may replace the pin to make the weapon safe again. The safety bar has a clip that prevents the ring rattling. In the illustration the ring has been detached from this clip and hands down the side.
In B the tail has been pulled out ready to be placed on the muzzle of the rifle. The pin does not need to be removed since extending the tail has disconnected the hand thrown firing system and the grenade will be armed by the action of firing.
In C the pin has been accidentally removed while the tail was extended. Pulling the tail out disconnects the hand thrown firing mechanism. The hand thrown firing mechanism will only work when the tail is fully retracted. Releasing the safety lever when the tail is out allows the red safety pin to extend, locking the tail in the open position. The tail can only be fully retracted if it can push the red pin down and the red pin will be locked in the extended position unless the safety lever is compressed. Therefore the tail can only be fully retracted and the hand firing system armed if the safety lever is compressed.
An electronic grenade fuse is not only more reliable and consistent, it can also have several fusing options. These may include: -
Long delay (for rifle launched use)
Impact with short delay
Impact with long delay (self-destruct mode). This setting can be used for when dropping from tall buildings, cliff tops, helicopters etc.
Impact with ½ second delay and self-destruct. Allows the grenade to be bounced off walls to engage targets around corners or bounced from the ground for an airburst effect.
Booby-trap. Grenade explodes when the pin is removed UNLESS the safety lever is being held - in this case the fuse defaults to short delay. Booby trap mode would be deactivated when the grenade is being rifle-fired.
For ease of use these options can be selected using just two tumbler or slider-type controls:- one to select or switch off the Impact mode, the other to set the Time/Self Destruct delay option. The Impact dial would have the options Impact, Impact + ½ and Off. The time dial has options such as 4 sec, 7 sec and Instant (0). Booby trap setting would be the controls set to Off, 0, easily remembered due to the two Os in Booby.
As well as the general purpose fragmentation Rifle/Hand grenade there are likely to be several other types. A Smoke/Incendiary Rifle/Hand Grenade containing White or Red Phosphorous would be very useful. There may also be requirements for a non-incendiary screening smoke grenade containing something like HC composition. Another potentially useful Rifle/Hand Grenade would be a Flash-Bang/Stun grenade that can be either hand thrown or rifle projected. In the latter mode it would be useful in deterring mobs. Another consideration is that the Rifle/Hand grenade should also be compatible with 7.62x51mm rifles and 9mm and .45 submachine guns.
A practice version of the grenade in rifle-launched configuration should be built that can be launched by blank rounds but has the same trajectory as the live grenade propelled by a ball round. Training could be an up-dated version of the medieval game of Rover:- essentially Golf using a longbow. The Soldier would move over a course of rural and urban terrain with targets at varying ranges and elevations, and be required to hit each with a practice grenade.
Rifle-Hand Grenades would also be used in the High Angle Grenade Launcher and could be adapted for launching from Recoilless Grenade Launchers or 3BT Grenade launcher. For launch from the MBIL/RLGL the grenade is fitted with a rocket that has a post that inserts into the grenade's extended tail. For the 3BT the Grenade is attached by a sear pin to a post on a cartridge case. Once sufficient chamber pressure is reached the pin breaks and the grenade is launched.
Another form of Rifle grenade that should see wider use is the Israeli IMI ARG/AP-50. This is a form of rifle grenade that does not leave the muzzle but instead projects a cloud of flechettes. These have proved very useful for firing through chain-link fences erected to protect from RPGs. The 53mm calibre round weighs 640gms and fires 160 flechettes in a 10° arc with a range of 50m. Such a weapon would be useful for any situation where the enemy was likely to be encountered at close range. Carlton Meyer coined the phrase Rifle-Claymore for a weapon of this type.
Other ideas about grenades can be found on these pages:-