The grenade launcher section of GURPS High-Tech 4e p.142 primarily describes the “grenade gun”-type of launcher, such as the M203 or AGS-17. For other types of grenade launcher we need to look under “rifle grenades” on page 193. This makes the rather deceptive statement that “While this [a cup or spigot] is present, the gun cannot fire normally.”. The rifle could still fire bullets with a launcher in place. Most cup dischargers will block the use of the normal sights. A set of raised sights could have been fitted, but this was seldom done, the operator being expected to either remove the launcher or reserving the rifle for grenade firing only. A spigot launcher might only affect normal shooting if the grenade sights were raised. Certain rifles were operated normally with the launcher permanently affixed. I will cover spigot launchers and how they may affect shooting in another blog. Since High-Tech only mentions one type of cup discharger launcher I thought it might be interesting to look at these in greater detail.
I will use “grenade launcher” in the older English manner. In some languages the terms “shell” and “grenade” are effectively interchangeable. This use has creeped into English in recent years, as seen in the incorrect backronym “rocket-propelled grenade”. The Germans call some mortars “Granatenwerfer”. In Russian the term “grenade launcher” is taken to include many designs of rocket-launcher and recoilless weapon. The term cup discharger is also used for vehicle-mounted smoke-round throwers.
These weapons will be unfamiliar to many readers. Seldom are they seen in movies. Information on rifle grenades, and particularly cup discharger launchers is not commonly encountered. What information there is is often incomplete or unclear. I have had to make educated guesses in places. Many books on infantry weapons totally ignore the category. Yet more the 1.45 million of the Schiessbecher model alone were produced. Many designs served for several decades and similar devices are still used for riot control. Novelty devices that can launch golf balls or soda cans from rifles can be purchased. I believe a device similar to the former was used for assassinations in an episode of the (Steed and Peel) The Avengers.
All ranges are approximate. Effective range depends on many factors, including weapon accuracy, target size, effect area and target speed. A weapon with a small effect area needs to be got closer to the target than one with a larger area. All rifle grenades (not just those from dischargers) are low-velocity projectiles and are very subject to the vagaries of the wind. A head wind may significantly decrease range, a tail wind increase it. Cross winds will cause drift. The long fuse durations used with rifle grenades will give an idea of typical times of flight to a target. The long time of flight was also detrimental when engaging moving targets, such as when using anti-tank grenades
The cup discharger dates back to at least 1743. Cups that could be mounted on the muzzle of a flintlock musket, utilizing the the lug for the socket bayonet, are known. These gave the musket a similar capability to earlier “hand mortars” that were designed to project grenades.
Che Guevara described how a single-barrelled 16 gauge shotgun could be modified into a mortar-like weapon using a pair of rods or sticks for long bipod legs, and an assembly like a cup discharger. Similar weapons have been used in the Middle East. Such weapons can launch grenades, Molotov cocktails or pipe bombs to at least 100 yd and are easily constructed.
In modern times, cup dischargers are most commonly seen launching riot control munitions. One of the advantages of cup dischargers in this role is they can launch unmodified hand grenades. Typically the launchers are of around 66mm/2.5" calibre. The body diameter of the grenade used may be slightly less since the discharger must often accommodate the safety lever to. Cup-dischargers for riot munitions are produced for modern, 5.56mm and 7.62mm automatic rifles. Many police forces mount them on obsolete (often bolt-action) rifles, often with shortened barrels. Dischargers for 12 gauge shotguns, flare guns, .38 revolvers and 37-38mm riot guns also exist. The revolver mounted Smith & Wesson models launch a 38mm munition.
The Israeli company of ISPRA produces a notable model which has two different diameter cylindrical sections. One part can take spherical grenades such as the 83mm rubber pellet grenade. The smaller part can take cylindrical grenades of around 64mm.
The Discharger, Grenade, Anti-Riot L1A1 is effectively a cup discharger without a rifle. It resembles a 66mm vehicle smoke grenade launcher fitted to a tubular stock and pistol grip. Weight: 5.94 lb, 110yd range. Grenades 1.21 lb. usingA pair of 1.5V U2/D batteries electrically ignite the grenade propellant . When firing a button behind the cup must be depressed by the off-hand, so the launcher can only be fired two-handed. The launcher is mainly used with CS irritant grenades but can also launch smoke-screening grenades. It was primarily used for riot control in areas such as Northern Ireland rather than as a battlefield system.
The heyday of cup discharger use was the First and Second World wars. During the latter half of the First World War it began to be realized that the rifle was no longer the last word in infantry weapons. Even today, some armies still try to resist this idea! The Great War sees a shift towards the light machine gun, hand grenade and grenade launcher becoming the primary firepower of a squad.
The VB cup launcher, aka Viven-Bessières or “Tromblon” was a French device used on the 8mm Lebel rifle from 1916 onwards. It weighed 3.3 lb and was 50mm calibre. The launcher itself is very simple, the novel element being the design of the projectile. Unusual for a cup-discharger, the explosive projectile was fired using a conventional ball round, rather than a blank. The explosive projectile had a channel down its centre for the passage of the bullet. The passage of the bullet down the channel tripped a lever which initiated the fuse so the grenade exploded 8 seconds later. Range was up to 208 yards. The projectile weighed 1 lb and does not seem to be capable of use as a hand-thrown grenade. Range was determined by varying the launch angle and no special sighting systems seem to have been used with the VB. Smoke and illumination projectiles were also issued, but were launched by a blank. Also in use was a container that could carry a written message. This released yellow smoke so that it could be more easily located, but in practice the smoke volume was very small and difficult to spot. One suspects that the projectiles often buried themselves in the abundant mud of the western front. The French considered the VB a company-level weapon so several might be fired together at the same target, particularly in static, trench operations When fired from trenches the rifles were often placed in special racks, some designs of which could be set to variable elevations. The VB continued in service after war, but like similar weapons, seems to have migrated into as squad-level weapon. A French Foreign Legion cavalry platoon had two machine gun sections and two scout sections, each of the latter having a VB. The French Army was still using it at the start of the Second World War. Some VBs saw action in remoter areas of the French Empire, such as the Philippines. The VB continued to be used as a riot grenade launching for several decades after this, at least up the the 1990s.
The American Expeditionary Force adopted the VB design for use with .30-06 M1917 Enfield and M1903 Springfield rifles in 1917. These launchers did not remain in US service for long after the war.
The use of a ball round required that the barrel and the channel in the grenade remain properly aligned. This required that the launcher and grenade be manufactured to an adequate level of precision and that the launcher not allowed to work loose when fitted. Firing a ball round at up to 45° in the air was a safety concern at practice ranges, since the bullet could land miles away, still at lethal velocity. A training round using a very light wooden bullet was developed.
While the French (and later Americans) selected the VB, the British chose to develop their own design, settling on the Burns Grenade Discharger, which was trialed in France in 1917. This later became more commonly know as the “EY”. This had a calibre of 2.5" (66mm). Originally designed for the .303 SMLE, adaptors and variants were created that allowed use with the .303 P14 (No.3 rifle) and .300 (.30-06) P17 (M1917 Enfield). Using blank cartridges, the basic launcher could be used with either calibre. The Burns/EY was intended to be always fired at 45° and range was varied by the degree that the gas port was opened or closed. (Automatic rifles with a “vent to atmosphere” gas system need to have their gas port closed when using rifle grenades, otherwise the inertia of the grenade forces most of the gas out the port and the grenade is moved only a few yards, if at all. Seeing the term “gas port” in connection with a bolt-action weapon may seem confusing!). The gas port for the EY is on the launcher itself and is a vent resembling a sliding shutter. A tightening knob prevents the shutter moving from the desired setting. One model of EY used a rotating ring with a number of holes instead. With the port full open (all the holes over the port) range is around 80 yards. Fully closed, range is around 200 yards. Range increases by approximately 30 yards for each quarter the shutter is closed by. Note that the EY was fired with the rifle “upside-down”, with the trigger guard upwards. This placed the heel of the stock in contact with the ground for better management of the recoil forces. When used in the First World War trenches a variety of stands were used with these grenade launchers, some of which could be varied for elevation, even though the gas port setting was supposed to control the range. No sight was provided for the Burns/ EY until the adoption of the no.68 grenade.
The usual fragmentation grenade for the EY was the no.36/36M Mills Bomb. A “gas-check” disc that screwed into the base plug was added to modify the grenade for EY launch. A 7 second fuse was commonly fitted instead of the 4 second. The grenade is inserted into the launcher and the pin removed. The wall of the barrel keeps the safety lever in position until the grenade is fired. Grenades modified for launcher use could still be used as hand grenades, the base disc having no effect on throwing. One of the reasons for the gas-check disc was that the Mills Bomb is around 60mm and the launcher was designed to also launch larger diameter cylindrical grenades such as the no.37 (WP) and no.80 (WP). Illumination rounds were also available.
A Mills bomb weighed around 1.7 lb, and launched at around 47 yd/s, so the recoil of firing the launcher was around three times that of firing a bullet. This was why the rifle was held so that the heel was in contact with the ground. If the ground was hard it was recommended that a sandbag be used. Users were cautioned to keep their hands away from any metal parts when firing. The harsh recoil would affect sight alignment so the EY was used on rifles that were only intended for grenade launching. Reinforcing bolts and wire wrap were used on certain parts to counter the woodwork cracking. One of the explanations for the name “EY” is that many of the rifles used were stamped EY, this being an armourer’s abbreviation for “Emergency Use only”, many guns tasked with grenade launching being non-longer suitable for general use.
In 1940, the no.68 shaped-charge anti-tank grenade was adopted for use with the EY. This role required the launcher to be fired at shallower trajectories (10°) so a dedicated sight was fitted. The end of the grenade projected past the muzzle of the launcher and the horns of the sight were aligned with the curve of the end of the grenade. A variant sight had a stepped cut-out, permitting it to be used with either the .303 SMLE and P14 or the .30-06 P17. The British Army had adopted the No.4 Lee Enfield but the EY seems to have been fitted on the by then obsolescent SMLEs. The Home Guard was using SMLEs, P14, P17s and Ross rifles. The no.68 grenade weighed 2 lb and low angle shooting required inventive ways to handle the increased recoil. It was recommended that the butt be placed on soft turf or a partially filled sandbag. It should never be used from the shoulder. If fired from the hip it was cautioned that no part of the rifle should be in contact with the body. Penetration was 52mm.
When the 2.5" launcher was being trialed in autumn 1917, experiments were conducted with a version designed for the No.34 “British Egg” grenade. The No.34 was a design that had been created by the British Army in France and was felt by some to have some advantages over the Mills, which had been invented on the British mainland. The two models had possibly complimentary roles. The No.34 weighed 0.65 lb and was 41mm in diameter. Weight for weight it produced 30% more fragments that the Mills. It could be hand-thrown to a greater distance, so the user was in less danger from fragments from his own grenade if the weapon was used in the open. Fired from its cup discharger, the No.34 had a range of 500 yd, compared to 200 for the No.36. The Mk IV version of the No.34 added a ring cast around its widest point that served as a gas check. A safety pin and a shear wire held the striker pellet used for igniter of the No.34. Some other grenades intended for discharger launch, including the No.37, used this igniter (“Adams striker mechanism”). Once the safety pin was removed, the acceleration of launch caused the striker pellet to break the wire and start the 7-second fuse burning. There was no danger that a grenade might be accidentally inserted with the safety lever outside the cup, since there was no safety level, the fuse being triggered by the violence of launch. For hand-throwing, the striker pellet was hit against a hard object such as a helmet or boot-sole. A fuse working the same way was used in many Japanese Second World War grenades. These too, activated automatically when launched from the Type 100 cup discharger or knee-mortar. Potentially, the No.34 Mk IV may have been the better discharger round. The lighter weight may have meant reduced recoil forces as well as longer range. The long narrow shape of the grenade may have given a shorter time of flight, contributing to accuracy by reducing the effects of wind on the grenade. The idea that a soldier might carry two different calibres of cup-discharger was rejected. Perhaps the larger version was selected since it could handle other models of grenades such as the No.37. With hindsight, a dual calibre design along the lines of the later ISPRA could have been tried. Or a sabot, as used on the later Yugoslavian RB-100 grenade. This, and other earlier Yugoslavian grenades, particularly the Mod.1917 grenade, bears a striking similarity to the No.34. Over-calibre rounds, such as used with the Schiessbecher might also have been tried.
Around 1925, the British Army adopted a 2" version of the cup discharger. Intention may have been to address issues such as recoil and eliminate complications such as gas-checks that the variety of grenade calibres necessitated. A range of 2-inch grenades intended for use with this launcher included the No.54 fragmentation (17oz) , No.55 WP-smoke and a variety of signals and illumination. The No.54 and No.55 use a “weighted tape”-type “Allways” fuse, of similar principle but apparently a different model to the No.247 used on the later No.69, No.70, No.73, No.77, No.79 and N0.82 Gammon grenades. The “Textbook of Small Arms 1928” gives the range of the No.54 as more than 300 yd. It also tells us this model can be attached and used without detaching the bayonet. A portless model that used angling for range was considered, but some form of vent was found necessary for engaging short-range targets.
In 1933, the 2.5" launcher was readopted. The Mills bomb had remained in service. The “Textbook of Small Arms 1928” describes the No.37 with no indication that it was at that time considered obsolete.
As I have already noted, information on cup dischargers is relatively hard to come by. I have found no information on if the EY could be easily mounted on the No.4 or No.5 Lee Enfields, nor if so, whether this required an adaptor to accommodate the differences in muzzle configuration. I have yet to encounter any information on scale of issue in British service. The grenade launcher was presumably a squad or platoon-level weapon, but I have no information on how common or what numbers they were used in.
The EY was in use at least as late as the Malaya Emergency. The photo below shows a shortened Lee Enfield with an EY. This one is Irish or British, but other armies and police forces created similar. This one is claimed to have been used in the 1960s, presumably for riot munitions. The red markings on the magazine may be a caution to use blank ammunition, a notification the weapon uses .303 rather than 7.62mm, or both. Interestingly, the rifle has an aperture rear-sight so is either a No.4 or No.5 rather than a SMLE. The recoil pad of a No.5, or a No.5 stock with a recoil pad, has been fitted.
(Above) A non-EY smoke grenade launcher of a type used on universal carriers. The rifle part is a cut-down SMLE
During the First World War the Germans copied the VB. Battalions had a squad of rifle grenadiers. Their Gew.Spr.gr 1917 grenade had a 5-8 second fuse, weighed 1.76 lb and had a range of 165 to 220 yd. As the war progressed the grenade launcher became a weapon of smaller units.
The Schiessbecher was adopted in 1942, one launcher being held per rifle squad. The Schiessbecher was used on the Mauser Kar 98k and also a number of other rifles including the StG44, G43 and FG42. PzB 39 anti-tank rifles were shortened, modified and fitted with a Schiessbecher to create Granatbüchse Modell 39 (GrB 39) Weight: 23.15 lb, single-shot. The anti-tank rifle used a 7.92/13mm round so the propellant cartridge for grenades was based on a 13mm case. This gave a longer range than the launcher mounted on other rifles. Light anti-tank grenade: 0.55 lb 250 yd range, heavy anti-tank grenade: 0.8 lb 120 yd). Like the anti-tank rifles it replaced, the Granatbüchse was issued at three per rifle company.
The Schiessbecher is described briefly in the rifle grenade section of High-Tech 4e. The Schiessbecher is notable for being rifled and only 30 mm calibre.
The diameter of most cup dischargers prevents the use of the standard rifle sights. It is possible the No.34 launcher and 2-inch launcher may have been exceptions. The Schiessbecher does appear to allow the normal use of the rifle while fitted. The sights of the StG 44 are raised well above. There are numerous photographs of Kar 98k mounting Schiessbecher being aimed at low trajectories, suggesting bullets rather than grenades are being aimed.
For firing grenades, a rotating sight incorporating a spirit level may be mounted on the left side of the weapon. Often the discharger is used without the sight. There is no gas vent, barrel angle being used to select range.
Either a blank round or a case mounting a wooden bullet fired the grenades. Each different grenade type used a particular propellant round. These were distinctively marked and packed with the appropriate grenade. The relatively light weight of the grenades produced less recoil than the EY. This was an advantage since the anti-tank and anti-personnel grenades might be used in a direct fire rather than high trajectory role.
The use of a shaped-charge favoured larger-calibre projectiles. Some anti-tank rounds resembled toadstools, having a 30mm stem that fitted in the launcher and a larger diameter head that remained outside. All Schiessbecher are spin-stabilized, which reduces the effectiveness of a hollow-charge.
• High explosive grenade: 30mm, impact or allways-fused. Some models self-destructed 11 seconds after firing if an impact failed to detonate them before. Some variants could be used as hand grenades. These employed an operation similar to the stick grenade: the base of the grenade was unscrewed, the cord pulled and a 4½ second fuse ignited. 0.56 lb, maximum range 265 yd. A long-range version propelled by a wooden bulleted cartridge claimed a range of up to to 711 yds. This model lacked the self-destruct feature.
• 30mm (light/Klein) anti-tank grenade: 0.55 lb, maximum accurate range 50-123 yd. 25-30mm penetration. Velocity approx 55 yd/s
• 40mm (large/Grosse) anti-tank grenade: 0.84 lb, maximum accurate range 100 yd. 40mm penetration.
• 46mm anti-tank grenade: 0.97 lb, 90mm penetration. range 110 yds, maximum 200 yds.
• 61mm anti-tank grenade: 1.19 lb 126mm penetration. extreme range 220 yd. The SS independently developed 46mm and 61mm anti-tank grenades.
• 39mm Smoke grenade. Titantetrachloride (FM), 1.39 lb. Had a grooved skirt which fitted over the outside of the Schiessbecher.
• 30mm Parachute Illumination 0.62 lb Ejects a parachute flare 8½ seconds after firing. Burns for 25 seconds, illuminating targets up to 765 yds away.
• 30mm Propaganda leaflet grenade. 0.5 lb (loaded with leaflets), ejects 0.125 lb of leaflets 9 seconds after firing. Maximum range is approximately 500 yards.
The Japanese used the Schiessbecher as the Type 2, and their own design, the Type 100 cup discharger.
The Type 2 fitted the 6.5mm Type 38 and 7.7mm Type 99 rifles. Ammunition was a 30mm and a 40mm hollow-charge anti-tank rounds. The 30mm weighed 0.5 lb and gave 30mm penetration of armour. Firing created little more recoil than firing a normal ball round and a 30mm grenade could be placed in a one yard square at 55 yards. A experienced user could hit a tank at 100 yards, the grenade taking two seconds to reach this distance. The 40mm grenade weighed 0.81 lb and gave 50mm penetration. The 40mm grenade produced more recoil and could not be shoulder fired. The 40mm was also found to be inferior to the 30mm, being less stable in flight. The Type 2 did not prove effective against American tanks in Burma.
World War Two sources claim there was a variant of the Type 100 for the 6.5mm Type 38 rifle and another for the 7.7mm Type 99. Other sources state the early Type 100 could only be used with the 6.5mm rifle, while later production examples were universal and could be fitted to either the 6.5mm or 7.7mm rifles. The bayonet must be fixed to secure the launcher in position. When in position the launcher prevents the use of the normal sights. Wikipedia claims the Type 100 used Type 91 (7-9 second fuse) and Type 99 (4-5 second) grenades. Some sources claim the Type 99 was the sole round for the Type 100. The Type 99 was 40-41mm in diameter, whilst the Type 91 and 97 were 50mm, so it seems more likely only the Type 99 was compatible. The safety pin of the Type 99 (or 91) is removed, and the grenade is placed in the cup, striker-pellet downwards. Grenades are fired with the rifle butt against the ground. The Type 100 used ball ammunition and diverted the propellant gases into a cup mounted on top of the barrel extension. The effective range is approximately 100 yards. Velocity was 82 yd/s from a 6.5mm rifle and 104 yd/s from a 7.7mm. Type 99 grenades exploded 4-5 seconds after launch.
Other Japanese Launchers
The Japanese also made use of simpler cup dischargers using blank ammunition, firing a type 91, 97 or 99 grenades base first. The pressure from the propellant gases compressed the striker and initiated the fuse. Such launchers were usually locally produced or improvised.
The Japanese “Knee-mortar” could also project modified Type 91 hand grenades and is sometimes designated “50mm Grenade Discharger”.
The Soviets used the Dyakonov grenade launcher. Designed in 1916, it was not adopted until 1928 and dropped from service in 1942, so was likely to have seen action in Soviet-Japanese Border conflicts, the Winter War and early Second World War. The Dyakonov appears to be a rifled VB-type weapon of 40.5-41mm calibre (probably 40.8mm, “16 lines” in older Russian measurements). A booster charge seems to have been incorporated in some projectiles. The Dyakonov was mounted on a standard M1891 Mosin-Nagant rifle, fitted in place of the socket bayonet. After the war some M44 and SKS carbines (which both had folding bayonets) were adapted to this launcher.
Recoil was harsh, so the weapon was fired from the prone position with the butt dug into the ground. Firing from a hard surface or frozen ground could be problematic. In 1939, each rifle squad was supposed to be hold a Dyankonov. A crew of two operated the Dyankonov, the loader carrying 16 grenades.
The launcher weighed 2.9 lb, the quadrant sight 1.5 lb and the bipod 4.9 lb. Rifle and all fittings weighed 18.1 lb.
• The anti-personnel round (0.83 lb) had a timed fuse that was set manually with a dial on the base before loading. Range was 330 yd, with up to 930 yd claimed if the booster charge was left in place on the base of the grenade. Casualty radius was about 33 yd, but fragments are claimed to travel up to 165 yd, potentially reaching the launcher team.
• Day signal. Adopted 1936, weight 0.3 lb. A blank round launched the signal to a range of 200-250 yd. After a 2½ second this burnt to release red, orange, yellow, blue or green smoke. The smoke burns for 20-40 seconds and may be visible for 60 to 90 seconds.
• Night signal grenade. Adopted 1936, weight 0.375 lb. Star of red, yellow, blue or green. A blank round launched to a range of 165-250 yds. Signal burns for 10-11 seconds. May be visible 10-12km away or as much as 25km under good conditions.
• Illumination grenade. Adopted 1936, weight 0.375 lb. A blank round launched to a range of 165-250 yds. Burns for 6-7 seconds, illuminating a radius of 110 yd.
The Dyakonov explosive round proved to be ineffective and unreliable. Despite the two-man crew, rate of fire was only 3-4 rounds per minute. Designed for the positional warfare of the Great War, the system was ill-suited to the often more mobile warfare of the era it was used in. The signal and illumination rounds had a useful performance but had durability and reliability issues.
The VKG-40 hollow-charge anti-tank grenade was fired from a modified Dyakonov launcher, adopted in 1944. Once modified, the launcher could not fire other types of Dyakonov grenades. The VKG-40 was a rodded grenade. Aa special blank round projected the anti-tank round to 165 yd. Armour penetration was 50mm and weight was 0.48 lb. The round was only suited to attacking very poorly armoured targets, and like other grenade launchers the long time of flight, high trajectory and wind effects made it difficult to engage moving vehicles.
Tromboncino M28 (“Little Trombone”) was an Italian grenade launcher of the interwar period, which was in service until 1934. While it does not seem to have seen any significant use, the design is interesting since it shows some features used in much later grenade launchers. It was mounted on the right side of the 17-inch barrelled 6.5mm Carcano M91TS carbine (6.4 lb), portending weapons like the M203. To use the launcher, the bolt had to be removed from the carbine and fitted to the launcher. The single trigger fired either the carbine or the launcher, depending on which the bolt was inserted in. The grenade launcher fired a 38.5mm impact-fused, cast-iron, finned grenade of only 0.36 lb to a range of 220 yd. A ball round projected the grenade, and is an early example of a bullet-trap mechanism. The launch mechanism also had features of a hi-lo pressure system later used in the M79 and M203.
23mm Launcher, 2018
In 2018, a video appeared from the Donetsk People’s Republic. The video demonstrated 23mm cup dischargers mounted on AK74s. Interestingly, the projectiles were HEI shells removed from 23x152Bmm cannon rounds, as used by the ZU-23-2 and ZSU-23-4. Other than the projectile choice, the device is a conventional smooth-bore cup-discharger using blank ammunition for propulsion. The high sights of the AK74 allow the device to be permanently attached.
Acceleration from the discharger is apparently sufficient to arm the fuse. Since the projectile is unstabilized, however, the chances of it arriving point first are slim. The system exploits the self-destruction feature of the fuse to detonate the shell after a period of time.
Timing for self-destruction varies:
• The MG25 fuse destructs in 14-19 seconds.
• The V19UK fuse destructs in 5.4–9.5 seconds.
• Jane’s Ammunition Handbook 2001-2002, states that South African-produced 23mm ammunition destructs in 5-12 seconds and that Yugoslavian rounds in 3.5 seconds.
In the video, one round explodes after 6 seconds and the other after 9 seconds. This suggests the V19UK fuse.
In game terms, detonation takes d6+4 seconds. An impact detonation only occurs on a critical success.