An earlier form of this article appeared as part of a larger article in G2mil. Readers are refered to that site for alternate views on the subject.
Anti-Material Rifles and Related Weapons.
Anti-Material rifles (AMRs) and large calibre sniping rifles seem to both have gained popularity with the military community at the same time. Although the two weapons appear similar, the main design consideration of a sniping weapon is range and accuracy, while AMRs are designed for damage and penetration. The two roles do overlap somewhat. In the Gulf .50 calibre sniping rifles were used to damage artillery guns.
One of the first designs to be offered was the Steyr AMR. This fired a saboted fin-stabilized dart of 310gr at 1450m/s that could penetrate 40 mm of RHA plate with considerable secondary fragmentation behind the plate. Although it opened many people's eyes to the potential of AMRs the Steyr has been essentially overtaken by designs using more readily available rounds.
AMRs have been proposed for various roles. They have been suggested as a weapon to be used against APCs, though it could be argued that during an attack these vehicles will be positioned in overwatch way behind the attacking tanks and infantry. The AMR will need to have sufficient range to attack vehicles deployed in this way. It is not unlikely that future Anti-armour platoons will have an AMR squad which can engage lighter AFVs and free the ATGW crews to deal with the Main Battle Tanks. It has also been suggested that such weapons can be used against helicopters or to "peel" reactive armour from tanks to make them more vulnerable to other weapons. In Croatia AMRs were a vital element of night operations since they were needed to destroy tank-mounted armoured Thermal Imagers. AMRs could also be used to "snipe" at exposed tank commanders, easily defeating any body armour they are likely to have. Another interesting suggestion is that large calibre AMRs be used for remote explosive ordinance disposal. Special disrupter rounds filled with water, aerogel or foam could be developed for this role. One of the most interesting suggestions for AMRs was as that of a Special Forces weapon to attack parked aircraft and other soft targets from a distance. Such Special Forces applications may require HE-I rounds rather than AP.
The most interesting AMR that I have seen is the South African NTW20 design. This weapon can be broken into two man-loads and offers the user the choice of 14.5x114mm, .50 Browning or 20x83.5mm MG151 ammo. It can also be moved as an assembled weapon for "shoot and scoot" operations.
An idea that occurs to me is to fit a 20x83.5mm case with a 10-15mm saboted round shaped for optimum aerodynamic flight. Such a round could be used for both sniping against personnel and to attack aircraft and light vehicles at long range. I've found no information on sabotted ammo for 20mm weapons, but there is no technical reason why these could not be produced since saboted rounds already exist for both .50 MGs and 25mm cannon. The performance of the Steyr AMR's round gives us some idea of how potent such a round would be and it would greatly increase the versitility of the 20mm NTW20 without the need to change barrels.
AMRs that offer a large calibre option are probably more useful since they offer more potential, both for target effect and possible ammunition types.
A SWAT team could use a CS containing round to punch through a domestic wall and deliver the payload to the room beyond.
A long range guided round is also more likely than in smaller calibres.
A 20mm weapon could also use a high velocity saboted round designed for optimal aerodynamic ballistic performance.
My main suggested innovation to the AMR is to reduce the felt recoil, allowing a lighter weapon to be used. My suggestion is to use a similar system to the Browning recoilless shotgun. The barrel and breech are on a rail and when the trigger is pulled the barrel and breech is pushed forward down the rail, so the bullet leaves the muzzle as the barrel is still moving forward and this momentum must be overcome before recoil is felt. This system is said to reduce recoil by 72%, and the rearward motion of the mechanism could be further dampened by a buffer and muzzle brake. The rail mechanism may be mounted on a cradle that rests on the shoulder like a RPG. This would allow the weapon to be fired from a standing position against airborne targets if necessary. This system may not be sufficiently accurate for long range anti-personnel use weapon, but may be workable in an anti-vehicular role.
OCSW based AMRs.
When reading up on these weapons I came across a selective fire Czech design, the LCZ B-30 (Jane's Infantry Weapons 1998-99). This weapon weighed about 29lbs (13.2kg) and could be chambered for .50 Browning, 12.7mm Russian or 14.5mm and other rounds such as 15mm Mauser. Cyclic rate was given as 700rpm and a 16rd magazine was fitted. Interestingly by just changing the barrel and magazine this weapon is converted to an automatic grenade launcher. This launcher, the B-40 doesn't use low velocity 40mm grenades such as the 40x46mm. It uses the same 30mm grenade as the AGS 17, giving it a range of 750-990m.
Possibly an OCSW can be reconfigured to fire a high velocity smaller calibre round, either using saboted ammo or a replacement barrel, or a combination of the two. If the basic OCSW can fire a 132gm grenade at 425m/s then the system should be capable of firing a bullet equivalent in performance to a 50 calibre round or possibly the 14.5 or 15.5mm. Being able to fire a round like the 20x83.5mm MG151 would be highly desirable since the OCSW weighs less than the NTW20.
The OCSW could be made interchangeable between the two ammo types or it may be necessary to produce a dedicated weapon with most of the parts shared with the OCSW. The weapon could be expected to breakdown into two assemblies of around 30lbs and the weapon could be precision fired from its tripod to at least 2000m. Such a weapon would have a lot to recommend it to SOF forces.
It may also be possible to develop a heavy rifle using OCSW compatible ammo, or to build a lighter 20mm rifle using OCSW technology. Like the NTW 20 the weapon should be capable of being disassembled into two man-portable loads and equipped with a large carrying handle so that the weapon can be moved as a complete assembly. For certain targets a standard OCSW with AP(HEAT) ammo may have sufficient performance instead of an AMR.
Since I wrote the above passage a design of Payload Rifle using the same rounds as the OCSW (noe called the XM307 has been made public. This is based on a Barrett .50 Sniper rifle design.
Another "grenade firing rifle" is offered by the Philippino company of Floro International which offers a "High Velocity Grenade Launcher". Essentially this is a rifle that fires 40x53mm grenades. It appears to be a single shot semi-automatic weapon that uses recoil forces to open the breech and eject the spent case, rather like the mechanism of the Russian PTRD-41 anti-tank rifle. According to Jane's Infantry Weapons 2004-5 there are two models. The M2 is intended for firing from a bipod and weighs 10kg, while the M1 is for tripod or vehicle mounting and weighs 16kg. The M3 tripod designed for the Browning HMG can be used. The canister round contains 200 balls of steel shot and has a range of 45m.
AMR launched Rifle Grenades?
A option that has not been investigated with AMRs is their potential as grenade throwers. When the WW2 German PZB 38/39 anti-tank rifle became obsolete many were fitted with cup dischargers so they could launch grenades, including the various hollow charge models in service. A hollow charge grenade that could be launched from the Browning Heavy Machine gun was also suggested prior to the development of the Bazooka. German 37mm and 50mm Anti-tank guns also made use of muzzle launched Hollow-charge grenades. To the best of my knowledge, spigot tailed rifle grenades have not been built for AMRs, but the idea may have potential for both indirect and direct fire roles. Use of such grenades would give an AMR team an organic capability to illuminate distant targets during night actions.
Alternatives to Anti-Material Rifles.
There are other cheap solutions to light armour other than AMRs:-
One is to produce small high speed rockets for weapons like the RPG 2000.
A four barrelled launcher based on the 66mm M202 but loaded with HEAT rockets is another option, and this may have other applications such as being an alternative to SMAW.
Like the SMAW this launcher might use a spotting rifle. The spotting rifle would be a Sten gun like weapon in its simplicity and several rounds for this would be issued with each rocket reload. The original M202 was issued with Incendiary or Tear gas rockets. Various other projectiles may be possible, including anti-bunker rounds. The M72A3 rocket may form a good starting point for the HEAT rocket, while the HEDP equivalent could have a HESH warhead. Multiple rocket launchers made from Bazookas were used as trench artillery in Korea, so a similar weapon may still prove useful.
Another idea of an anti-light armour weapon is a repeating recoilless rifle of 25-40mm. A revolver mechanism would probably be simplest, and by diverting countershot gas from the barrel rather than the breech it may be feasible to use standard cannon shells as ammo.
This site on the Panzerfaust also has information on alternate German Anti-tank weapons, including Anti-tank rifles. Although it mentions them, it does not include much detail on the German Solothurm 20mm ATR or the 20/28mm Taper Bore "Heavy Anti-tank Rifle".