Abraham Flatau came up with the idea of Ring Airfoil Grenades (RAG) during the Vietnam war. The ring airfoil principle is simple to understand. Take a length of material with an aerodynamic cross section like an aircraft wing. Bend this into a ring and launch through the air with a little spin to stabilize it. Air passing thought the centre of the ring will be at a lower pressure than that passing over the outside of the ring and this generates lift. The lumen of the ring also gives the round less drag than a conventional round of similar calibre. Both of these factors mean the ring airfoil flies flatter and further. The term "Ring Airfoil Grenade" (RAG) can be found applied to two types of projectile. One is an explosive round that was tested in Vietnam, the other is a LLW (less lethal weapon) of similar application to baton rounds. Since it is non-explosive the latter round is sometimes termed a "Ring Airfoil Projectile" (RAP) Two forms of explosive RAG were tried:-
RAG-A had a 181gm round with a 142gm projectile, which was launched at 76m/s at a spin rate of 6000rpm to a range of 1000m. Calibre was 63.5mm and projectile length 35.5mm. Casualty radius was 1.4 times greater than the M406 40x46mm grenade, which would translate as a 7m radius.
RAG-B had a 113-160gm round with a 90gm projectile launched at 91-137m/s at a spin rate of 10,000-12,000rpm to a range of more than 1,400m. Flight time to 400m was 3.2sec and to 1,000m 9.2sec. Calibre was 54mm and projectile length 29.2mm. Idea of the RAG-B seems to be to produce a round with the same blast effects as the M406 40x46mm, so effect radius was 5m. The diagram on the right is taken from Jane's Infantry Weapons 1976 and represents RAG-B. Dimensions are slightly different to those published in later editions. The RAG-B was intended to create an infantry weapon that had a lethal area equal to existing systems while reducing bulk, weight and reaction time. The RAG-B flew faster and had a flatter trajectory than the 40x46mm, greatly increasing the probability of placing the round near the target. The RAG-B could be aimed and fired much like a normal rifle. Weight of the RAG-B grenade was much lighter than the 40x46mm (226gm).
Both the RAG-A and RAG-B were fired from shoulder fired weapons and a three shot weapon for the RAG-B was considered. here were also proposals for a Mk-19 type weapon that could be used on vehicles and helicopters armament. This article by Flatau suggests that fusing technology in the 70's was not sufficiently advanced.
Ring Airfoil rounds had been proven to be a viable idea and an application as seen for them in riot control. See here for the M234 Launcher
I'll take the liberty of quoting from one of these pages:-
"......rubber ring weighing about 1 ounce and banded with a special paper wrapping designed to hold the shape until impact. It was fired by a launcher-adapter that fit over the barrel of an M-16A1 rifle and propelled by a 5.56mm low-grain blank cartridge. The RAP flew at 200 feet per second, spun at 5,000 revolutions per minute, and delivered about 39 foot-pounds of energy. Flatau created two versions: the sting RAP and the soft RAP. The sting RAP was of particular interest to military police, who requested that it be accurate enough to hit a man-sized target from 40 to 50 meters, just outside of rock-throwing range, and a group of three people from 60 meters. Because one sting RAP could be used repeatedly, simply by rebanding it, it looked like a financially feasible tool, whether it was used for crowd control, in hostage situations, or as a training device. The sting RAP has the potential to stop a person, cause him to drop a weapon, or deter him temporarily to buy time for officers to respond to the situation. Biophysics testing showed the RAP could not break bones or injure internal organs, no matter how it was fired. It could, however, break double-pane glass, which was an advantage if one had to hit a subject inside a building. "You can fire it pointblank and it won't be lethal. It won't knock you down, and it's round [donut shaped, larger than an eye socket], so it can't poke your eye out. What it will do is get your attention, and on some people, it will leave a bruise." .....The second version, dubbed the soft RAP, offered a little extra punchit had 18 cavities embedded with tear gas that was released on impact, the development of a soft RAP embedded with oleoresin capsicum (OC) that will release a 3- to 4-foot cloud on impact "
The momentum of a 33gm (511gr) projectile at 200fps works out as 0.45 ftlbs/sec. This document explains how this velocity was selected:- "An extensive series of biophysics (wound ballistics) tests provided the launch parameters for the selected RAP size. Thus, for an approximately 2.5" diameter and chord of 1.35", with a flight weight of about 33 grams, the selected muzzle velocity was 200 ft/sec. The maximum velocity at which mixed results (serious injury) occurred was 215-220 ft/sec. Hence, by launching the RAP at a nominal muzzle velocity of 200 ft/sec, a safety margin of 15 to 20 ft/sec results. Another view of this is that if some additional impact energy is required, the launch velocity may be increased 15-20 ft/sec without making the RAP a lethal system."
Mention is also made of a new form of RAP launcher:- "The use of a launcher adapter on the M16A1 rifle is a somewhat inefficient means to propel the RAP. By comparison, the new launcher design is a more compact unit. It is essentially a self-contained device. That is, the shorter barrel contains a pre-loaded saboted RAP and a primer to ignite the propellant. Once the barrel is placed in the pistol frame containing the trigger mechanism, the device is ready to be fired. After firing, the barrel can be ejected and a "fresh" barrel can be inserted in the frame. It appears feasible to design and develop a multi-shot design that can firethree (3) successive RAP's and then be quickly reloaded."
The principles of ring airfoils have also been applied to pistol ammunition. Using this it is possible to have a round with high density and high velocity while still having a full calibre and good ballistics. Keeping the round full calibre improves its effects against both unarmoured targets and armoured targets who's protection is penetrated. Good ballistics extend the range at which the round retains an effective performance. The "Law Grabber" hollowpoints in the 1997 Shomer-tec catalog have a "toothed tip which acts as a flying hole saw, rotating at about 45,000rpm...". A similar feature could be used on tubular airfoil rounds. A nice article on Flatau's pistol ammo is here:-
".........Flatau's true armor piercing design was developed by various government agencies. The ramp gouging problem was solved by extending the plastic pusher sabot through the ring as a nose. Reportedly, the 9mm version now referred to as the Cyclone can penetrate 72 layers of Kevlar! Some sources suggest that the ATF used the Cyclone round at Waco resulting in friendly fire casualties."
D.E. Watters College of Criminal Justice University of South Carolina