The Beretta Rx4 Storm is an Italian semi-automatic rifle manufactured by Benelli Armi on behalf of Beretta. The original Rx4 Storm was designed by Beretta Holding (a division within Beretta) alongside the Px4 Storm (pistol) and Cx4 Storm (Carbine).
The Rx4 Storm was designed to use the patented Auto-Regulated Gas Operation system, developed and patented by Benelli Armi. This action, using the force of the gas to rotate a bolt to lock the barrel and load the next cartridge, is designed to be more efficent than conventional gas operating systems used in firearms, having been adopted in various other designs in use by various military forces already. The Rx4 Storm will only fire in semi-automatic mode.
The Rx4 Storm is available with the option of having a fixed or adjustable stock, while also being fitted with a top-located picatinny rail as standard. Furthermore the Rx4 Storm is fitted with nine seperate sling mounting points to allow for better carry control. The standard sight consists of a combat Ghost Ring, capable of adjustment to allow for windage and elevation.
The Rx4 Storm has it's gas port (where expended, high temperature gases are released after firing) located slightly forward from the chamber, the reason being that the gases are at their hottest at that point. Yet, despite being part of the same "Storm" line as the Px4 Storm and Cx4 Storm, the Rx4 Storm shares no operating or functional features with the former two.
The Rx4 Storm was originally developed/tested using a 6.8x43mm testing cartridge, originally based on the .223 Remington. This therefore meant that the Rx4 Storm, upon its release, would be available chambered to accept the 5.56 NATO, which was also developed from the .223 Remington (ie the .223 Remington is the parent case of the 5.56 NATO). Unsuprisingly, the Rx4 Storm can also fire the .223 Remington.
Either of the calibres can be fired from the STANAG Magazine, a typical design of magazine that many rifles are designed to use. The magazine capacities used for the Rx4 Storm include 10, 20 or 30 rounds, with the magazine itself clipped to the underside of the barrel/frame.
Within a few years of the Rx4 Storm's release in 2005 a relatively large number of variants had become available. The majority of these variants are simple changes of barrel length or stock types.
The most common specification change to the Rx4 Storm from the standard version is the use of a 315mm (12.5in) threaded barrel fitted with a detachable muzzle brake. This specification of the Rx4 Storm is fitted with a picatinny rail mounted to the top, with extensions added (but removable) to the side, bottom and fore-end of the Rx4 Storm.
The Beretta Rx4 Storm was developed alongside the Px4 Storm pistol and Cx4 Storm carbine, as part of the "Storm" range. Although models sold in the US are named Beretta Rx4 Storms, those sold in the rest of the world are marked/named Benelli MR1. The Rx4 Storm is manufactured in both Italy and the US by Beretta plants, alongside the Px4 Storm and Cx4 Storm, despite the fact they share no common parts.
Beretta had never intended for the Rx4 Storm to be used by the military (pursuing a newer generation of assault rifles instead) preferring instead to focus on selling the Rx4 Storm as home defence / "varmit" gun. The earlier mentioned changes commonly applied to the Rx4 Storm were designed to attract police/patrol forces into buying the Rx4 Storm, although no forces have yet decided to use it.