It is not one of my habits to post in a public forum, but I will answer your question as best as I can, Suicide_Commando. Firstly, I posted the official Department of Defence concerning the Special Purpose Receiver used by United-States Army SOCOM :
Special Purpose Receiver (SPR) for the M16/M4-series rifles and carbinesNotice Date : 4/1/2002
Description : This announcement is for the re-initiation of an earlier project that was delayed due to urgent support of current hostilities. This announcement constitutes a Commercial Agency Announcement (CAA) and a synopsis of an upcoming solicitation. This CAA cancels and replaces SOL N00164-01-R-0103. This CAA is advisory only, alerting industry to the government's plans to publish a Request for Commercial Offerings (RCO) solicitation, and summarizing the future RCO for industry information.
The Navy is issuing this CAA on behalf of the U.S. Special Operations Command (USSOCOM) Special Operation Peculiar Modification (SOPMOD) Program and other federal agencies. A solicitation will be published on or about 19 April 2002 that seeks to award IDIQ contracts to vendor(s) who can provide accessory parts and assemblies for performance improvements to the M16/M4-series rifles/carbines.
Specifically required are Special Purpose Receivers (SPRs) for both short and long range precision fire, with improved MILSPEC 1913 rail interfaces, as well as related improved weapons parts and assemblies. These improvements may be Non-Developmental Items (NDI), Commercial Off-The-Shelf (COTS), or NDI/COTs that can be rapidly developed into suitable items for U.S. Special Operations and Law Enforcement.
Background : Special Operations Forces (SOF) operates around the world in extreme conditions including underwater, surf-zone, desert, arctic, jungle, and urban environments. They subject their weapons and equipment to extremely high usage rates and stresses. Due to the manner in which SOF utilizes its equipment, normal military specifications are in many cases not stringent enough to support SOF use. Although the currently fielded M16-series Rifles and M4A1 Carbines meet military performance specifications, these weapons have exhibited performance characteristics that do not meet SOF requirements when subjected to the extreme operational conditions imposed upon them by SOF operators.
General, Objective 1 (SPR Rail Interface) : Sources are sought for new SOPMOD rail interface designs. The SOPMOD program is not seeking alternate sources for the currently fielded SOPMOD Rail Interface System (RIS, NSN 1005-01-416-1089), rather is seeking alternative Forearm rail subsystems with improved operational performance characteristics :
(A) Rail Positions : As with the current SOPMOD RIS, MILSPEC 1913 rails are still required in the 12:00, 3:00, 6:00, and 9:00 positions on the rifle/carbine forearm. As an objective, the SPR 12:00 rail will be continuous and unbroken from the rear of the upper receiver to the forward gas assembly to permit rigid mechanical alignment of eye-axis aiming accessories.
(B) Forward Compatibility With Future EGLM : A rigid or monolithic interface method is desired that will allow a future EGLM to be mounted in the 6:00 position, while
(1) Withstanding the shock of firing all currently fielded 40mm Low Velocity rounds,
(2) Maintaining zero repeatability of the EGLM when removed and remounted,
(3) Allow the EGLM to be mounted as closely to the rifle/carbine barrel as possible without interfering with host weapon barrel harmonics during firing.
General, Objective 2 (SPR Performance) : To ensure system balance, also sought are rifle/carbine parts, components, subassemblies, or modifications that enhance reliability, endurance, safety, and operational performance as compared to the current M16/M4 series rifles/carbines. The Government is not seeking alternative sources of current parts for the current M16-series/M4A1 carbines, rather is seeking alternative parts and subassemblies that significantly increase weapon reliability and performance.
(A) Parts And Subassemblies :
These improvements, listed in priority order of government interest, may include new and improved
(1) Magazines,
(2) Bolt assemblies/bolt carrier groups,
(3) Barrels,
(4) Upper receivers and upper receiver groups,
(5) Trigger, sear, and hammer sets, (6) ambidextrous weapon controls,
(7) Flip-up/spring-up front and rear iron sights,
(
Front and rear pistol grips,
(9) Buttstocks, and
(10) Bipods any other components of, or mechanical accessories to, the M16-series/M4A1 carbines, with the exception of the lower receiver.
The government wishes to avoid modifications to the lower receiver.
(B) Versions : The SPR, should be optimized for
(1) Precision fire operations, and
(2) A capability to adapt weapon to mission needs with barrel lengths appropriate to the operational mode.
The barrel lengths are nominally 9 to 11.5 inches for close quarters battle and 16 to 18 inches for precision fire. All versions must fit M16/M4 series lower receivers. Parts commonality between the two versions is a secondary goal.
(C) Other Performance Goals :
(1) Increased reliability, durability, corrosion resistance, ease of cleaning, lubricity/reduced friction; fully functional for a minimum of 15,000 rounds (Threshold)/30,000 rounds (Objective), performing up to the standards and firing rates to be published in the Solicitation, functional reliability exceeding that of the standard M4A1 carbine at high and low temperature extremes as well as other hostile (sand/dust/dirt/mud/surf) environmental conditions
(2) Improved safety- delay cook-off, fail-safe features, fires/functions safely and without delay of draining in the Over-The-Beach (surf zone, weapon flooded with water) environment.
(3) User Acceptance: operational suitability, increased live-fire hit scores, decreased live-fire engagement times, speed/accuracy of engagement, controllability in semi-automatic and full automatic fire, improved handling qualities, light weight, snag free in movement through vegetation and battlefield obstacles.
Now concerning the magazine question, the answer is quite simple. Currently, the civilian clone of the SPR, which is now quite popular, use regular twenty-rounds magazines and pre-ban thirty-rounds magazines. Yet, the military version, can use the issued thirty-rounds magazines and the now rare twenty-rounds magazines. Hope that is what you wanted to know...
