SEAL Recon Rifle

The SEAL Recon Rifle, built in-house by U.S. Navy SEAL Team armorers, and later by the Naval Surface Warfare Center, Crane Division (often referred to as NSWC-Crane or "Crane"), was developed to provide SEAL snipers with a portable, lightweight, accurate weapon with greater lethality than a standard M4 carbine. The SEAL Recon Rifle is sometimes referred to as the "Recce Rifle".
When production of this rifle was turned over to NSWC-Crane, U.S. Army funding and concepts were apparently incorporated into the program (there is some confusion as to the exact events). The SEAL Teams were apparently disappointed with the performance of the resulting Mk 12 Special Purpose Rifle (SPR), and convinced the program managers at Crane to return to the original specifications. Production of Recon rifle on the original pattern is progressing now according to several sources.
The Recce rifle's existence was more so a conceptualization of an accurized rifle that shares the same ammo as the standard infantrymen's rifle, with enhanced capabilities, than it is a specification in itself. However, as rifle technologies advanced throughout the 21st Century, the specifications begin to blend or blur tremendously.
Specifications.
The SEAL Recon Rifle was initially built in-house with the only specifications being the ability to shoot any 5.56×45mm cartridge in inventory (at the time this included the first iterations of the 77-grain (5 g) Mk 262 Mod 0 cartridge), and that the rifle have a barrel 16 inches (406 mm) in length.
The barrel blanks have a 1:8 in (203 mm) twist and are stainless steel with a unique heavy barrel profile, starting with 0.980 in (25 mm) in diameter for the first 2.60 in (66 mm) of length, then narrowing down to 0.850 (22 mm) in diameter, 0.750 in (19 mm) in diameter underneath the front sight block, and 0.725 in (18 mm) in diameter to the muzzle. The barrels have the Ops Inc 12th model suppressors with the specified muzzle brake to mount the suppressor. A carbine-length gas system is used. These barrels were mated to flat top upper receivers, and back up iron sights (BUIS) from KAC (Knight's Armament Company).
Beyond this, exact specifications vary. Since they were built in house, they seem to have been accessorized to personal preferences, with fixed (A1 and A2 styles) and retractable butt-stocks. (Original 4-point and improved 6-point Colt stocks, and the Crane/SOCOM/LMT stock are all in use.) Recon rifles built by Crane are reportedly all fitted with a free-float handguard system, the most popular being the Knight's Armament Co. M4 Match RAS and the LaRue free-float handguards in the longer lengths (which protect the barrel and provide more area to mount tactical accessories). Knights Armament Corp (KAC) free floated rails (P/N 20214) were most oftenly used by the time of Global War on Terror, which was the basis for the Mk. 12 mod. 1 rifle. Barrels were a mix of stainless Lilja or Douglas and SOCOM heavy profile barrels, the former offered exceptional accuracy (1 MOA or better) whilst the latter offer as much accuracy but with better barrel life. Some operators reportedly use various back-up iron sights (BUISs) by Knight's, ARMS Inc, and Troy Industries, while others do not. The range of optics used on Recon rifles is wide, with various models by Trijicon (like ACOG TA01, TA31F), Leupold (TS-30A1, TS-30A2), and Nightforce (NAVSPEC NXS 2.5-10x24) in use.