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 Rifles" on the original pattern is progressing now according to several sources.
The barrel blanks are made by Lilja Precision and then chambered by Compass Lake They have a 1:8 in (203 mm) twist and are stainless steel. They have 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 Knight's Armament Company - KAC QD (Quick Detach) flash hider, allowing the mounting of KAC's QD sound suppressor. A carbine-length gas system is used. These barrels were mated to flat top upper receivers, and retained the fixed front sight/gas block assembly, which would seem to imply that the original iterations were probably just rebarreled M4/A1 type carbines in SEAL inventory.
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). 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 in use.
Due to the secretive nature of the end-users, first-hand information and data regarding the Recon rifles seems to be quite rare. How much these specifications have changed with regards to Crane's "production" weapons is unknown.