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 " ) , the SEAL Recon Rifle was developed to provide SEAL sniper s with a portable , lightweight system 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 Rifles " on the original pattern is progressing now according to several sources . Specifications . According to Wes Grant of M . S . T . N . a premiere small arms builder , these weapons were initially built in - house with the only specifications being the ability to shoot any 5 . 56 x 45 mm 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 weapon have a barrel 16 inches ( 406 mm ) in length . 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 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 armament corp ) . 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 .