Colt AR-15A4 Mk12-Style SPR in 5.56 NATO – Centurion Arms Upper & BCG, Douglas 18 in Mk12 Barrel, KAC SR-15/16 FF RAS, Geissele SSA-E, Magpul PRS Lite
This custom SPR/Mk12-style rifle combines a Colt AR-15A4 lower with a Centurion Arms flat-top upper and a Douglas 18-inch Mk12-profile barrel. It is outfitted with a Knight's Armament SR-15/16 Free Floating RAS (PN 21318) with KAC rail panels, a Centurion Arms Mk12 brake with collar, and a Centurion Arms bolt carrier group. A Geissele SSA-E two-stage trigger, Magpul PRS Lite adjustable stock, Magpul MOE-K2+ grip, and Magpul B.A.D. Lever round out a purpose-built configuration. The rifle is in excellent condition.
Condition
Overall Condition: Excellent condition, showing only faint signs of any prior use or handling.
Specific Condition Notes: Function is excellent.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
What’s Included
- 1x 30-round USGI-pattern aluminum STANAG magazine (CAGE 33710 marking visible)
- Magpul PRS Lite adjustable stock (installed)
- Magpul MOE-K2+ grip (installed)
- Magpul B.A.D. Lever (installed on bolt catch)
- Knight's Armament SR-15/16 Free Floating Rail Adapter System, PN: 21318 (installed)
- Knight's Armament ribbed rail panels (installed)
- Mk12-pattern muzzle brake with collar (installed)
- Geissele two-stage trigger (installed)
This build starts with a Colt AR-15A4 lower receiver bearing Colt Defense rollmarks and mates it to a Centurion Arms flat-top upper with T-marked Picatinny rail, forward assist, and dust cover. The Centurion Arms bolt carrier group is installed for a matched upper assembly.
The barrel is a Douglas 18-inch Mk12-profile unit chambered in 5.56 NATO with a 1:7 twist and a low-profile gas block. At the muzzle, a Centurion Arms Mk12 brake is paired with an Ops Inc/Allen Engineering-type collar, completing the SPR-style setup.
Handguard and mounting are handled by a Knight's Armament SR-15/16 Free Floating RAS, PN 21318, with KAC ribbed rail panels. There are no iron sights or optics included.
Controls and ergonomics include a Geissele SSA-E two-stage trigger, Magpul PRS Lite adjustable stock, Magpul MOE-K2+ pistol grip, and a Magpul B.A.D. Lever on the bolt catch. The rifle operates via a semi-automatic, direct-impingement system with a manual safety selector and uses standard 30-round STANAG magazines.