2014 STS Arms, LLC., all rights reserved.
ST4 Tactical:

STS Arms, LLC ST4 Tactical Rifle has the following specifications:

Barrel:  1x8 twist, 4150 steel, salt bath nitride (Melonite), 16 mid-length gas system advanced contour barrel, 14.5" with pinned comp on request, low pro gas block
Front Sight:  MBUS flip front
Muzzle device: Primary Weapons Systems FSC556 brake
Caliber: .223 Wylde or 5.56mm NATO
Bolt Carrier Group: M16 carrier, chrome lined, HP/MPI bolt, Microslick coated
Upper and lower receivers: 7075 forged aluminum, A4 flat top upper, mil-spec dimensions, Microslick coated interior
Trigger guard: Magpul MOE
Trigger: JARD adjustable or non-adjustable LE model
Rear sight: MBUS flip rear
Charging handle: BCM Mod 4 or Butthead Tactical ambi latch
Buffer: Enidine ARrestor, red Cerakote coated action spring
Grip: Magpul MOE plus
Stock: Magpul MOE
Hand guards: Midwest Industries 12" SS gen 2
Magazine: Lancer L15AWM with steel feed lips or Pmag
Notes:
STS Arms, LLC ST4 Tac rifles replace the standard M4 contour barrel with a mid-length gas system advanced contour barrel with a salt bath nitride finish.  This change boasts many improvements over the mil-spec configuration:

-- The first improvement is an extra two inches of gas tube slows down the normal violence of the mil-spec carbine action cycle.  It recoils softer and more reliably, as a result.

-- The second improvement is an improved sight radius.  Because the gas system is integral with the sight base and now two inches closer to the muzzle, it moves the front sight further from shooter's eye.  This helps aid in better sighting and more accurate shooting.

-- The third improvement is the contour.  The old M4 contour was designed to be backwards compatible with the M203 grenade launcher system.  As most civilians are not going to be using this item, there is no reason to have both the carbine gas system, nor the funny cuts in the barrel to accommodate the launcher mount.  Instead, STS chose a barrel with a thicker contour under the hand guards and a lighter one in front.  This results in a rigid barrel which remains lighter at the muzzle end (for shooter comfort) and resists flex during rapid fire strings better than the mil-spec M4 contour.

-- The fourth improvement is salt bath nitride treatment of the barrel.  More commonly known as Melonite, this treatment hardens the surface of the steel to a Rockwell hardness of RC70 to a thickness of about 0.005" (compared to chrome lining at 0.0003" - 0.0005").  This results in extreme corrosion resistance, wear resistance, and increased natural lubricity wihtout loss of accuracy.

-- The fifth improvement is the 1x8 twist air gauged match grade barrel.  1x8 twist stabilizes 50 grain to 77 grain projectiles whereas 1x9 and 1x7 both have limits in bullet weights at either end of this spectrum.  Salt bath nitriding will not affect the inherent accuracy of the match bore, wheras chrome lining is widely known to adversely affect accuracy.
Note:  Rifle shown with optional 14.5" barrel and permanent brake and in Flat Dark Earth and OD green accents, Lancer L15AWM magazine.
ST4 Mini-Tac:

STS Arms, LLC ST4 Mini-Tac Rifle has the following specifications:

Barrel:  1x8 twist, 4150 steel, salt bath nitride (Melonite), 16 mid-length gas system advanced contour barrel, 14.5" with pinned comp on request
Front Sight:  Yankee Hill Machine flip front sight gas block
Muzzle device: Primary Weapons Systems FSC556 brake
Caliber: .223 Wylde or 5.56mm NATO
Bolt Carrier Group: M16 carrier, chrome lined, HP/MPI bolt, Microslick coated
Upper and lower receivers: 7075 forged aluminum, A4 flat top upper, mil-spec dimensions, Microslick coated interior
Trigger guard: Magpul MOE
Trigger: JARD adjustable or non-adjust LE model
Rear sight: MBUS flip rear
Charging handle: BCM Mod 4 or Butthead Tactical ambi latch
Buffer: Enidine ARrestor, red Cerakote coated action spring
Grip: Magpul MOE plus
Stock: Magpul MOE
Hand guards: Midwest Industries 9" SS gen 2
Magazine: Lancer L15AWM with steel feed lips or PMag
Note:  Rifle shown with optional 14.5" barrel and permanent brake and in Flat Dark Earth and Foliage Green accents, Pmag.
ST4 Comp Tac:

STS Arms, LLC ST4 Competition Tactical Rifle has the following specifications:

Barrel:  1x8 twist, 4150 steel, salt bath nitride (Melonite), 16 mid-length gas system advanced contour barrel, 14.5" with pinned comp on request
Front Sight:  MBUS flip front sight
Muzzle device: Primary Weapons Systems FSC556 brake
Caliber: .223 Wylde or 5.56mm NATO
Bolt Carrier Group: M16 carrier, chrome lined, HP/MPI bolt, Microslick coated
Upper and lower receivers: 7075 forged aluminum, A4 flat top upper, mil-spec dimensions, Microslick coated interior
Trigger guard: Magpul MOE
Trigger: Jard Adjustable or non-adjust LE model
Rear sight: MBUS flip rear
Charging handle: BCM Mod 4 or Butthead Tactical ambi latch
Buffer: Enidine ARrestor, red Cerakote coated action spring
Grip: Magpul MOE plus
Stock: Magpul MOE
Hand guards: Midwest Industries 15" SS gen 2
Magazine: Lancer L15AWM with steel feed lips or PMag
Note:  Rifle shown with 16" barrel and in Tungsten Grey with black accents.
MSRP:  $2399
MSRP:  $2399
MSRP:  $2439