The MK4 is a precision oriented upper receiver. Accuracy and consistency is the main focus here. No frills, just the most precision you can squeeze out of 5.56 AR platform with out the price tag. I guarantee MOA 5-shot groups with high quality ammo. In my personal testing I have gotten right at 1 MOA 10-shot groups. These are not lightweight uppers as the barrels alone come in at just over 3lbs.
The Basics
18" SPR Ballistic Advantage 5.56 Barrel, 15" KAK Mlock Rail, AO TMS BCG, Mil-Spec Upper and Charging handle
The Specifics
Barrel:
Manufacturer - Ballistic Advantage SPR
Length/Chamber - 18" 5.56
Twist - 1:7 Twist
Material - 4150 Chrome Moly-Vanadium
Profile - SPR with OPS 12 Compatible Collar
Gas System - Rifle
Finish - Nitride
Thread Pitch - 1/2x28
Gas Port - Drilled to MK12 Spec .104"
Dimpling - Yes
Weight - 41oz
1st Rebarrel - FREE
Barrel nut is sequentially torqued down to 50 FT-lbs. Starting at 25, then 35, and then finally 50 FT-lbs. to ensure proper mating of the threads.
If you legit burn out a barrel, like 10,000 -25,000 rounds, and the barrel becomes inaccurate I will rebarrel it for you for free. Good luck.
Bolt Carrier Group:
Brand: AO Precision True Mil Spec BCG
Bolt Material - C158 Alloy
Carrier Material - 8620 Alloy
Gas Key Material - 4130 Alloy
Profile - Full Auto
Finish - Phosphate/Chrome
Gas Key Screws - Grade 8 (torqued and staked to Mil-Spec)
Forward Assist Cuts
Mil-Spec Firing Pin (Hard Chrome Coated)
*Individualy MPI/HPT tested
Handguard:
Manufacturer - KAK
Length - 15"
Material - 6061 T6 Aluminum
Finish - Hard Coat Black Anodization
Mounting Platform - 7-Sided Mlock
Barrel Nut - Steel (does not require timing)
Upper Receiver:
Manufacturer - Aero Precision/Anderson
Material - 7075 T6 Aluminum
Machined from Forged Aluminum
Finish - Type 3 Hardcoat Anodized Black
Standard Forward Assist
Standard Dust Cover
M4 Feed Ramps
Charging Handle:
Material - 7075 T6
Machined from Forged Aluminum
Finish - Type 3 Hardcoat Anodized + Teflon Coated for Smoother Operation
Gas Block:
Material - Steel
Style - Low Profile
Size - .750"
Attachment Method - 2x Set Screws + Rockset
Dimpled Barrel
Not Adjustable
Set screws are torqued to 30 IN-lbs. and have Rockset applied for extra security.
Gas Tube:
Length - Rifle
Material - Stainless Steel
Muzzle Device
A2 Flash Hider
MK4 - 18" 5.56 SPR Precision Upper Receiver
Our stated policy is to not accept returns, but if you accidently ordered the wrong item or there was a mistake or if you have any issue at all send us an email (listed in the "contact us" section) and we will work it out.