The Primary & Secondary AR-15 and M4 Knowledge Hub organizes practical articles on rifle operation, components, magazines, optics, zeroing, qualification, and long-term performance. Use this page to move from foundational system knowledge to equipment selection and applied range work.
AR-15 and M4 Operation
Understanding the AR-15 Gas System
Learn how the operating system functions, how gas-system variables interact, and how those relationships can contribute to rifle malfunctions.
Rates of Fire for the M4 and M4A1
A practical explanation of slow, rapid, and automatic rates of fire and how those standards apply to the M4 and M4A1.
Magazines and Rifle Configuration
Why PMAGs Are Better Than Aluminum USGI Mags
An examination of magazine geometry, durability, and reliability considerations, including performance with M855A1 ammunition.
KAC SR-15 MOD 2: 10,000+ Rounds Later
A long-term review covering reliability, accuracy, the E3 bolt, extended gas system, URX4 handguard, suppressor use, weight, and value.
What Gun Should I Buy? Prioritizing Firearm Purchases
A framework for deciding which firearms to purchase first and how different weapon categories fit practical defensive priorities.
Optics and Zeroing
The M68 Close Combat Optic
Operational guidance for the M68 CCO, including its controls, mounting considerations, use, and relationship to the weapon’s zero.
Battlesight Zero
Compare common battlesight-zero distances and understand how trajectory and point of impact change across distance.
25m M16/M4 Zero Target
Instructions for using the 25-meter M16/M4 zero target and translating shot-group location into sight adjustments.
How To Zero the Laser Boresight to a Weapon
A step-by-step explanation of setting up the military laser boresight, locating the true line of bore, and refining its zero before adjusting an optic or laser.
Qualification and Range Application
Standard Qualification for the M4
An explanation of the 2017 TC 3-22.9 qualification framework, the appropriate use of ALT-C, and the known-distance alternative course.
How to Use This Collection
Readers new to the platform can begin with the gas system, magazines, and firearm-purchase framework. Those preparing for range work can continue through the M68, battlesight-zero, 25-meter target, laser-boresight, and qualification articles. The SR-15 longevity review provides a detailed example of how design choices and components perform together over extended use.