According to Wikipedia:

Rifling refers to helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis. This spin serves to gyroscopically stabilize the projectile, improving its aerodynamic stability and accuracy.

Rifling is often described by its twist rate, which indicates the distance the rifling takes to complete one full revolution, such as “1 turn in 10 inches” (1:10 inches), or “1 turn in 254 mm” (1:254 mm). A shorter distance indicates a “faster” twist, meaning that for a given velocity the projectile will be rotating at a higher spin rate.

In layman’s terms, the lands are the raised spirals inside the barrel of your AR. The grooves are the “ridges”.

When the bullet travels down the barrel after being fired, it uses the lands and grooves to create spin (twist referred to earlier), which affects accuracy, distance, and trajectory.

Learn more about lands and grooves in our blog about Barrel Rifling by clicking here!

A good example of lands and grooves in a Royal Ordnance L7 Tank Gun.

A good example of lands and grooves in a Royal Ordnance L7 Tank Gun.

The lower parts kit for an AR-15 usually contains all of the pins/detents and springs necessary to complete the lower receiver.

Some lower parts kits will omit the fire control, safety, and pistol grip – or may exchange/upgrade these items for better-than-mil-spec quality parts.

Traditionally, a complete lower parts kit contains:

    • Bolt Catch,
    • Bolt Catch Plunger,
    • Bolt Catch Roll Pin,
    • Bolt Catch Spring,
    • Buffer Retainer,
    • Lower-Parts-Kit

    • Buffer Retainer Spring,
    • Disconnect,
    • Disconnect Spring,
    • Hammer,
    • Hammer Pin,
    • Hammer Spring,
    • Magazine Catch,
    • Magazine Catch Button,
    • Magazine Catch Spring,
    • Pistol Grip (A2 style),
    • Pistol Grip Lock Washer,
    • Pistol Grip Screw,
    • Pivot Pin,
    • Pivot Pin Detent,
    • Pivot Pin Detent Spring,
    • Selector,
    • Selector Detent,
    • Selector Detent Spring,
    • Takedown Pin,
    • Takedown Pin Detent,
    • Takedown Pin Detent Spring,
    • Trigger,
    • Trigger Guard,
    • Trigger Guard Roll Pin,
    • Trigger Pin,
    • Trigger Spring