What AR15, M16, and M4 Parts and Accessories Can I Buy at OperationParts.com?

Updated

OperationParts.com is an online retailer that sells AR15/M16/M4 parts and accessories, along with gear for other firearm platforms. Its catalog is organized around build and upgrade categories: upper and lower receiver components, handguards and rail systems, stocks and grips, iron sights and optics mounts, magazines, and armorer tools. If you are building, upgrading, or customizing an AR-pattern rifle, the site carries both general parts and a notable selection of Knight's Armament (KAC) products. Availability varies by item—some products are in stock and can be added to cart, while others show as out of stock or "read more" without a purchase option.

Upper receiver parts

The upper receiver section covers the parts you would replace or add when configuring the front half of an AR15/SR15 or AR10/SR25 pattern rifle:

  • Complete uppers
  • Upper receiver parts
  • Gas blocks, muzzle devices, and barrels
  • Handguards / rail systems and accessories
  • Suppressors

The same category structure repeats for the AR10/SR25 platform, so you can filter by large-frame versus small-frame parts. A listed example is the Allen Engineering Recce Barrel Kit, 16.5″ at $600.00, which is an upper-related barrel kit.

Lower receiver parts

The lower receiver section includes:

  • Lower receiver parts
  • Lower receivers
  • Stocks, grips, and accessories

A listed example is the KAC-Knight's Armament SR-15 IWS Lower Build Kit BLEM at $648.00. Note that this item currently shows as out of stock, so a lower build kit may not be immediately purchasable depending on inventory.

Furniture, sights, and optics

Beyond receivers, the site groups the accessories that affect handling and aiming:

  • Handguards / rail systems — including items such as the KAC 5 Rib Handguard Panel, 3.47 Inch Length at $27.99
  • Stocks and grips — for example the Magpul MOE SL-K Carbine Stock – Mil-Spec at $42.70
  • Iron sights (BUIS) — front, rear, and night sights
  • Optics and optic accessories — including optic mounts and modular attachments such as the KAC Leupold Delta Point Pro Modular Scope Cap Attachment at $218.81

Magazines, tools, and other gear

The catalog also lists:

  • Magazines and mag accessories
  • Armorer tools
  • Cleaning and lubrication
  • Training aids
  • Bipods, mounts, slings, and sling mounts
  • Lights, lasers, and their mounts

Platform-specific sections exist for bolt guns, CZ Scorpion, H&K, M-14, M249, SCAR 16/17, shotguns, and pistols, so the store is not limited to AR-pattern rifles.

Complete rifle systems and larger builds

For buyers who want a factory-configured option rather than assembling from parts, the site lists complete systems such as the KAC-Knight's Armament 5.56 SR15, KS4 Rifle System, 16″ at $2,999.52, and the KAC-Knight's Armament SR-25A3 Upper Receiver Kit, 22″ Barrel with a price range of $3,456.00–$5,024.25 depending on the variant selected.

What to check before buying

  • Platform compatibility — confirm whether the part is for AR15/SR15 (small frame) or AR10/SR25 (large frame), and whether it is Mil-Spec where relevant (for example, the Magpul SL-K stock listing specifies Mil-Spec).
  • Variant selection — several products have multiple variants; the price and fit depend on the option chosen.
  • Stock status — some items are marked out of stock or show "read more" instead of "add to cart," so verify availability before planning a build around a specific part.
  • Brand-specific parts — a large portion of the catalog is Knight's Armament products, which may matter if you are matching an existing KAC build or prefer a different manufacturer.

The site's stated focus is "Build. Upgrade. Customize." across rifle, shotgun, and pistol essentials, with fast shipping on gear and accessories. For a build or upgrade project, the practical starting point is to identify your platform (AR15/M16/M4 versus AR10/SR25), then work through the upper, lower, furniture, sighting, and magazine categories in order.