What Are the Parts in an MP5 Bolt Carrier Group?

The bolt carrier group of an HK MP5, which is the heart of the action’s infamous roller-delayed blowback operation, comes apart in a couple of pieces.

The bolt group houses these pieces, which are responsible for feeding, locking the action, firing, extracting, and ejecting spent casings. Here’s what the main components are.

The MP5 Bolt Carrier Group Itself
The MP5 bolt carrier group is a metal component that carries the bolt body and also communicates with the recoil rod and spring, storing energy to return and reset the acton after firing the gun.

The bolt carrier group also contains rails that serve as an interface between the group and the MP5’s receiver. The bolt carrier group should be kept clean and well-lubed to ensure fluid operation, minimal friction and wear, and to protect against corrosion.

MP5 Bolt with Rollers, Extractor, Ejector, and Springs
One of the main components of the bolt carrier group itself is the MP5 bolt, a roughly cylindrical, small metal piece that contains the extractors, ejectors, springs, rollers, and which houses the locking piece with the MP5 firing pin within it.

The bolt is a cylindrical metal body that contains a hollow for the locking piece, which helps control the rollers, as well as contain the firing pin.

The rollers, which protrude from the sides of the bolt body, fit into recesses in the barrel trunnion, providing a delay after the cartridge is fired before they disengage and allow the bolt carrier group to move rearward.

The bolt itself also contains the extractor, ejector, and associated springs which extract and eject spent cartridges.

The Locking Piece
The MP5 locking piece is a small metal component that houses the firing pin and which fits into the bolt body.

Basically, the locking piece is a timing piece that “tells” the bolt how long the rollers should remain locked in the barrel trunnion before allowing them to roll back and cycle the action.

The MP5 Firing Pin and Spring
Inside the MP5 locking piece is the MP5 firing pin itself, a small metal cylinder with a pointed head, driven by a spring. This is the component that actually strikes the base of the 9mm cartridge, igniting the primer.

The firing pin itself must be properly heat-treated in order to prevent deformation at the tip which will compromise primer ignition. Ideally, it should also be treated with a corrosion-resistant finish to protect it.

Zenith Firearms: High-Quality, USA-Made MP5 Parts
Looking for high-quality MP5 parts to make repairs, upgrades, or replacements to a German HK MP5?

Visit Zenith Firearms. They carry a wide range of MP5 parts and accessories, designed for their American-made MP5, the ZF-5, but which are compatible with Heckler & Koch MP5, MP5K, and SP5K platforms, along with other 9mm roller-delayed blowback firearms such as MP5 clones.

Their MP5 parts are made with high-quality steel, heat-treated, and many of them are finished with wear and corrosion-resistant manganese phosphate coatings to improve durability and longevity.

Moreover, they make a wide range of USA-made parts, which helps ensure 922(r) part compliance.

For more information, visit their website via the link above or get in touch with them at [email protected].

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