The Heckler and Koch buffer retainer spring (HK part no. 50233121) is a factory replacement part for HK416/MR-series rifles, the small spring that keeps the buffer retainer seated and under tension inside the lower receiver. It’s an easy part to overlook until it weakens or goes missing, at which point the buffer retainer can fail to hold properly and cause function issues. Armorers and HK416/MR owners performing routine maintenance or replacing a worn retainer spring need this exact factory part rather than a generic AR-15 substitute, since HK’s system doesn’t share every small part with a standard mil-spec lower. It’s a low-cost part that keeps a critical retention system working the way HK designed it.

Key Specifications

• Factory replacement buffer retainer spring for HK416/MR-series rifles.
• Keeps the buffer retainer under proper tension inside the lower receiver.
• Genuine Heckler and Koch factory part, not a generic AR-15 substitute.
• Ideal for routine maintenance or replacing a worn or missing spring.
• A small but essential retention component for reliable function.

Frequently Asked Questions

Will a generic AR-15 spring work instead? HK416/MR-series rifles use HK-specific small parts in some areas, so the genuine factory spring is the safer choice.

How do I know if this spring needs replacing? A weak or missing retainer spring can let the buffer retainer fail to hold properly, causing function issues.

Is this an easy part to install? It’s a small internal spring; armorers and experienced owners typically handle this as routine maintenance.

Buy the HK Buffer Retainer Spring

Keep your HK416/MR-series rifle’s buffer retention working as designed. Order the Heckler & Koch / H&K retainer spring from our rifle parts lineup, and our Lubbock, Texas team can help confirm compatibility before it ships.