AR-15 LPK Takedown Pin Detent Spring

Description

OVERVIEW – PRECISION SPRING FOR POSITIVE REAR TAKEDOWN PIN RETENTION AND FUNCTION

The AR-15 LPK Takedown Pin Detent Spring is the small but essential spring that ensures your AR-15 rear takedown pin stays securely in place, whether your rifle is closed for firing or open for cleaning. Located in the rear of the lower receiver inside the buffer tube detent channel, this spring sits behind the takedown pin detent and applies constant pressure, engaging the detent grooves in the takedown pin. This tension holds your rear takedown pin in both the locked closed position and the open maintenance position, preventing it from walking out, falling free, or getting lost during handling, while still letting you pull the pin with finger pressure when you need to separate the upper and lower.

If this spring is missing, weak, kinked, or has lost tension from age or corrosion, your takedown pin will be loose, wobbly, or will fall out completely — creating an unsafe condition where your upper and lower can separate unexpectedly under recoil. This mil-spec replacement spring is wound to the exact wire diameter, outer diameter, free length, and coil count to provide the correct spring rate for positive, reliable takedown pin retention. Made from high-quality tempered spring steel with a corrosion-resistant finish, it maintains its tension over thousands of open/close cycles and will not take a set, compress flat, or weaken like cheap bulk springs. It is compatible with all standard AR-15, M4, M16, and AR-10 lower receivers using standard takedown pin detents, including forged, billet, and 80% lowers. Whether you are finishing a lower build, replacing a lost spring that launched during installation, or stocking your workbench with essential LPK spares, this detent spring restores correct retention and smooth function to your takedown assembly.

WHY CHOOSE THIS TAKEDOWN PIN DETENT SPRING

The tiny spring that locks your rifle together.

1. Mil-Spec Dimensions and Correct Spring Rate for Secure Takedown Pin Function: The takedown pin detent spring’s job is precision tension. It sits in a small channel drilled from the rear of the lower receiver (accessed by removing the buffer tube or end plate) and pushes forward against the takedown pin detent. The detent rides in the grooves of the takedown pin itself, holding the pin in two positions: fully inserted (rifle locked closed) and pulled out to the stop (rifle open for maintenance). This spring is engineered with the exact mil-spec wire gauge, coil count, and free length to deliver the ideal spring pressure. Too weak and the pin drifts out under recoil or drops out when you tilt the rifle. Too strong and you need a tool or punch to pull the pin, defeating the tool-less field strip design. This spring gives you the perfect balance: positive snap into both positions, firm retention during firing and handling, yet still operable with thumb pressure. The coils are evenly spaced and straight for smooth travel inside the receiver channel without binding or kinking. Each spring is inspected for consistent rate, so your takedown pin functions exactly as designed, every time.

2. Tempered Spring Steel with Corrosion Resistance for Long Service Life: Unlike hardware store springs made from soft wire that flattens after a few months under compression, this detent spring is made from properly tempered spring steel heat-treated for memory and elasticity. It is designed to stay under compression inside the lower receiver for years without taking a permanent set or losing tension. The finish is corrosion-resistant, protecting against moisture, humidity, gun oils, bore cleaners, and solvents that collect in the rear detent channel — an area prone to moisture intrusion around the buffer tube threads. The ends are cleanly finished to prevent the spring from digging into the detent or the end plate and to ensure smooth compression. The spring maintains its length and rate through thousands of takedown cycles, temperature changes, and field use. This is a true mil-spec duty-grade spring built for defense, duty, and high-round-count rifles, not a soft aftermarket substitute that will weaken and cause your takedown pin to walk out at the worst time. It is built to last the life of your lower.

3. Critical Spare for LPK Completion, Lower Builds, and Armorer’s Kits: Every AR builder knows the takedown pin detent spring and pivot pin detent spring are the two most commonly lost parts in a lower build — they are tiny, under spring tension during installation, and launch across the room if your hand slips while installing the buffer tube or end plate. This is why experienced builders keep spares of both on hand. This spring is a direct drop-in replacement for any standard AR-15 LPK. Installation: Ensure the takedown pin detent is in its channel in the rear of the receiver, then insert this spring behind it, and install your buffer tube or end plate to capture the spring, then slide the takedown pin into place. Compatible with all standard takedown detents and takedown pins. Works in all standard AR-15, M4, M16, and AR-10 lowers that use mil-spec takedown components — including forged, billet, and 80% lowers. Whether you lost your spring, are assembling a stripped lower, or stocking your armorer’s bench with essential spares, this detent spring ensures your takedown pin stays secure, functional, and safe.

RESTORE POSITIVE TAKEDOWN PIN RETENTION

The AR-15 LPK Takedown Pin Detent Spring delivers mil-spec tension and corrosion-resistant durability for secure rear pin function.

SPECIFICATIONS

Type: AR-15 LPK Takedown Pin Detent Spring – Rear Takedown Assembly Spring. Material: Tempered Spring Steel – Heat Treated. Finish: Corrosion-Resistant. Function: Applies Pressure to the takedown pin detent for Rear Takedown Pin Retention in Open/Closed Positions. Compatibility: All Standard AR-15 / M4 / M16 / AR-10 Lower Receivers Using Mil-Spec Takedown Pin Detent. Placement: Rear Channel of Lower Receiver Behind Takedown Pin Detent – Captured by Buffer Tube / End Plate.