How to Install a Shotgun Scope Saddle Mount on a 12GA 870

By Texas Precision Optics Inc | Published: 2026-10-27

Category: How-to Guides

Learn how to install a shotgun scope saddle mount on your 12GA 870. Step-by-step guide for the TPO M87 mount, including alignment, torque, and common mistakes.

Quick Answer

Install a shotgun scope saddle mount on a 12GA 870 by removing the trigger assembly pins, sliding the mount into place, and tightening the screws evenly. The TPO M87 mount fits directly without drilling.

Why a Saddle Mount Works for the 870

A saddle mount wraps around the receiver instead of replacing the trigger assembly pins, so you don't need to modify the shotgun. The TPO M87 is designed specifically for 12GA 870 models and uses the existing trigger pin holes for a secure fit.

Because it's a one-piece aluminum alloy mount, it stays rigid under recoil and provides 14 slots for eye relief adjustment. This gives you flexibility to position a scope or red dot exactly where you need it.

Tools You'll Need

You only need a flathead screwdriver or a small punch to push out the trigger assembly pins, and a Torx T15 or T20 driver (check your mount's screws) to tighten the mount. A torque wrench set to 15–20 in-lbs is optional but recommended for consistent tightness.

Installation Steps

1. Unload and Clear the Shotgun: Remove the magazine tube cap and ensure the chamber and magazine are empty. Verify visually and by feel. This is non-negotiable for safety. Always double-check the chamber even if you think it's empty.
2. Remove the Trigger Assembly Pins: Use a punch or flathead screwdriver to push out the two trigger assembly pins from left to right. Keep them in a safe place—you'll reuse them later. Don't force the pins; if they stick, tap gently with a plastic mallet.
3. Position the Saddle Mount: Slide the TPO M87 mount over the receiver from the top. Align the mount's holes with the trigger pin holes. The skeleton slotted side walls should face outward. Make sure the mount sits flush against the receiver; gaps mean misalignment.
4. Reinstall the Trigger Pins Through the Mount: Insert the original trigger pins back through the mount and receiver. They should slide in smoothly. If they bind, adjust the mount position slightly. The pins must pass through both the mount and receiver without force.
5. Tighten the Mount Screws Evenly: Use a Torx driver to tighten the two screws on the mount's sides. Alternate between screws in small increments until snug. Torque to 15–20 in-lbs if using a wrench. Over-tightening can strip the aluminum threads or crack the mount.
6. Attach Your Scope or Red Dot: Use the 14 slots on the mount to position your scope rings. Slide the scope forward or backward for proper eye relief before tightening the ring screws. Leave the ring screws slightly loose until you confirm eye relief and level.

Product Details

TPO M87 Shotgun Scope Saddle Mount for 12GA 870: Fits 12Ga Shotgun with a lower weight design and skeleton slotted side walls. One piece mount made of high quality aluminum alloy. The lightweight design reduces added heft on the receiver, while the 14 slots let you adjust scope position without swapping rings.
TPO M87 Shotgun Scope Saddle Mount for 12GA 870