Lower Receiver Assembly (AR-9, AR-15, and AR-10/LR108)
Step L4: Bolt Catch Installation
Objective: In Step L4 of lower receiver assembly, we will install the bolt catch assembly onto the lower receiver.
NOTE: This step is not applicable if building an AR-9 on the Aero Precision EPC platform, which is equipped with a proprietary Last Round Bolt Hold Open (LRBHO) mechanism installed from the factory.
Tools Required
1: Only required if building on an Aero Precision Enhanced lower receiver. The Aero Precision Enhanced lower uses a threaded screw to secure the bolt catch to the receiver instead of a roll pin.
2: Required if not building on an Aero Precision Enhanced lower receiver. Other receivers use a roll pin to secure the bolt catch to the receiver.
Components Required
| Quantity | Component |
|---|---|
| 1 | Lower Receiver |
| 1 | Bolt Catch |
| 1 | Bolt Catch Buffer |
| 1 | Bolt Catch Spring |
Instructions:
BEFORE YOU START: Be sure that your magazine catch assembly is properly installed (per Step L3) and that you have verified the magazine engagement and release before you install the bolt catch. You may need to remove the bolt catch if further adjustment of the magazine catch is required.
Step L4.0: Remove Existing Bolt Catch (replacement/upgrade only)
If you are replacing your existing bolt catch (or need to remove the bolt catch for any other reason), first ensure the firearm is unloaded.
Aero Precision Enhanced Lower:
Loosen and remove the bolt catch threaded pin using a 1/16″ hex key. Once removed, the bolt catch, bolt catch buffer, and bolt catch spring will fall free.
Standard AR Lower:
Drive the bolt catch roll pin out of the lugs in the lower receiver using a 3/32″ roll pin finish punch (preferably an offset bolt catch roll pin punch). Once removed, the bolt catch, bolt catch buffer, and bolt catch spring will fall free.
Step L4.1: Lubricate the Bolt Catch Buffer Cavity
Add one drop of wet lube into the bolt catch buffer cavity.
Step L4.2: Remove the Threaded Bolt Catch Pin (as applicable)
If you are using a receiver with a threaded bolt catch pin, remove the pin from the lower receiver.
Step L4.3: Install the Bolt Catch Spring
Place the bolt catch spring into the cavity on the right side of the lower receiver.
Step L4.4: Install the Bolt Catch Buffer
Place the bolt catch buffer into the cavity on the right side of the lower receiver with the rounded end facing outward.
Step L4.5: Lubricate the Bolt Catch Buffer
Place a drop of wet lubricant on the bolt catch buffer using a needle dropper.
Step L4.6: Align the Bolt Catch
Depress the bolt catch buffer and bolt catch spring with the bolt catch. Align the hole in the bolt catch with the bolt catch lugs on the lower receiver.
Step L4.7: Install the Bolt Catch Pin
Aero Precision Enhanced Lower:
WARNING: DO NOT USE THREAD LOCKER.
Feed the threaded bolt catch pin from the rear of the lower receiver, through the rear bolt catch lug, bolt catch, and into the forward bolt catch lug of the lower receiver. Using a 1/16” hex key, tighten the bolt catch pin. Do not overtighten (you will strip the head of the screw or receiver).
Standard AR Lower:
Tap the bolt catch roll pin into the rear bolt catch lug of the lower receiver using a 3/32″ roll pin starter punch (preferably an offset bolt catch roll pin starter punch).
Using a 3/32″ roll pin finish punch (preferably an offset bolt catch roll pin punch) while aligning the hole in the bolt catch carefully, drive the bolt catch roll pin through the bolt catch and into the forward bolt catch lug of the lower receiver until the roll pin is flush with the rear lug.