Lapping an AR15 Upper Receiver

November 23, 2012 Bill Marr Rifles, Tutorial 0

This is our stripped YH upper and a lapping bar designed for AR15 type rifles.
Lapping an AR15 upper receiver ensures that the barrel is true to the upper receiver by providing a perfectly perpendicular surface for the barrel extension.  This task is easily accomplished with a few simple tools and a handheld drill.
For this project, Brownells supplied us with the following:
This is our stripped YHM upper and the AR15 lapping tool.
The lapping bar requires silicon carbide abrasive. 180 grit is recommended.
The upper is secured in a set of blocks from our Critical Tools Kit. The portion that contacts the inside of the upper is coated in oil. Once inserted, the 180 grit abrasive is placed on the contact surface of the lap. NOTE: It is critical that the abrasive does not enter the inside of the receiver.
We use a power drill to turn the lap and contact the face for a few seconds. We look at the face to assess progress and then contact again as needed. Ideally, you want at least 80% of the surface lapped.
Here is the finished surface. The front of the receiver is now completely true.

 

 

 

Related Articles

Accessories

Rogers Super-Stoc Review

July 30, 2012 Bill Marr 0

Rogers Super-Stoc Review   Designed by Bill Rogers, former FBI agent, inventor of the Kydex holster and founder of the premier shooting school in the United States; the Rogers Super-Stoc is designed to fit your […]

Carbine Basics

Daniel Defense M4 Upper Review

November 1, 2012 Bill Marr 0

We headed to the range with the upper receiver we built here.  This build was based on a Daniel Defense stripped M4 style carbine length gas system 16″ upper.  We added a Daniel Defense Lite Rail 9.5 FSP, Larue […]