msrx-usa.com
How It Works
The Corrective Adjustment Mechanism (CAM) rear takedown pin simply takes advantage of the mil-spec tolerances of the lower receiver and takedown pin, as well as the oval shape of the hole in the upper receiver lug. By bending the modified rear takedown pin a few thousandths of an inch, we are able to bring upper and lower receiver halves together.
The CAM rear takedown pin acts as a typical mil-spec pin until rotated, so you can swap any upper onto a CAM equipped lower, even if that secondary upper fits differently than the primary upper.
The Height
The hole in the rear lug of the typical AR upper receiver is the same height as the diameter of the rear takedown pin holes of the lower receiver, as is indicated at .250"
The Width
However, the hole in the rear lug of AR upper receivers is oval, rather than round. This is done to allow tolerance so that uppers and lowers from different manufacturers can be mated. This also allows room for the CAM to operate.
Sloppy loose?
To address loose fitments, the bend of the .002 through .008 compensation CAM rear takedown pin is oriented as indicated by the green arrow when upper and lower are adjoined and the rear takedown pin is initially seated. The black circle of the diagram indicates the takedown pin hole in the lower receiver. The red oval indicates the hole in the lug of the upper receiver.
The Cure!
When the CAM is rotated 90 degrees, the bend in the pin forces the lug of the upper receiver downward, clamping the upper and lower together. Corrective Adjustment Mechanism rear takedown pins can correct receiver gaps up to .008" wide.
Hammer Tight?
The CAM also offers relief from fitments that are so tight as to require undo force to seat a rear takedown pin. This occurs when the hole in lug of the upper (red oval) doesn't extend far enough into the lower to line up with the holes in the lower (black circle) as shown. The #0 (zero) CAM pin has an upward bend when initially seated, as indicated by the green arrow, allowing it to arc over the bottom of the out of spec hole in the rear lug of the upper and easily pass through the hole in the opposite side of the lower. No hammer required!
The Result!
When the -0- CAM pin is rotated 90° after being seated, the upper and lower receivers are drawn back together and locked down. If you have other uppers that share the same lower receiver that do not fit as tight, no worries, the -0- rear takedown pin acts like a typical mil-spec pin when rotated to this position.
The Channel
To make it possible for the CAM to function, we extend the detent channel at a 90° angle for a quarter of a revolution, at the end of which a divot is placed to capture the detent.
The Press
After the detent channel has been milled, each CAM rear takedown pin is placed in the hydraulic press and shaped to the desired amount of correction. Once done, the end of each pin is marked with the amount of compensation for easy identification.
The Finished Product
It doesn't take much, to get the job done. This is a finished #8 CAM pin, which will tighten an AR upper/lower receiver gap of up to .008" wide, and is the maximum amount of correction available.
