The relationship among the bullet guide fulcrum, the op rod catch, op rod hooks and clip latch is complex. If it is not correct, a loaded clip will either not release the op rod catch at all when inserted and pressed into the magazine well, release the catch only when excessive force is applied, or release the catch prematurely, causing a mess & possible injury as the bolt is propelled forward under the force of the op rod spring.

The timing gauge gives a precise measurement of the “timing,” that is, when in the process of inserting a clip the op rod catch is released. It is much more convenient than using a loaded clip of dummies (this testing should never be done with live ammo!), and gives a quantitative measure of the release point. If the release point is not within spec, you begin the corrective process by replacing the bullet guide.

I keep a timing gauge in my "gunshow kit" along with my muzzle wear gauge & etc.

Walt Kuleck