How a Faulty Receiver Can Ruin Your Trigger

By Kevin Muramatsu

Incorrect Distance Between Trigger Pin Holes

The trigger pin holes in the receiver have very specific dimension and separation. There is no appreciable run-out regarding their interrelation. There is only a 1.5 thousandth of an inch tolerance in their size.

Now, out-of-spec hole placement on some receivers might not cause conflict with certain off-the-shelf factory trigger packs. This won’t be the case with a standard JP match trigger, though. JP triggers are highly refined and precisely formed match-grade machinery.

This makes it more important to have a decently made receiver to install them in.

If the pin holes are too close, the sear angle will not be ideal. The hammer and sear are supposed to interact in a specific way. When the pin holes are too close together, their relationship is altered, and the possibility of a drop fire increases.

Just as importantly, it quickly becomes impossible to properly time the disconnector. The hammer becomes over-rotated, and the disconnector catch on the hammer comes too close to the disconnector. When the trigger is pulled, the disconnector hits the hammer prior to release, and you effectively now have a two-stage trigger.

When the holes are too far apart, the hammer is not sufficiently rotated. This again causes the sear interface to be less than ideal. In this case, the trigger pull will be slightly higher.

This will also impart a greater amount of wear to the sear. After releasing the disconnector, the hammer has to “jump” a greater distance to reset, and this slamming of the hammer notch onto the sear will cause premature wear.

A similar effect is often found in factory units. This is the symptom of very different sear geometry and the desired (i.e., significant) amount of sear engagement inherent in the factory trigger parts. This greater sear engagement (and pull weight) of a factory trigger is a deliberately conservative choice. The intent is to make bump fires and accidental discharges less likely, particularly for inexperienced shooters.

It should be noted that the occurrence of faulty receivers like those I’ve discussed has been quite low and tends to be quite brand-specific. The most well-known brands of receivers rarely if ever demonstrate these problems.

Ultimately, the quality of your receiver should match the quality of the trigger you put in it.

Should your installation of JP parts demonstrate any such issues, call their tech help extension for assistance. In my years working there, I saw it all, so don’t feel embarrassed. And feel free to send in your receiver for an expert, custom installation of your JP match trigger kit.