Common problems with DIY builds

[LRRPF52]

On Saturday at the range, I saw 2 common mechanical problems with AR's that I wanted to give a heads up on:

1. Hammer spring installed upside down, gun didn't work. This showed up first as a walking trigger pin, which told me before I opened the receivers that I was probably going to find an improperly installed hammer spring.






2. Disconnector not timed, resulting in failure to reset trigger. You can do everything right up until function checking the AR15, which most people blow over in a build, and you think everything is fine.

Sometimes, disconnectors will be long on the engagement with the hammer hook where they catch the hammer. When you release the trigger, it won't reset, because the disconnector is still engaged.

When you assemble the lower, do a function check with the lower receiver group before proceeding. This includes:

1. Place the selector on SAFE, attempt to pull the trigger. The hammer should not fall.

2. Place the selector on SEMI, with your hand over the hammer, pull the trigger. The hammer should release. Continue to hold the trigger to the rear, and push the hammer back. It should catch on the disconnector.

3. Release the trigger. The hammer should reset to the trigger/hammer sear, with a metallic click.

4. You should be able to pull the trigger and release the hammer again.

If the hammer does not reset when you release the trigger, it is often too much disconnector engagement that causes this. You can go through several disconnectors, or stone the disconnector until it works, but this is a delicate procedure best followed by someone highly competent. If the surface is not cut square, you will run into early wear and a gun that malfs or doubles or shoots on auto.

[CCinPA]

I ran into this yesterday while installing and setting up the high speed national match "dmr" trigger for my build. It turned out to be that the second stage adjustment was set too heavy, causing the disconnector to not release the hammer upon resetting the hammer.

[LRRPF52]

In my lower pars bin, I keep at least a half-dozen extra disconnectors, in addition to every other lower part.

I can cycle through them until the FCG functions correctly in the rare circumstance that I run into this.

It is especially true with adjustable triggers that allow you to set up the initial take-up and over-travel. JP has excellent instructions on how to set up their adjustable trigger, to include timing the disconnector.