1928A1 Bolt Hold Open

[spall]

I have a couple of 28A1 lowers, and I get slightly different results between the two with respect to the last round bolt hold open. I'll try to move parts around between them to see if a single part is out of spec (all WWII), but...

With the first, magazine follower engaging the sear trip to its fullest height (not hung up or half engaged, etc), trigger pulled on an empty mag results in full disengagement- trigger goes back smoothly against spring pressure and that's it.

The second (identical scenario) partially engages the sear and skips off, similar to how it disengaged when the bolt/rocker pulls it away in semi-auto. It never pulls the sear down far enough to actually let the bolt go, just enough to make the trigger "click", rather than pull back smoothly.

Which is the intended functionality?

[reconbob]

         I am not sure exactly what you mean, but the best way to check this would be to

pull the trigger and hold it, then push the mag all the way up as far as it goes. If all the

parts are working right the sear should snap up (even though you are holding the trigger)

when the mag is up all the way. But you don't know for sure until you fire the gun. Sometimes

a weak magazine spring can cause it to not work, or the individual parts in the trigger frame.

Also, if the gun short recoils the bolt will not always be held by the sear.

Bob

[spall]

I took a couple of videos to show the difference. Same magazine.

Smooth Pull

Catches Sear

I'll swap trips, then disconnectors, then triggers. Something is different.

I was curious how common this was... I assume the intended functionality is to clear the sear completely.

Edited July 19, 2024 by spall

[gijive]

Try checking the disconnector spring where it engages with the trigger.  It may be broken or shortened.

[spall]

I swapped parts back and forth for an hour... eventually the entire contents of the lower trying to isolate the anomaly. Pivot plate pin hole spacing is identical, yet one lower exhibits one behavior, and the other doesn't, with the same parts swapped between them.

Doesn't really change anything, besides click when trigger pulled on an empty mag. Interesting observation.

[reconbob]

   It is quite common for the sear lever to "nick" the sear dropping it slightly before

additional pulling of the trigger makes the disconnector clear the sear lever and the sear

snaps back. What is supposed to happen is that when the mag is empty, the tab on the mag 

follower pushes the front the sear lever up, which pulls the disconnector out from under the

sear lever and the sear snaps up,  holding the bolt back when the mag is empty.

Bob