Looked up the post I’d found earlier regarding a person that cut 2 coils and resolved same issue. Reading it again I realized they had a rifle buffer spring in a carbine buffer tube, so not applicable.
The fender washers are 0.050" thick. With 2 washers installed the bolt would not come back far enough for the catch to engage. With 1 washer installed there was marginal improvement, but still not acceptable to me.
The question has not been asked, but this is the reason this bothers me: When a magazine is emptied, the bolt locks back just like it should. When inserting new loaded magazine, the bolt releases on it’s own. Sometimes it releases before the new magazine is fully engaged and therefore does not load/chamber the top cartridge. It is a nuisance to either do a press check, pull the trigger and see what happens, or eject a loaded cartridge. In addition, having the clear flag snapped off when the range is cold is very startling to hear.
I have observed the catch is sloppy on the installation pin. It is rotated counterclockwise in this photo. It looks worse in person:
Didn’t take a photo, but I filed about 0.125" off the threaded end of the buffer tube to get a couple more threads deeper, effectively shortening the buffer tube 1/8". The photo shows I need to do a better cleanup of the filings
Edit: I have some #4 SS washers, but they are too thick as well as too large of an OD to shim the slop out. I understand the AEG gear box shim kits work well, I might try one of them. In the meantime I am going to focus on the geometry of the bolt catch itself to see if there is some improvement available via filing.
Yeah that bolt catch needs to come up more. On 3 of my rifles/pistols it comes up so that there is only a sliver of space showing between the two lower locking lugs. Do you have the correct spring in the bolt release catch hole? There are a couple in the LPK that could be mistaken for each other.
Thanks @Craig6, I actually tried it without the spring and plunger. Doing honey-dos today, but need to take a look to see if I can remove some material to allow it to swing up higher. Haven’t had time to look at it again, but expect to see it is hitting the inside wall of the receiver too soon.
Since I bought an “oops” kit, I have 2 trigger disconnect springs, 3 bolt catch springs, and 2 bolt catch plungers. Either the lower kit or the oops kit must have thrown in an extra bolt catch spring. I have compared the 3 springs and the 2 plungers and see no visible discrepancies. I have blown the hole out (in the receiver) to be sure there is no debris. I have tried multiple combinations of the springs and plungers and the results are always the same; I even tried the spare trigger disconnect spring for comparison, and still same results.
@Gary_H SOMETHING is keeping that lever from coming up to fully engage the bolt. When you mash the bottom half of the release does it go all the way up? Is the allen screw too tight (You said M4E1 lower)? Is the actual bolt stop/release correct? Grasping at straws here. ANY AR platform will go to battery if you bounce the butt stock off the deck but that is inertia and gravity. Do you have more than one magazine? Bad follower?
Locks and holds the bolt back securely with all three magazines I have tested it with.
Just got a minute to look at it. No photos because my phone is on charge, but based on wear pattern and general eyeballing it , it looks like it is being restricted by contact with the inner wall of the upper receiver. Just got to take the catch out one more time, file some material away and retest it. I have a high confidence this has been the issue from the beginning. Will report back …
Depending on what you spent, and are willing to spend on your build I highly recommend JP Enterprises close captured spring systems. They’re an easy drop in, quiet and smooth operation with options for adjusting spring tension and buffer weights.
Can’t hate that! JP has become my go-to buffer assy for higher end builds. That buffer combined with a good adjustable gas block and you can tune damn near all the recoil out.
I am going to call it worst case tolerance stack up. All it took was filing 0.006" off the right place on the bolt catch. I continued to think about @Craig6 saying
What was holding it back was the bottom “lock button” was bottoming out against the lower reciever. So either the pivot hole was drilled slightly off, the receiver was milled slightly off, or something else, but I am glad this is over Don’t know if 6 thousands was exact right amount to remove, but it worked.
Don’t know if 6 thousands was exact right amount to remove, but it worked.
