I just finished building my first stripped lower and am having a small issue with my bolt catch. If I insert an empty mag into the magazine well with the bolt closed, and cycle the bolt all the way to the rear, my bolt catch does not get pushed up by the magazine follower, thus letting the bolt close on the empty mag. It will do this on 2 different PMAGS that I know for a fact functioned in my old M&P15. However, with the bolt open (or with the lower seperated from the upper), an empty magazine will push the bolt catch up with no problem. When I installed the bolt catch, I put the spring and buffer in correctly (kind of hard to screw that up). I am not a gunsmith and am wet behind the ears when it comes to building ARs, so I dont know why this is happening. Any ideas as to why this might be going on?
With just the lower insert an empty mag, and see if the follower is pushing up on the bolt catch.
The spring in the bolt catch could be a bit stiff, and the mag doesnt have enough force to push the bolt catch up.
Also look at the little pawl that the follower actually hits. If its too short the follow could slip around it, and not make good contact with the follower.
If nothing else you can get new parts, and see if that doesn’t fix it. I had one lower a long time ago with similar issues, and replacing the spring fixed it. (BC spring). Sometimes they can be a bit stiff. Brownells sells Colt parts, and you could replace the entire BC mechanism for maybe 30 bucks. Or contact Grant, and see if he can’t get you some replacements.
I also have a used BC mechanism with the spring, BC, and little black plunger thingy if you’re interested in trying that. They are LMT parts I just replaced with Colt parts.
I am definately seating the magazine all the way. And like I said, with the upper removed from the lower, the magazine follower pushes up on the bolt catch just fine with no binding or anything. My first thought was a stiff spring, but the fact that the problem only happens when the upper is on the lower makes me think otherwise. With just the lower, the bottom of the “ping pong paddle” (the part you press to manually lock the bolt back) moves smoothly, and returns to its original position after being depressed just fine. Also, I forgot to mention that I can manually lock the bolt with no problems.
Here is a question, that if answered, may help me:
For those of you with properly functioning bolt catches, if you seperate your upper from your lower and insert an empty magazine (PMAG), what happens when you push the ping pong paddle as you would do when releasing the bolt in a reload? Does the magazine sprong/follower have enough umph to move the bolt catch back up into its original position, or does it stick in the downward position? Remember, this is on an empty mag. When I do this, my bolt catch sticks in the downward position until I push the bottom of the ping pong paddle in, as if I were manually locking the bolt to the rear.
One more thing I forgot to mention is that with just the lower, the magazine follower will push the catch up all the way, to the point where it could not move up any further due to touching whatever part of the lower reciever casting limits its range of movement.
How tight it the bolt catch in the lower receiver? Could it be binding enough that the extra pressure of the bolt/carrier riding it keep it from moving freely? The other thing that comes to my mind is could you have switched the BC spring with one of the take down pin detent springs?
It pushes it back up, to the highest possible position. That goes for pmags and all others. It is the magazine spring that pushes it back up. Try this and push down on the mag follower and see what happens.
Try some USGI magazines.
Looking at the rear of the magazine follower, the tip of the bolt catch rests on the very edge of the follower when pushed up. Some magazines have more “meat” on the follower to engage the bolt catch, some magazines have less “meat” to the follower.
USGI magazines seem to have more surface for the bolt catch to engage. PMags seem to have less area because the body of the magazine is thicker and does not allow as much area for the follower to hit the bolt catch. When there is not enough surface for the bolt catch to engage, being pushed up by the magazine follower, the bolt catch slips behind the follower. This defeats the purpose of the bolt catch and the magazine does not lock the bolt open.
Try another magazine that has more follower surface (USGI). Also, try another bolt catch. If USGI mags work and others do not, that is one fix—only run USGI mags.
If that fails, you can always fabricate another bolt catch to fit this receiver…This was a fix for a mis-machined receiver, my PMags worked fine in every other rifle but this one. So its not a slam on Magpul, just a way to get this troubled rifle to work better.
…(here)
All the same receiver, but different magazines/followers:
#1 Shows a 30 rnd PMag, follower missing the bolt catch #2 Shows a 20 rnd USGI magazine, follower missing the bolt catch #3 Shows a large gap mis-machined in the bolt catch area, lots of slop. #4 Shows 30 rnd USGI magazine follower hitting the bolt catch
The protrusion on the left side of the catch has plenty of contact with the follower. Thank you very much for the photos.
You guys are going to call me an idiot for not figuring this out before posting a thread about it, but here goes:
I am pretty sure I have heard of this problem before, but didn’t think about it until I figured out it was the root of my troubles. The right hand side front edge of the bolt catch is rubbing on the little lip on the back or “spine” of the PMAGs, causing just enough friction to bind the latch and keep it from springing up when the magzine follower hits it. Looks like I need to file off just a hair of the bolt catch so that it will clear the PMAGs. Or I could just modify every single PMAG I ever intend on running in this weapon…
I have always been told to alter the cheaper part, but I want this gun to run any damn magazine I put in it. Am I right by filing a smidge off of the bolt catch in order to achieve this?
I just checked mine and wow it couldn’t be any closer with the Pmags, all the other USGI mags have allot more clearance. I would probably mod the bolt catch one hair at a time. Let us know how it works out, good luck.
I will let you know how it goes. It wont take much at all. I actually found that if I grabbed the bottom of the mag while it is inserted in the gun and pulled it back, it would take the pressure off the catch and the follower would pop it right up. Another wierd thing is that it only hangs up when the mag is empty. When there are rounds in the mag, the catch and the lip dont touch at all.
I would just lightly modify each of the PMags that are not running in your rifle right. Easier to file/cut a small amount off of the rear opening of the magazine than to shave or fit a new bolt catch. It is going to be a very small amount and it will not seriously hurt the magazines.
This is a good reason to test run each magazine fully before counting on it
I tried filing the bolt catch this morning. 45 minutes using 6 different files and I could not remove one damn bit of the metal from it. That is some hard steel! I did go ahead and file all of the PMAGS in my stash and they now work like a champ, however I would still like to get a new bolt catch in there. I contacted Grant at G&R and he helped me determine the manufacturer of the bolt catch, and I contacted the company (LMT). They told me to send it in and I can get a replacement. So all is good in the hood. Except for that I am probably going to f**k up my Noveske lower getting the pin back out.
