Swap in new mag catch, but mags dont engage. WTF
 

Hello all!

I recently bought a new King Arms M4 mag catch to replace the ICS one that wore out. The King Arms did not fit at all at first, frustratingly enough.. so I sanded and slightly dremeled it to a perfect fit, it pushes in and out smoothly.

Now the problem, none of my M4 magazines securely fit anymore. I have 3 TM metal mags, Two Dboys metal mags and one King Arms Metal magazine. All of these had fit perfectly and fed nicely with the original ICS mag catch. Now, for most of them I am able to pull them out without even touching the mag release. The Dboys fit okay.. but slightly wobble.. yet they are the only ones that seem to feed without intervention (ie. pushing the mag upward).

So what the hell? The mag catch seems to fit perfect and the little block which snags the square space on the magazine protrudes enough inside the magwell.. I don't understand why the magazines wont engage. I've tried SLIGHTLY elevating the top or bottom of the square block area on one mag but that didnt really solve the problem either.

Any ideas?

You could try a couple things. I am not totally sure what you mean by elevate the square box area some explanation would help.

I have had success with a flat head screwdriver, you place it the square hole you reference and gently apply pressure and force the top of the mag out slightly. This may be what you are explaining.

You seem to have a sloppy mag well which may not have been a problem for your original mag catch. Velcro on the side opposite the catch may move the mag over enough to create a positive engagement. Also a little at the rear of the mag well can address the feeding issue. Use the fuzzy side of the Velcro and a little patience.

Beyond that you might need to add some material to the catch itself or buy another one and see.

Remove the new mag catch and re-install the old one.
You said it was worn down. When you insert a magasine in the rifle, can you feel some play up-down with the old one?

If not, put both mag catch side-by-side. I bet the KA one has the locking block just a bit higher... say half a millimeter.

The old ICS one has threading for the button screw that are completely worn out, the screw literally just spins freely when I try to tighten it. As well, no magazine had any kind of play with the ICS magazine catch.

not all manufacturers use the same specs. Especially when you are looking at King Arms and ICS.
You're problem does not surprise me at all, in fact I would have been surprised if it DID work.
M4's especially are horrid when it comes to mix + matching manufacturers. This is why many armalite owners have mag seating issues and can only stick to certain brand mags

Try to look for an ICS Catch.

Just as I though. I removed my ICS mag catch to make sure.

Take the round part/post in your left hand with the catching part on your right. Look at the block that catches the mag. See it's a millimeter lower than the upper edge?

The KA one is flush with the top.

Now you know what to do. A dremel will fix is in no time, but I recommend a good old metal file for that job.

Upon closer inspection, I noticed that too. This fucker is going down.

All it takes is a bit of filing, I purchased the Ambidextrous King Arms magazine catch and had to remove about ~.5mm of material from the top of the catch and now my Magpul PTS magazines fit like a dream.