M4 lower problems

[nick060200]

I put together a cheap m4. The upper and lower don't mate right. The front take down pin goes in like it's suppose to but the rear pin is too hard to push in by hand.

It's not the upper because it goes on both my other m4's fine. And yes the lower is all put together correctly.

The tolerances are off a hair. Is this common and is there a specific place that material can be taken away to correct the issue?

Also when I push the rear take down pin in 1st it goes in fine then the front pin can't be pushed in by hand.

Any suggestions?

[bdriller]

I have had the same problem,the lower I had the metal was a little high behind the front pin took a little off and no more problem just take your time and see where the fit between the upper and lower is to tight and file it down

[GunLawyer001]

I put together a cheap m4. The upper and lower don't mate right. The front take down pin goes in like it's suppose to but the rear pin is too hard to push in by hand.

It's not the upper because it goes on both my other m4's fine. And yes the lower is all put together correctly.

The tolerances are off a hair. Is this common and is there a specific place that material can be taken away to correct the issue?

Also when I push the rear take down pin in 1st it goes in fine then the front pin can't be pushed in by hand.

Any suggestions?

Try the upper and lower separately on different receivers, see which one is more non-standard. File away at that one.

Also, assemble them against a strong back light, see where the receivers touch first.

If you don't have access to any known-good receivers, send me a PM.

[iamtommyboy]

Had the same problem when building my brother's a few months back. Had to shave a hair off of the ear on the upper where it meets in the rear. Tiny bit at a time until it fits. Works like a champ!

[Gun]

Tap the pin in with a brass or nylon hammer. Had one that needed this, and after a while I could push the take down pin out with my thumb.