M4 build problems > Build It Yourself

Posted: 7/4/2008 4:09:18 AM EDT

I recently finished a M4 build and spent the last two days shooting it. I ran into a few problems. Once in awhile I get a feed jam. Sometimes on loading from a open bolt and sometimes right in the middle of a mag. Not often.. ejection is forward and once inawhile one case just dripples on to the table. Finally at the end of the day yesterday a empty case got stuck in the chamber.
I got the case out and took it down to my shop. I found the extractor spring was thicker and heavier than a spare I had and had a black bumper. I replaced it with the lighter spring with a blue bumper. The gas rings would not hold the carrier when I stood it up on the bolt , so I replaced it with a Mcfarland gas ring. and I polished the feed ramps lightly with the dremel.
I noticed a bunch of Brass particles in the locking lug recess of the barrel.
Anybody got any other Ideas?
The mags are fine and I shot a few differant brands of ammo. Both worked 100% in my other m4.

Posted: 7/4/2008 6:15:56 AM EDT

[#1]

Quoted:
.. ejection is forward and once in awhile one case just dribbles on to the table. Finally at the end of the day yesterday a empty case got stuck in the chamber.

Have you ensured the chamber is clean? What type of ammo are you using? Does your ejector move smoothly?

I got the case out and took it down to my shop. I found the extractor spring was thicker and heavier than a spare I had and had a black bumper. I replaced it with the lighter spring with a blue bumper.

The thicker extractor spring is actually better, especially if your experiencing failures to extract. You may want to re-install the thicker spring and possibly add an extractor o-ring.

The gas rings would not hold the carrier when I stood it up on the bolt , so I replaced it with a Mcfarland gas ring.

The way to properly check the condition of the gas rings, is to first separate the bolt and carrier. Now re-insert the bolt alone into the carrier, and holding the assembly upside down, see if the rings will hold the weight of the bolt.

I noticed a bunch of Brass particles in the locking lug recess of the barrel.

The brass particles are a normal part of new rifle break-in, and are probably coming from your extractor.

Anybody got any other Ideas?

So, for an over view:

1- Ensure the bolt and carrier are properly lubed for break-in. I like to go a bit heavy with the lube during this time.

2- Re-install the heavier extractor spring for starters. An o-ring might not be necessary at this point, but could be added insurance later on.

3- Clean the chamber with a GI chamber brush and solvent.

4- Ensure your ejector operates smoothly, apply a drop of lube IAW the Army -10 Operators manual.

5- Re-install your old gas rings, and check for serviceability.

Posted: 7/4/2008 6:06:53 PM EDT

[#2]

Might not hurt to try a brand new mag as well. I've had worn out mags that would not feed into my rifle, but they would work fine in another guys weapon. You are good to go on the McFarland gas ring. I use them in all of my AR's.

Posted: 7/9/2008 5:41:50 PM EDT

[#3]

there's a thread in here somewhere on the DI system and how it works I just ca't remember where I saw it. Anyway it did cover some common and some not so common reasons for FTEs and jamming problems. Sorry I don't know where it is but if you find ,it may help Tacked in troubleshooting forum "how it works" check it out, hope it helps

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