Need Help With a Problem (Or Maybe Not)

AR/M4 AR Technical Discussion
1

I think im having a problem with my BCG retracting behind the ejection port, and therefore causing my brass to hit the back of the ejection port/bottom of the shell deflector.

Im not sure this is even a real problem, thats why im asking here.
I dont think the buffer retainer hole is out of spec because when closing the upper on the lower, the BCG pushes the buffer just sllightly off the retainer like its supposed to.
So that leads me to believe that the receiver extension is too long. If I could thread it one or two more turns it would seem to correct the problem.
Im not sure if I should try to grind the receiver extension in order to shorten it.
I dropped a small plastic disk in the receiver extension as a spacer to test what would happen. I understand this is not a good fix, I just wanted to see what if any effect it would have, and it seems to have done the trick to an extent.

Dented brass

Area of wear on the deflector/back of ejection port. The brass does not touch any other part of the deflector.

Plastic Disk used as a spacer in the receiver extension. I punched the hole in it. Also, it is soft plastic, nothing that could break and jam up in the extension. Again, not any kind of permanent fix.

Before the spacer. I inserted a mag so you can see the bolt catch and see the space between the bolt face and the bolt catch, hard to tell from the angle of the pic, but the bolt face is just behind the port or flush with it.

After adding the spacer you can see that their is less space between the bolt face and the bolt catch.

I know people will say to just leave it alone since it has not caused any malfunctions, but what I want to know is if it is normal or if something is not right/ out of spec.
This is a hobby for me and I dont mind tinkering with something to make it correct.
Or maybe I should try a new receiver extension, this one came with my MOE stock kit.

After watching some slow motion video of AR’s, it seems that the brass stays held on the extractor until the BCG stops, so with mine it just drags the brass into the back of the ejection port, ejecting it at about 2 O’clock with a carbine or H buffer (BCM 16" Middy).
With the spacer it ejects at 3 O’clock

Any thoughts or comments appreciated

2

Normal.

If you have any desire to change how the brass contacts the deflect (which really doesn't matter at all) you have to change how fast the weapon cycles.  But that's only if you are absolutely completely off your rocker neurotic about this one tiny aspect of the AR that has absolutely no bearing on whether it is functioning properly.

Or as Rob would say “just shoot the gun”

3

Why don’t you tell us what TYPE AND MAKE of AR you have. What type of extension, was this a Frankenbuild, etc…

You mention something about the receiver extension. Take a pic and show us so we can see why you think it is too long.

Finally help us to help you. We cannot read minds.

If your only concern is brass hitting the shell deflector like it is supposed to then you may want to sell your AR.

4

Its a BCM 16" Mid length upper with PSA BCG/Lower/LPK and a mil-spec MOE stock kit from PSA
I dont know if the Stock kits come from Magpul or the retailer puts them together (the endplate was OD green like the stock so I assume that was from Magpul at least.

Im trying to find out if it is normal for the BCG to move behind the ejection port like it is. I am wondering the the receiver extension may be out of spec causing that.

You say that the brass is hitting the shell deflector like its supposed to, so its normal for it to only contact the base like in my photos?

Im just trying to find out if its within an acceptable range or if something is not right.
Yes its a little nit-picky, but this site is about the details.

5

Who assembled the lower? Can you take a picture of the area where the buffer retainer pin and lower receiver extension meet up.

Do you have a true carbine extension and is the spring correct?

6

The face of the bolt should go around .250" behind the bolt catch and line up with the rear edge of the ejection port.

Dump that spacer ASAP.

Hitting the rear of the ejection port points to excessive BCG speed, too much extractor tension or too little ejector tension.

Maybe try an H2 buffer.

7

Both of my Colts do not do that but since its a shell deflector who cares. Maybe your over gassed causing a faster blow back or a extractor issue, or a combination of both. Just a guess

8

This. Also see if the buffer spring is in spec (correct length since they shorten with use), and if an O-ring is employed under the extractor (remove it if so, leave the insert in).

9

My BCM 16" middy does the same thing with xm193 and m855. I also have brass marks on the peak of deflector. BCM spring, bcg, and RE. DD lpk. It does it with both H and H2 buffers. Hasn’t caused any problems as long as I’ve had the upper; just over 1k round count.

Reloaders, is dented brass a problem? I’ve been saving my brass for when/if I get into reloading or to try and sell it.

10

Dents like that are no problem at all. if it’s real deep i’d chuck it…
the only thing that tends to really mess a case up for reloading is if the case neck gets kinked in.

11

I wondered how long it would take for this to spread from its point of origin.
Its not uncommon for the carrier to move that far back. As long as it is not going back far enough for the key to hit the lower its not a problem.
Watch the high speed videos on youtube. The fired case leaves the bolt face before the carrier reaches it rearward travel. Others have already mentioned some of the items that determine how soon it starts ejecting.

12

the case starts coming off of the bolt face as soon as the neck of the case clears the neck of the chamber and continues from that point until it’s thrown clear of the bolt when the case mouth clears the front of the ejection port.

13

Does your extractor have an “O” Ring around the eatractor spring?
If so, remove it and retest.
While you are at it, put a drop of lube on the ejector and cycle it in and out a few times.

14

IG, weren’t we laughing about this exact same subject a couple of weeks ago with the bearded guy?

15

Yes, indeed.

16

Nope. It’ll take care of itself when it’s resized. But then again I haven’t come across anything that was really bad. The dents shown shouldnt be a problem.