This is disconcerting....

AR/M4 AR General Discussion
1

Hey,

I posted my concern with headspacing last week and determined that my BCG is LMT and the upper a BCM with BFH barrel.

I had the BCG and dropped it in after I got the upper.

THIS GUN HAS NOT BEEN SHOT YET.

I apologize for the shitty picture. It’s an ancient, rinky dink camera and the auto focus is apparently not working.

Basically, it looks like the lugs from the bolt are marring the chamber/beginning of the barrel. There are 5 specific areas. 4 are visible in the picture.

If this is happening simply from me dropping the bolt once or twice on an empty chamber by accident w/o lowering the bolt slowly, what’s going to happen when that bitch is slamming back and forth at cyclic rate???

I’ve never seen anything like this with any of my guns.

1.Do I need to send this back to BCM and have them fit a BCG to it???

  1. Can I simply buy one of their BCG’s and drop in and consider it good to go?

I don’t think it’s a good idea to shoot this setup.

Chime in.

Thanks all…

2

I’m not an expert but it’s going to be hard for anyone to tell from that pic. Can you get a better shot? What does the bolt look like?

3

It’s honestly going to be quite hard for anyone to troubleshoot this without a better picture. Can you double check that your camera isn’t on manual focus? Do you have a macro setting (the flower)?

You state that 4 of the areas are visible in the photo, but I think they may be visible to you only because you know where to look.

Help us to help you.

4

Please define marring? Is it gouging the receiver extension, actually displacing metal, or is it just a tell tale signs that they have made physical contact like burnishing/polishing? If it is the latter you are good to go.

You said “I’ve never seen anything like this with any of my guns.” So we have an idea of your background, what are your other guns?

5

Can you get us a picture with the flash turned off? Kind of hard to tell from the wash out

6

I took a pic of mine…
BCM upper and BCG purchased at different times. I did not check the headspace. About 500+/- rounds with no issues.

Does it look like this?

.

7

Hard to tell for sure but I think I can make out the marks you are referring. Have you given BCM a call? It Would be a good idea to get a better picture and send it to them as well.

8

Dude bring it by my house. You live like 15-20 minutes from me. I can take a look at it and let you know if it is actually damage or just the two parts wearing together like they are supposed to.

The barrel extension is brand new and the BCG is essentially new to that extension. They are going to wear together as it is metal on metal. I think you might be way overreacting about this whole thing (headspace, marring, etc).

PM me and I will give you my address. I work from home all day long, so I am available any time.

9

Yeah, there’s no metal displacement or actual “marring”. I shouldn’t have used that term. The spots are “polished” or “shiny”. I ran my pinky over them and there’s no burrs or anything…It’s quite clear that it’s the lugs on the bolt are the culprit.

If this is acceptable, shouldn’t these markings be visible around the entire thing and not just the upper part of the barrel? I wonder if the bolt is mating with the barrel fully and evenly.

I’ve got an LMT Defender, a VIS/Noveske N4 build that Grant did, this new BCM and an old Armalite M15A4.

10

See my responses in quote.

11

Ammotech - - Yeah, kinda sorta…Upper part of the barrel…Upper left part of the barrel. Looks like you’ve got the markings in the same general areas.

Bert - - It’s definitely a possibility.

I know I’m overreacting. It’s my nature…I can be a freak about this shit sometimes.

12

In theory the markings should be visible all the way around, but this is a fighting carbine not a benchrest rifle. Shoot it and the parts will break in / mate together.

I think you are good to go.

13

You will always see “polishing” on bolts just like you do on the carrier, etc. There will always be minor mechanical differences between two machined parts. They will wear together, etc. Seriously, don’t sweat it. You are good to go.

14

the pic is not showing on my computer but I would like to see the marks and or damage.
Is there a way that the pic can be reposted or the op should post a better/lighter pic.

15

Bolt lugs look fine…A bit shiny is some places.

My list of AR’s is above…

16

Bert, PM me your number, I’ll give ya a shout this week.

Maybe we can get up for a beer, bullshit and do some shooting.

17

This whole issue wouldn’t worry me typically; however, again, I just thought it a bit weird to see such wear already when not ONE round has been fired through it yet.

18

I would actually be worried if you didn’t see shinny areas on the lugs. shininess is very, very, very, very, very normal.

Read this thread and look at the pics. You will notice the shiny portions on the lugs of the different bolts. All bolts are of top quality.

https://www.m4carbine.net/showthread.php?t=76465

19

When you pull the bolt back and let her slam home (as you should), it is doing the exact same thing as when you shoot it. No difference except you are pulling it back instead of the gas pushing it backwards. When it slams home manually or automatically, the forces are the same. The lugs are going to lock in place and then unlock. This causes friction and those parts and then the parkerizing will wear off slightly.

Have you looks at you other bolts? I bet they show signs of wear as well (assuming you have shot them).

20

Get with Bert, we are all guessing as that image is not usable for diagnosing anything other than bleeding eye sockets.

Seriously, get with Evil Bert.