It is a brand new BCM BCG in a brand new upper.
It is noticeably hard to “charge” with the CH, even with very generous lube. A smell comes from it, that I am pretty sure is from serious friction.
While sliding the BCM in the upper I can hear a high pitched “zippy” noise, I seriously do not know to describe it. Like moving a zipper up and down fast is the best I can describe it.
I know BCM’s are test fired before being shipped, but what could this be? Is it just in need of breaking in?
Do you have a micrometer or caliper to take measurements? This could tell you what if any dimensions are off.
Check for burrs on the guide rails. Had that happen on one of my BCM bolt carriers. It was real rough and scratched the anodizing off of the upper where it was rubbing. Once I cleared it of, problem went away.
I do not.
Upon further testing, it seems to be the upper. The other BCM BCG is also hard to rack.
I was going to test fire tonight or tomorrow, would it be okay to?
I just received two different BCM uppers last month & both had that issue. They were so tight I was sure they wouldn’t work. I put a couple hundred rounds through each and they are nice and smooth now, no worries. Just REALLY tight tolerances.
Oh okay good. I am going to initially test fire, and get the RDS and irons set, at a indoor range tomorrow. Then Saturday I am going to zero for 100 yards.
It gave me pause too, because I could barely pull the charging handle back without using excessive force, but they ran like a champ and smoothed right out. I’m pretty sure yours will too.
I assume you meant “while sliding the BCG in the upper…”? Is it possible your forward assist is lightly dragging on the BCG?
Damn, my bad, I didn’t catch that the first time. Zipper noise isn’t normal, sorry.
Yeah that is what I meant sorry.
Lubricate (I mean sloppy, dripping wet) your bolt in the bolt carrier, and the carrier where the surfaces of the carrier and key ride in the upper.
If the smell is like matches it’s the carrier parkerizing rubbing against the dry anodized surfaces (of the charging handle and inside of the upper and charging handle channel) – the zipper sound comes from the dry carrier and/or key literally dragging across aluminum anodizing like matches against a scratch surface.
The action will smooth out after a few hundred break-in rounds.
Wow, thanks, that must exactly be it!
yea my DD upper and BCG was real tight new when I got it. Shot a few hundred rounds in it and it smoothed out a lot
Some great information here and almost certain to be accurate since both components are new.
Wish mine were tight. all of my BCM uppers are LOOSE!
Check your FA.
I test fired the carbine with the BCG in question and it worked fine for the only 30 rounds I fired. Tomorrow I will zero at 100 yards, also fire at distances, shoot about 2-300 rounds.
The problem, however, is still present even when the BCG and CH are dripping with EWL.
I put my proven and very used Raptor CH and BCM BCG in the new upper and they work fine, so it is not the upper.
I did the reverse and put the new CH- BCM Ambi- and BCG in my older BCM upper, and the same problem occurred. It did not have the same zipper sound in that upper, though it was hard to pull the charging back in it.
Also, with both CH’s- both ambi’s, one new BCM, the other used Raptor- the anodizing is coming off now, hence the smell, on the left side. I pull back with the right handle if that matters. So something with the BCG makes a lot of friction in the uppers, and causes me to put more pressure on the left side of the CH’s which scratches away the anodizing.
Check the inside of your upper rec. for burrs in the CH channel.
Just curious, what has bcm had to say about it?
I am writing them today. Though I do not know if they will get back to me till Monday.
I wanted to wait to make sure the BCG functions before writing.