So first complete build, finished it up and wanted to see if it would cycle rounds before I went to the range. Well it doesn't, the bolt doesnt seem to be picking up rounds from the the magazine or its riding over the rounds, I don't know. The rounds hit the feed ramp and get caught between the bolt lug grooves of the barrel. At least to my eye.

Pulled the upper apart, checked gas tube alignment, checked for proper torque on the barrel nut I've tried about 10 different magazines ranging from brand new out of the wrapper to used and abused, USGI, Pmags, Tango Downs. Tried my BCM and DSG bolts, all with the same problem.

This is my only lower with a standard buffer tube/spring, all the other have LWRC compact stocks and are not SBRed, this is my only SBR lower so I can't swap to a different lower and try it. And I doubt this lower from Rainier, that I've had for 4 years with no problems, is out of spec.

Excuse the iphone pics, its the only camera I have that isn't film.





What do I do? What could I have done wrong?

Weird.  I had a similar problem but it turned out that the BCG was not cycling back into the extension far enough.  There was a small rubber plug in the end of the buffer tube that wouldn't allow the BCG to bottom out.  It was hard to tell.  I pushed the plug out, and then it worked fine.  How that plug got in there, I'll never know.  Brand new buffer tube from PWS.  They said that they had no idea how it got in there

So you say you have a standard buffer and spring and I assume a standard carbine buffer tube.  Make sure that the bolt lugs goes far enough back to clear the end of the round in the magazine.  if that isn't it, I'm at a loss based on your description.

Standard carbine buffer, tube, and spring. Checked to see if there was some sort of plug in the lower that I've had for years, nothing.

Bolt clears the magazine catch, and will hold open when pulled back on an empty mag.

This is the best picture I can get of whats happening. Which if you open in a new tab and zoom, gives you a decent view of it.


Could it be an out of spec barrel? Its a brand new Ballistic Advantage.

I pulled the upper completely apart, and didnt see anything that looked out of place to me at least. On the upper, feed ramps, or barrel.

If you have another barrel, I'd try swapping it out just to rule out the barrel/barrel extension/feed ramps...  Definitely a strange issue...

Is the bullet tip deformed?  Looks like the bullet tip is hitting a lip in the chamber.  Or maybe its catching on the sharp edges of the feed ramp and locking lugs.  Seems to be alot of brass shavings in that upper.  Also are u riding the charging handle home or are u using the bolt release to send the bcg home?   It looks like u are pretty familiar with the ar15 platform but i had to ask.  Maybe its time to build a pistol lower

It is either a upper m4 feed ramp issue or a barrel issue. If it's a BA barrel issue, they will make it right. What upper is it in?

Out of curiosity, what ammo is that?

And your pics only show it happening when feeding from the right position in the mag, does it also happen when feeding from the left?

Tips of the bullets are definitely deformed, scrapes, gouges, and the like; the brass shavings are from just that. Not riding the charging handle home either, dropping the bolt from the bolt release or pulling the charging handle all the way back and letting go makes no difference.

I don't remember where the upper is from, I bought it a long while ago. I do remember it was from a reputable site sponsor here. Time to find out where I bought it and shoot BA an email.


It happens on both left and right sides of the mag, pictures just show up better on the right.

And for ammo, LC M193, M855, some Eastern Europe SS109, Wolf Gold, and Wolf steel cased. I've tried everything I can think of, even swapped to a different rail/barrel nut.

Have you tried a different magazine, or BCG ?

This looks similar to an issue that I had/have with my first AR build. The rifle will run M855 just fine, but any hollow points and some soft tips would get hung up right after the feed ramps. I would also get excessive chafing and dented cases, along with some rounds having their projectiles pushed further back into the case due to impact. Life got in the way and I never really found a solution, so for now I only shoot FMJs out of it.

But more importantly, is that a gas piston system you have? The rifle that gave me the trouble has an Adams Arms piston system.

What about the brass case is the lip all jacked up?  Is it catching on the case or just the bullet?