I have been fighting with a jamming issue that from what I have read is fairly common.  However, most of the posts or comments made never really had a resolution or the source of the problem identified.  Most people either gave up on it and got a new barrel, or modified their feed ramps themselves to correct the issue.

Well, I have found what the underlying problem is (at least in this case) and thought I'd share so others having the same issue might be able to solve their problem.

Chewed up bullets from them diving between the lugs on the barrel extension...pretty much wasted ammo at this point.


Bullets are jammed between the lug cut outs when trying to chamber a round.  Enough force will eventually push them in.


Feed ramps are too steep to allow proper cycling...the manufacturer did not cut the ramps all the way to the back of the lugs, thus increasing their angle.


This barrel on my bushmaster has never had a single issue with feeding or ejecting...the ramps are cut the full depth of the lugs thus decreasing their angle.


I tried this upper on a different lower, with a different BCG and with 3 different types of magazines...the problem followed the barrel no matter what the other hardware was.

Glad you got it figured out


Not wasted, you can still shoot that

How do you know those ramps weren't cut within spec?
All I see here is a visual inspection. Do you have a comparison photo? I am trying to learn here too.


My rainier match barrel put some marks some green tips like that. I got concerned a little. Sht cycled fine.
Learned its totally normal.

I checked every now and them and the marks on the bullet tips are greatly reduced after 100 rounds.

I don't know whether they are in spec or not but when you have feeding issues before ever even firing a shot..something is not right.  I also had to send the barrel back once before already because the headspacing was too tight and wouldn't check properly with the gauges (I had 2 separate shops check it).

So, I pulled the BCG, then the entire lower from my other rifle (that works flawlessly) and started swapping parts to see if I could figure out if it was maybe a bad magazine, or out of spec lower, or spring problem, etc...the problem followed the barrel no matter what it was attached to.

So after doing all that testing, I concluded that whether it is in spec or not in spec...it is a problem.  And it isn't a rare problem.  A quick google search will provide tons of info regarding people having this same problem, chewing up bullets, failure to feed, etc.  Most have contributed it to a bad magazine or alignment issue where the ramps meet the receiver, but in this case it is definitely the barrel extension and the ramps being too steep.

Keep in mind this rifle still has not fired a single shot, is made of all brand new "name brand" parts.

One of the pics if of the problem barrel,  one of the others is of a barrel that has ate every type of ammo imaginable flawlessly.  That my friend is a comparison.

Who manufactured the barrel?

Here are correct looking chambers.
The feed ramp channels are definitely cut differently.

I was feeling chipper and took some reference photos for you. Hope this helps my friend.
Rainier match 7.5 wylde

it seems this may be a Rainier issue: https://www.youtube.com/watch?v=tl2VPhv4Biw&list=UUZkyHDJ-XFuREehZiAp-xsw

My rainier has ZERO issues.
It was a reference of how the chambers are supposed to look.  Take note of that please.

Gotcha, didn't pick up on that...

If you want to completely eliminate the feed ramps cutting grooves into the bullet's jackets, the four top corners of the lugs each feed ramp is between just needs to be rounded. To find out if the corners need any rounding, when charging the weapon, ride the charging handle all the way forward to see if the bullets catch. If they do, take a little material off, then recheck by riding the charging handle. Keep repeating this test cycle until the bullets will feed when riding the charging handle all the way forward; and when the unfired round is cleared from the chamber there are no gouges present.

Before


After

Here is a barrel extension blueprint which instructs to break and blend all sharp edges of feed lips except at intersection; which this intersection I interpret is that rib in the center of the two ramps that separates them.