New upper assembly, barrel extension fits nicely in the receiver at the top and feed ramps flush with the receiver. The center section of the extension protrudes into the receiver a bit (it looks worse than it is in the picture). Do I have a problem on my hands? Recommended fixes? I would like to hear from Dano and Sully as well as anyone else. Thank you all.

From the angle of your photo it looks like a M4 extension in a rifle upper receiver. Does the bolt fully close on your ammo? Does it eject easily without being fired?

Hi,
Yes, M4 ramps/rifle receiver, bolt closes good, headspace is good. Unfired new upper. I'll simulate/check extraction with snap caps. I'm going to check alignment with a laser bore sight also. Thanks for your reply.

Please delete.

It's supposed to.

You have a steel bolt and carrier careening toward your barrel, at around 20 mph, what would you rather have it hit to stop it - a steel barrel extension, or an aluminum upper?

Does the pivot pin lug have a seam in it?

I have heard both sides on this issue, and never got a definitive answer.
This side says BE should protrude slightly.
That side says nay.

I will tell you this, out of the 6 that I have, 2 are flush and the rest are recessed ever so slightly. Maybe 0.001"-0.003".

Truing or lapping the receiver face is a possible remedy, though I have never screwed with it.

No.........doing this will actually allow the barrel extension to seat deeper in the upper causing even more protrusion.

If it feeds and functions reliably I wouldn't worry about it. If it doesn't you're going to need to contact your upper receiver source or the barrel manufacturer. I've heard that a lot of funny (funny bad not funny ha ha) barrel extensions have been hitting the market lately. Perhaps your barrel maker sourced some of them and that's the source of your problem.

Thank you all for your assistance.
I meant the picture makes it look worse than it is. It appears to protrude more in that 1 photo. I will get a couple more pictures up no problem. Yes, it is a polymer upper receiver.

Shit. Not thinking. You are correct, my suggestion will only amplify your issue,  OP.
DISREGARD.

A couple more pics:

Thank you for your replies. All the posts are useful to me and I appreciate it. The solution I'm going to go with is replace the upper. Have a great day everyone. -CB

Well guys, what I have done seems to have fixed this.  My Daniel Defense 556 had this same problem.  My receiver was made with the M4 as well as the barrel.  So I saw this problem and was able to fix it with a couple of barrel nut shims.  I think I had to use a 1 and a 2.  My barrel protruded in the receiver just like your picture.  In my mind if the tip of the bullet would catch this edge when going into battery you could run into a jam, or a stovepipe and who knows what else?  The barrel and the receiver m4 should match perfectly.  There should be no edge or lip for the bullet to come into contact with.  The shims will work on the opposite side of the barrel ring.  You have to snip about 1/8 of an inch out of the shim to fit the pin in the barrel.  You may have to experiment with the quantity of shims to get your receiver and barrel to arrive at a complete match.  But not hard to do.  My rifle was a complete unit from the manufacture.  In my opinion the receiver was cut to short or who knows the barrel was cut to long, and the barrel is Hammer Forged.  So bottom line I think its a receiver problem.  But its quite easy to see from the picture something is not right.  But in my mind its no big deal and quite easy to fix.  Also this fix will not effect head space in the least.  Also there is no way the bolt can hit the receiver.  So when building an AR just be aware of this and check how your barrel and receiver match up.  The shims can be purchased at Brownels. Im a little shaken that my manufacture did not catch this, but thats quality control, and some of that is lacking these days. I would be interested in other comments.

Hi Joewales, I too check the parts fit and function carefully on all my builds. A point I come across often is lessons I've learned that as a person that assembles my own (I'm not an armorer or gunsmith) is that "not all parts work in all rifles." I remember one build I went through several uppers to get a satisfactory fit and finish for various reasons. I thought the same thing you did about this upper/extension fit that it would likely cause malfunctions. I think the upper receiver in this case is not quite square due to the fit around the circumference of the extension. I did take a picture of ramp area with a loaded magazine inserted to see how it lined up. I was surprised the top round was aimed right at the middle of the feedramp. The rounds in a loaded mag sit much higher in relationship to the ramps than I thought. It's possible it could have run with no problem, but I don't take chances. It's either a correct fit or it's not. If it's not I'll fix it. The line up/fit was obviously not correct to me. I'm not going to try to repair the upper or make it work. Its being replaced. As for shimming it I wouldn't do that personally. That shortens the distance that the extension goes into the receiver and I'm just not comfortable changing standard/regular dimensions on firearms it's a bit of a red flag to me that something's off and I could be making a mistake so I have to find a fix to make things go together normally which many times is parts replacement. The funny thing is many times a removed or discarded part for one build part will work fine in another. That's just the way it goes. It's was hard to photo through the port door but here it is, sitting much better than I thought. Thanks for your input, appreciated. -CB

Yeah, I agree with most of what you say.  I went over to Brownell's today (I don't live far from their warehouse and store is located).  I had to pick up another Barrel assembly and receiver for another build I'm doing.  I checked the m4 ramps on the new receiver and the new barrel and they matched perfectly.  I talked with a gunsmith friend of mine in Omaha and told him what I found with my Daniel Defense.  He said he had not seen the problem.  But after talking with him and explaining and he understanding the problem.  He feels that the receiver was just machined a few thousands short where the barrel ring and the receiver mount up.  He felt by taking the ridge out of the feed ramps by shims would cause no ill effects.  I have three other 556 nato rifles and the feed ramps match up perfectly.  He said the feed ramp is extended into the receiver because larger grain bullets when its started going forward to battery the tip hits about center of the barrel ramps but as the bullet tapers back sometimes you need the extra ramp space the receiver provides.  But oh well it is an opinionated subject.  Before I was getting a jam about every 30 to 40 rounds.  I have run about 500 rounds with this fix and no jams so far.  I have had the rifle a little over a year now.  So to each their thoughts about the subject.  And again Im a little disenchanted with Daniel Defense for their quality of inspection.  Daniel Defense is not a low priced weapon.  And when I looked at the exact same model at Brownells today the m4 ramps were perfect.  So go figure I get the defective junk? LOL .  Thank you it was nice exchanging thoughts.  And from now on I'm going to check if I buy parts to build a AR or purchase a complete uint.

Cb, I was studying your picture again and I can't really tell?  Is the M4 ramp cut into your receiver?  All of mine are?  Just food for thought.

Hi Joewales,
The upper I had a problem with didn't have M4 ramps.
Thanks for the gunsmith info much appreciated. Did you take your fresh build lower to match up to the new upper? Maybe I'm just lucky I have found not all uppers fit all lowers. It's great your feedramps line up correctly that's part of the correct fit. It will also have to line up correctly side to side, front to back and up and down (the upper receiver to lower receiver fit). Maybe I'm a little picky but when you're looking for it the various fits start to stand out. A good fit is beautiful! We can chat and discuss anytime. Thanks for thinking of me. Best to you. -CB

ETA: I haven't had this problem before of the extension protruding into the receiver. I couldn't say for certain exactly why it occurred. That's why I asked. I have since checked five other builds they all look good/flush. This hobby comes up with new things to learn all the time. I have photos of some other line up and fit issues I mentioned I'll look for those it will take time.

CB

Sorry I did not answer your last post.  I got busy with a new build (223 Wylde) and forgot.  

On the last two builds I have been using the Noreen lowers and no problems with match up.  

I went back to your first picture and see what you mean the extension protrudes into the receiver.  Looks like the extension is flush with the receiver at the top and at the middle and lower part of the extension it’s protruding.  I went back to my gunsmith and showed him your picture.  This is his opinion.  As you say the extension fits tight, (he calls this a tight slip fit as it should be).  He feels the hole on the receiver was not machined correctly and not bored correctly on centerline of the receiver.   In his views there is really nothing you can do but replace the receiver.  I do agree with him.

How ever with my Daniel Defense the extension protruded evenly all the way around, top, sides, and ramps.  My receiver was just cut to short.  The shims I use spaced the extension so it was flush to the receiver (no ridge).  I have run about 500 rounds through this unit and it’s running smooth as silk.  Thanks again for bringing this to view.

Hi Joe,
Don't worry about timely replies we all have our lives to live. You hit the nail on the head. The extension was flush at the top and protruding on the bottom. As if the barrel was pointed down slightly. I too was working with a gunsmith on that build. I felt that upper build was unsafe.  The bolt trying to lock up in the extension would not be straight and square with the extension and I wasn't going to let that go. My kids shoot these. I did junk the polymer upper it's a bad apple. Sometimes these things happen. I screwed up the day I bought that thing, it doesn't have M4 ramps and my extension does DOH! Yep, I screwed up. Aside from that, that poly upper was a problem and a lemon from the minute I got it. I replaced it with an aluminum upper and everything fit together beautifully with no problems. I shot that upper a couple days ago it ran like clockwork -0- malfunctions.  thanks for the input, info and opinions, it is appreciated. Have a great day. -CB

ETA: I do have some additional info and photos of what works well for me and what doesn't when selecting an upper receiver.  I just haven't posted it yet.
Funny enough, when I replaced the polymer upper with an aluminum receiver I purchased 2 new aluminum stripped uppers, one for a different build. The one I used first has an acceptable fit and finish. The second one has an ugly side to side fit on all my lower receivers. I wouldn't purchase these specific parts if I was making the purchase in person (although it could happen) I do make most of my parts purchases by mail order. The poor fit happens to all the manufacturers the problem is not cheap parts. It's just slight differences in the machine work. I'll try to get a useful post on selecting your uppers and lowers for a good fit done promptly.

With new upper, fits nicely:

CB

You are absolutely correct about the lockup of the bolt and barrel.  I again was talking with my Gunsmith and he mention this.  CB you have this down to a fine art.    I agree with everything you have said.  I like you pay attention to detail.  Always something to learn when building AR's.  Im starting a build on an AR10, but not sure on the caliber yet.  Its nice to communicate with someone that knows whats happening.  Thanks again for the post, and I have learned a few things.

Joe