ok, here we go.
I've been monkeying around with one of my ARs for quite a while now trying to cure a failure to feed issue. first off, the rifle is a Core15 (upper, lower, barrel, buffer tube).
Last month I sent the upper assembly back to Core15 in Florida for them to diagnose the problem. Along with the rifle I sent all of my testing notes and examples of the damaged brass.

They sent me the rifle back with a note saying that they polished the feed ramps, fired 20 rounds and that the rifle functioned properly.

... not the case when I put the lower back on and go shoot.
I get failure to feeds every other round, sometimes every round when using magpul p mags. The rifle functions better with the metal GI mags but I still encounter failure to feeds while using them.

HERE is the kicker:

I also own a stock Colt M4 so today I decided to take both rifles out and start swapping uppers and lowers. Here is what I found after 200 rounds.

Core15 upper on Colt lower = functions properly with both GI mags and magpul mags
Core15 lower on Colt upper= functions properly with both GI mags and magpul mags

Core15 lower on Core15 upper= fail

what the crap is going on here ?    has anyone else gone through this crap or am I just the luckiest sack of shit on the planet ?

yes, something is out of spec. my gut feeling is that both the core15 upper AND lower are out of spec and that when the two of them get together everything gets out of alignment.

Sounds like a bad marriage....

What are you using for ammo?

Should be Lake City M193 or M855 to be a fair test of how the gun was manufactured to function.

The ammo you are using might be slightly low on power/pressure.

Tolerance stacking of mediocre parts.

did you build the lower ? you may need to tighten up the mag catch so that the button is flush with the end of the threaded portion

the mag catch was flush with the button = same problems
i tightened the mag catch so that the threaded portion slightly protruded out from the button = same problems


this is what im getting when the core15 fails to feed. I've tested 50gr .223, 55gr .223, 62gr .556 green tip and a few higher gr hunting loads. it does the same with all of them.



look at these feed ramps.... this is what core15 sent back to me. pretty gnarly right ?





mmm hmm..
but why does this core15 upper function properly with the Colt M4 lower ?




pretty sure that i will never buy anything from core15 again. im not even going to waste my time dealing with them over warrantee issues. just disappointed.
ill go ahead and order a new upper receiver and barrel from bcm or some other company and see what happens.

Before you just throw in the towel...

Just a though but what buffer weight is in the core15?  have you checked the spring?  You might have too much bolt velocity.

It is normally not a good idea to start replacing parts, until you know the parts you are replacing are truly bad.

Does it mis-feed when you hand cycle it?

yep, that is what I got back.

before I sent it to them I double checked the gas block, twice for alignment.
tried two different buffer springs
tried one of those flat wound buffer springs
purchased and experimented with:
carbine buffer
h buffer
spikes t1 buffer, t2 buffer and t3 buffer
swapped bolt carrier groups with, colt bcg, spikes Niboron bcg

... believe me, ive have tried every-fucking-thing. im stumped other than these feed areas. maybe the gas port is too small?? I didn't check that. . but why would it work with the colt lower on it ?
I haven't inspected the buffer tube itself... maybe that's the problem.. but it works on the colt upper..
im not one to bitch and complain; it just bothers me when I cant figure out what the problem is. thought I would post on here to get some ideas 'cause im shit out of them.

I think the best thing to do is let it die and vulture it for usable parts.


edit: wow, I didn't know core15 had its own section on the forum. I used the phone number on their web site first.  this is probably my 5th or 6th post so I really don't know where to find things on this site.
to core15's credit they were easy to deal with on the shipping process and turn around time.

take the spring and buffer set out of the Colt and swap it with the Core15 and see what happens. somebody really outdid themselves on that ramp job

I am a noob too, but not inexperienced at tinkering with stuff.

It LOOKS from that photo, that someone took a polishing wheel too big for the job and polished a section that's unrelated to the "ramp" part in "feed ramp."  Cartridges don't contact where they polished.  They contact further in (where the barrel and the other part meet), and I see no evidence of polishing there.  


The point is, don't give up on polishing the ramp, they didn't do it. So doing it, could still fix the problem.

yup

That is fugley.  They need to issue a return shipping label to have the complete rifle sent back.

In part, Core's warranty states: " If anything is not up to your standard, accuracy included, if anything goes wrong, gets bent, broken, cracked, misaligned, tweaked, snapped or otherwise, simply contact one of our professionals and we will work to make it right. If you are the 5th owner and the rifle has seen 40k+ rounds, it simply….doesn't….matter. We stand behind our products and we take care of our customers. That is our promise and your assurance."  

keep us all up to date on how it goes op

great service

I am not an expert nor a genius, but your ammo pictures look as the bolt is not moving as back as it should, and it is not feeding the ammo properly. You might have plenty of things to check. Too heavy buffer, too strong spring, carrier is loosing preassure somewhere, gas tube dont fits thw carrier properly, etc etc etc. But I am sure there are experts at this forum that will help you better than me. I had a similar situation, and tried what I told you. What it was I cannot tell, but after  cleaning and checking this parts issue was removed. Now the gun works perfectly.

I tried to refrain from commenting, but when I (or any competent gunsmith) "polish" feed ramps you can literally see your reflection in them.  If they aren't stainless they should be cold blued (I use Oxpho Blue) so as to be "professional."



Good on Core15 for stepping up!

I received everything back from core15.
they replaced the barrel and the gas block/ front sight. (thanks!)
they told me that the taper pin holes on my barrel were out of alignment <----------
the buffer tube was loose when I received it so I tightened that up.

I sent them the barreled upper, lower and buffer tube. they put the rifle together and tested 30 rounds through it and it functioned properly after installing new barrel and gas block.

I believe that it did function properly.

I appreciate the effort by core15 but Im still apprehensive about this rig. its just not the one I would grab if I had to fight.
i'll likely just permanently mount one of my scopes on it and run 10 round mags in it.

Thanks for the update.  It isn't very encouraging that they fail to even correctly install/stake the receiver extension.  

They said the taper pin holes on the barrel were out of alignment?   What kind of gas block does it have?    Front sight base?  You said you checked it twice.   Did you actually remove it, taper pins and all?

When you said it was failing to feed....besides the pictures of the damaged ammo you posted what exactly were you seeing as the feeding issue?  Were you getting stoppages during feeding....BCG getting jammed mid travel?  Double feeds?   Single round jams?

You got a new barrel now so perhaps we might never know the real issue.

Did they repaint/refinish the lower in the M4 Feed ramp area where it was buffed?

The problem was ID early on when the upper worked on the Colt lower. The mag is not being held high enough in the Core lower so you're getting bolt override instead of picking the round up by the case head.

have you put some rounds down it since you got it back ? does it function right ? if not I would not pass judgment on it yet and say its going to be a range run only

no, I have not reassembled it yet, however it is sitting on my workbench in all of its wobbly glory waiting for me to find a purpose for it.

no, they did not refinish the lower. it looks the same as the pictures above.

when I get it back together and shoot a few paper plates with it ill report back; but that could be a while.

A friend of mine had the exact same problem with his Core 15. He took it to a gunsmith friend of his, and figured out the problem. The buffer retaining pin was binding on the bolt carrier during operation. I don't recall what the brass looked like on the rounds that failed to feed, but I definitely remember failures to feed with that rifle. Check the carrier and the pin to see if there is any unusual wear. You can also just take the pin itself out and try running the rifle without it to see if that's the issue or not.

1that's interesting about the buffer retainer pin binding up on the bcg. when I first removed the stock buffer from the rifle it was severely damaged (the retainer pin on the buffer was protruding). I found chunks of plastic down in the lower as well as in the buffer tube. the first time I sent the upper back to core15 I also included the stock, mangled buffer for them to examine.


::: update::::

well I put the rifle back together today. like I said before this one is just going to have a scope permanently mounted to it so I went ahead and cut the post off of it.

I put 90 rounds through it using one 30rd GI mag, one 30rd magpul, one 10rd magpul and one 20rd stock colt mag.

zero malfunctions.

it has a spikes tactical buffer spring, carbine buffer, surefire socom muzzle brake/suppressor adaptor, geissele sd-e trigger, spikes nibx bolt and bolt carrier, scope is a Nikon m223 3-9x. the new barrel that core15 installed is a 1:9 which I requested (thanks).
I shoot 55gr .223

pretty damn happy with it now.    

im pretty sure that the problem was the barrel feed ramps and that the gas block taper pin holes on the stock barrel were "off center" which core mentioned over the phone.

like I said before, core15 was fast and easy to work with. I spoke with the same person through the entire process. it took sending the rifle in two times to fix the problem but it got fixed.

now back to life as usual. thanks for all the help everybody!