Problem with AR feed ramps...please help

[Touchdown456]

Hello all,

Well I feel like an idiot. I was sick of ejecting an unfired round and always seeing scratches/grooves carved into the head of each and every bullet. I've broached this subject many years ago on calguns and was led to believe that it was most likely burs on the feed ramps that were scratching the bullets. So last night I decided to get out my little Arkansas stone set and lightly try and remove some sharp edges on the ramps. Well, I guess I went a little too far, because now when I close the bolt, the tip of the bullet jams in the gap between the lugs on the barrel extension (at the top of the feed ramp). I can cycle the bolt by hand and it will dislodge the bullet, but sometimes the force of the initial impact has been actually pushing the bullets INTO the cartridges!!

So, my thoughts are that I removed just a bit too much material (although I thought I barely removed anything), and now as the tip of the bullet moves up the feed ramp, it falls into the gap between the lugs early and jams.

Now, my question is - am I screwed? Is there any way to fix this by myself? If not, can I have the barrel extension replaced? Or do I need an entirely new barrel? I feel like an idiot because usually I don't just start messing with stuff before I attempt a fix, but last night I was just so frustrated that I just jumped on it.

Oh well
Thanks

[Gutz]

I think you are screwed and need a new barrel. Pics would help A LOT!!!

[Touchdown456]

Yeah I'll post some pics tonight when I get home from work. I just can't believe I didn't look into this before I started otherwise I probably would have learned how tight the tolerances are on that piece.

[ar15barrels]

can I have the barrel extension replaced?

Not easily.
There is no standard for timing.
The extension sets the timing of the barrel.
If you swap extensions, the top of the barrel changes.
That screws with the gas port, the markings and the FSB if it has one.

[Touchdown456]

Here's some pics... I'm so shocked cause it doesn't look any different than it did before I started. (the links are safe, they are just links to my dropbox)

http://db.tt/P3zCKgSm

http://db.tt/tArwb5mM

But, if I am screwed, which it seems like I am, anyone know who has 7.5" pistol barrels in stock?

[kcstott]

If you used a hard Arkansas stone I find it hard to believe your could have removed to much material. It would take quite a long time if stoning to removing even a thousandth or two.

I'd look at your magazine feed lips

[Hoagiem]

IMG_20130327_013429 edit.jpg

Carefully

[ar15barrels]

I was sick of ejecting an unfired round and always seeing scratches/grooves carved into the head of each and every bullet.

You should see what the bullet looks like after going down the barrel and impacting a target...

when I close the bolt, the tip of the bullet jams in the gap between the lugs on the barrel extension.

Don't "test" the feeding on the bench.
Test the feeding at the range via live fire...

If the first round is failing to chamber, down-load the magazines by one round as the last round is probably too tight.
Also, the chamber should only be charged by locking the bolt to the rear with the bolt catch, returning the charging handle forward into the receiver, inserting a loaded magazine and then depressing the bolt release.

If you insert a loaded magazine and then rip the charging handle to the rear and release the charging handle to load a cartridge, the charging handle bounces up and down as its going forward and that bouncing eats up energy in the bolt that would have otherwise been used to strip the cartridge.
With the lack of energy, it is common to not completely chamber.

[Touchdown456]

If the first round is failing to chamber, down-load the magazines by one round as the last round is probably too tight.
Also, the chamber should only be charged by locking the bolt to the rear with the bolt catch, returning the charging handle forward into the receiver, inserting a loaded magazine and then depressing the bolt release.

It unfortunately was happening with multiple rounds throughout the mag, not just the first or tightest ones.

And yes, I was depressing the bolt release in order to chamber.

I know it was whatever I did because it was running perfectly before my little "fix it" stunt.

[Touchdown456]

Carefully

Thanks for the illustration. I'll give it a shot, hell I can't screw it up worse than I already have.

[Intimid8tor]

I know it was whatever I did because it was running perfectly before my little "fix it" stunt.

Well now you know that scratches on the tip of a bullet were worth a $200 barrel.

[Touchdown456]

Well now you know that scratches on the tip of a bullet were worth a $200 barrel.

Haaa, yup. And it's those life lessons I hate the most.

[ciscosixgun]

You also need to make sure you have enough jump between the feed ramps. The ramps on the barrel extension need to be set back slightly from the ramps on the receiver and not overlapping the receiver ramps. It's hard to tell from your picture if that's the case.

This involves removing the barrel and ramping the extension a little more so you have about 10 or 15 thousandths between the two feed ramps when you put the barrel back in and tighten up the nut.

[skohl]

Feeding Problem

The description of your feeding problem is exactly the same problem I have with my DPMS 308. I sent it back to the factory a couple of weeks ago as it is under warranty. They said 4 - 6 weeks. I'll post their diagnosis / fix when I hear from them.

[sarge1572]

I don't mean to nitpick, but your original post said you thought you had problems with the feed ramp, and you STONED the feed ramp, but your pictures are of the locking lugs, and neither one shows the feed ramp.

often the "marks" on the shell are nothing more then the sharp edges of the magazine leaving tell tale marks as the round is pushed from the mag to the chamber. Can you take a pic or two of the open bolt, mag inserted, with the feed ramp in focus, and a couple of rounds, it doesn't matter if they're fired or not, showing the "marks" you're concerned with?

Not an expert, but I do maintain and repair 100 of these.