Ok fellas the story goes like this.  Ordered a stripped upper with M4 feed ramps...thought I was getting a barrel with m4 extension but ended up getting a barrel without it.   Now after putting 100 rounds through it at the range it failed to feed by hitting the exposed gap (Copper in the gap) about 7 times which is enough to piss me off.   SO the question is what is the best procedure for dremeling these ramps into the extension.  I read the m4 ramp faq but that mostly dealt with putting them into the upper and not the extension.   A little guidance or warning would be very much appreciated.  

I think I would have to give you a little of the warning than I can of the guidance...

Uppers are $100 pieces of aluminum.  Barrels and extensions are $200+ pieces of steel.  That right there is the reason you don't hear of doing the opposite of what you are looking to do.  

I take it you barreled your own upper so I'd say as much as it might not be what you want to hear, try and trade your ramped upper for a non-ramped upper.  I think it's your best bet if you haven't done anything permanent to your upper.  You might be able to find someone in the EE want ads seeking an M4 ramped upper.  I'd start there and maybe just sell it outright and then buy the correct one.  

I would remove the barrel before I dremeled, but you'd want to be able to constantly check to see whether you are there yet.  Probably not a bid deal.  I can only assume you installed the barrel yourself.  

I got my upper from ADCO and there was a little edge between the custom barrel and upper and Steve used a jewelers file to touch it up, but that is steve...

You need a mill and a carbide cutter.

With the barrel in the upper, scribe the exsposed ramp lips against the upper receiver cuts.

Now jig'g the barrel, with the new cut angle to be just past the scribe lines at the begining of the barrel extension, to the center of bore (111.5 low(half the bullet diameter))  You are not just deepening the begining of feed ramps, but the beginning angle back threw the exsisting angle with the end result being that the bullet tip guided up the ramp will end with the bullet being feed center of chamber.

Again, free handing these cuts with a dremil is not the way to go since a screwed up angle or widened ramps  will not longer feed the round truely center of the chamber (read bounced off the side/top of the chamber bending/off axising the bullet tip in the case).

just do it, it's not like your trying to reshape the locking lugs or something.  


i had the exact same thing with my bushmaster barrel and M4 upper.  i didn't take the barrel off the upper or anything.  in fact it would be easier to get a perfect match without removing the barrel.  just hit it with a fine grit dremmel grinding tip.  i used the cone shaped one and it seemed to work really well.  i ground on the barrel extention at a consistant angle until the 2 ramps looked like they were continuous.  it actually takes more grinding than you would think since the extention is pretty hard.  then i polished it with some fine grit diamond paste.  i can scrape on it with a dental pick and not even feel the seam between the two.

hell, it's so simple a monkey could do it.

i've put about 1200 rounds through it since then without a single problem.

well grizzlyarms, I was sure that at least one person out there had tried it and succeeded without any problems and I guess you are the one.  I'd bet you are an exception and still wouldn't recommend it.  

What is your background in rifles?  I can only assume this was something you didn't have to think twice about since you accomplished your goal when there are dozens and dozens who don't.  I'm not knocking you or giving you a hard time, I'm acknowledging that you are the small percentage of AR hobbyists who could perform this.  Wait, is grizzlyarms a company?  That's not fair, you are a gunsmith, aren't you?

So you really think he's got a 90% or better shot at getting this right with a dremel freehand?

Quoted: So you really think he's got a 90% or better shot at getting this right with a dremel freehand?

Getting the round to feed into the chamber, and not get caught on the extension feed lip, I'll give him a 90% chance of getting that corrected.  

Getting the feed ramp angle correct and the bullet tip not dancing off the sides of the chamber during loading and causing increased group size? Free handing cuts with a dremil, and I give him a 90% chance of getting the angles wrong, or ever worse, bouncing the dremil and causing more problems, I would rate that as even higher.

Simple put, I have seen home made dremil jigs/deveices that allow even 80% 1911 frames to be finished.  The point that I still need to make is the angles need to be correct, and free hand cutting is going to end up with the wrong end resolts.  If nothing else, send the barrel off to Kurt to have the M-4 feed ramps cut.  A few dollars spent on having the ramps cut correcty will be well advised, verses cutting them wrong and having a barrel that just sprays (read greater than 3 MOA).

Send the upper back and exchange it for a non M4 upper . Les your dead set on the M4 ramps .

Thanks for the help guys.   I did barrel this myself.   What do you guys think about just somehow filling in the feed ramp gaps with something  (maybe jb weld???)?  I am not dead set on feed ramps I just got a good deal on a non ramped barrel.

I hac the same exact problem with my 11.5 Bushy on a colt M4 upper.  The dremel technique with a super fine, cone shaped bit. It was so easy I couldn't beleive it.   I did take the barrel off and only ground small amounts at a time before checking it against the upper.  There is definately something to say about the angles and not widening the "ramps".  As far as the groups go I haven't noticed any changes.  Still puts three rounds in the same hole at 30 yards (Dept. ranges have their limitations).  This is strictly an entry gun for CQB so the long range guys probably know way more than me..  I have 1000 rounds with it so far and not a FTF.     Good luck