Does anyone here have much experience filing down M4 feedramp cuts? This is my first Custom Build, in which I’m using a VLTOR MUR Billet upper (with pre-existing feedramp cuts) and a Kotonics KT68 bbl with M4 cuts.
Of course, the problem (if you can call it that?) is that the VLTOR MUR’s cuts, are slightly LOWER, than the cuts in the bbl extension.
SO, I’m thinking of filing them down with a 1/4" round, SMOOTH cut file.
However, the only files I found locally, were the Nicholson files, and the teeth on the file don’t even start until about 5/8" from the tip of the file.
The problem that arises from the teeth not being cut all the way out on the TIP of the file, is that I cannot even get a stroke of the file accomplished, without the file hitting the top of the bbl extension/lug recess area. This basically means I don’t even have the room for a stroke of the file, and EVEN IF I did, I would probably mar up the top of the bbl extension.
I suppose I COULD use a cutoff wheel, and cut the tip of the file off, and then I would have teeth on the END of the file, where they are needed most. It sure is a pain in the ass to cut a file off though. I’ve been down that road before.
I really hate to resort to a dremel, for two reasons. One being there is not even half the control that a hand file gives, and the second reason is that I’ve never found a Dremel/Foredom attachment worth a damn for making cuts like this. (This is basically MILLING, and Dremels suck for milling). I’ve never had luck with those cylindrical/cone shaped stones.
What does everyone do in this case? I’m not even sure if the tip of each round is even going to impact below the joint between the upper and the bbl extension, but I’m ASSUMING they probably won’t. I could be wrong though.
I’m just not sure.
Does anyone here just leave it alone, and not mess with it? IF this is going to be a necessary task, then I’d like to do it now, while I’ve got the bbl off, and seperate from the upper.
What do you experienced custom build guys do in this case? I’m sure it happens more times than not, eh? (or am I wrong in this assumption)?
I’m not trying to create work, or problems here, so if this isn’t even necessary, then I might skip the step entirely. As I said though, it sure would be nice to get it over with now, if it will be needed down the road.
Not to mention it sure would give me peace of mind, knowing there is a SMOOTH transition between the upper and bbl extension ramp cuts.
What say guys?
i say it is a NON issue, and do not mess with it.
Shoot it first.
will the upper hand cycle and feed rounds?? if so, take it out and shoot it.
dollars to donuts, NON issue.
DONT FUCK WITH IT.
The AR is not a 1911…
Is there something already wrong with the gun?
Nothing wrong with it. It’s not even a complete firearm yet.
It’s a custom build I’m doing as we speak.
Many builders I know, will do this FIRST, before they put the gun together, as it kind of makes sense, to have a SMOOTH transition between the two cuts.
I mean, after all, if the bottom VLTOR cuts are LOWER than the bbl extension cuts, then what’s the point of having cuts in down into the VLTOR upper anyway?
I really think that even though it may not be necessary for the gun to run properly, that it SHOULD be a smooth transition.
However, I’m open to opinions/facts about this issue, and always like to hear from others first. I value greatly, the opinions of others who have been here more times than I.
My knee jerk is, dont mess with it. But some pics would be nice just to ensure that all are on the same page
I assure you I have no way of posting pics that would show the offset between the feedramps in the VLTOR MUR upper, and the bbl extension.
Even if I had a camera that was capable of doing it, I doubt I would be capable of it. I never have been able to take up close detailed pics to show detail.
I am guilty of throwing all my money towards guns, and not cameras.
I can understand pics are cool, but I don’t think they are really needed in this case are they? I think everyone understands exactly what the situation is here, correct?
Thanks to all.
need pics - not sure what you mean by ‘lower’. does the barrel extension overhang the vltor ramps? (as in a non M4 ramped barrel and M4 ramped receiver)
Nothing like that feeling of justified:D
I think I understand what you are saying and in that case I would file them down as a bullet tip could get hung up in the overhang of the barrel extension. But that is just what I personally would do.
I think I understand what you are saying too, but I don’t think you have mentioned how significant the difference is. Is it possible to quantify the amount with a depth gauge or feeler gauge or something? That might help others more knowledgable than myself to form a more educated opinion.
Just a thought…
My completely uneducated opinion is that I would personally want a fairly smooth transition between the receiver raceway and the barrel extension raceway. There appears to normally be enough friction here to impart some copper from the jacket to the ramp, so I would assume that too rough a spot might cause a feed stoppage of some sort.
But my opinion and a $1.25 MIGHT get you a cup of bad coffee.
-RD62
If the MUR’s cuts end lower than the barrel extension cuts begin, you will have feeding problems. I had this exact issue with a Spike’s Tactical lower and a Ko-tonics barrel, and the combination would not even hand cycle a full mag (don’t worry, I was using dummy handloads with no powder or primers); bullets would hang on the barrel extension and cause setback.
If you really want this combination to work, you’re going to end up filing down the barrel extension to match your upper’s extended feed ramps. This is definitely possible, but realize that your barrel will then be forever tied to this specific upper (unless your next upper has the exact same feed ramp profile).
Does the side view of your problem look something like this?
Yes, that’s the exact issue I have described to the T.
I will make sure they get filed down, as soon as the correct file is acquired. As stated before, I cannot make a typical round smooth cut file work, as the teeth of the file START (or end) about 5/8" from the tip of the file.
SO, this won’t allow me to even get a partial stroke of the file, without the tip of the file hitting the top of the bbl extension.
IOW’s, I need a file that has teeth cut all the way to the tip of the file.
Thanks.
Paul C
One of the parts was manufactured out of spec.
Replace it and move on.
y’know - i’ve yet to see the spec for M4 feedramps. not all manufacturers have the spec, and some reverse-engineer the depth by looking at the colt barrels. i’ve seen them vary across the board quite a bit, and i’ve had to ‘correct’ a couple of barrels to match receivers when i encountered the same issue (mostly stainless barrels).
i’d recommend you send it to a gunsmith, but i did it myself with a 3/16" dia aluminum oxide dremel grinding stone. i clamped the barrel without the receiver such that the angle was correct if i held the dremel horizontal. i would slide the receiver on frequently and check the progress of the cuts, making any small changes if needed. when i was satisfied, i used a craytex bit (rubber) to break all bottom sharp corners around the ramps on the extension lugs, then followed up with a felt polishing bit and metal polish.
I did the same thing with a stone bit on a 1/8 shank (didn’t wanna say dremel) and once it was finished I used a rubber bob that is an abrasive to polish it out.the ramps look like glass and the angles between the 2 match for a smooth transition.
this would be the best "do it yourself " way. or have it milled by a machinist/gunsmith.
but it is easy to do yourself with an air pencil die grinder and 1/8 shank bits or a dremel tool.dremels have a bad reputation but the problem is the operator not the tool.
this is one after polishing with the first grit.
Nice work man:cool:
Abraxas,
I’m assuming this “stone bit” you mention, is one of those cylindrical/cone shaped stones?
I’m thinking that an Aluminum Oxide shaped tool like that would work best. Stones obviously can work, but the ALOX will just promote less chatter, and work better. Either way will work I presume.
Thanks for posting.
On a seperate note, does anyone know WHO produces MILSPEC barrel extensions, OTHER than Colt?
I don’t suppose there are any manufacturers producing a MILSPEC 6.8 barrel extension is there?
I spoke with someone today, who knows quite a bit about AR’s, and who is very well known and respected in the industry. He told me that Colt produces Milspec bbl extensions, based on the “original blueprint design” (his words verbatum).
So he basically said that I would NOT have had this problem with my M4 feedramp cuts IF I had used a Colt bbl. (or at least a Colt bbl extension.)
However, with this being a 6.8 midlength build, that wasn’t possible.
I’d also like to know if anyone can tell me how a bbl extension installs onto a bbl? HOW is the bbl extension attached to the bbl blank? I mean, can I buy a Colt 5.56 bbl extension, and have it fitted to a Noveske bbl, or some other quality bbl? ( I was also told that even Noveske is using bbl extensions that are not in spec with Colts bbl extensions). This of course, I have NOT confirmed personally.
I’m trying to determine if I have ANY other option(s) for a Milspec bbl extension on a 16" Midlength gas system bbl. Now this WAS supposed to be a 6.8 build, but I might decide to just stick with 5.56, IF I can find a midlength bbl with a Milspec bbl extension that will work.
Of course, as a last resort, I will buy the proper rotary tool attachment and grind/mill down the M4 feedramp extensions myself. As I have said though, I would really prefer to just buy a bbl/bbl extension combo that will work without milling the feedramps again. I know it’s not that tedious of a task, but honestly, curiousity has got the best of me, and I’m really wondering if this whole Colt Milspec Barrel Extension “Myth” is true?
Can anyone confirm? Thanks guys.
the extension is screwed on and held with the pin that indexes into the upper.
there is a tool used to screw it in place that fits into it, like a socket onto a bolt.
I think JP sells extensions but the tool …?
I know two induviduals who had similar old style Colt rifles, both did not have M4 feed ramps. Both of my pals took them to classes, worked them out in the field ,qual’d with them, etc. etc. They both never had an issue that could be traced back to a “feed ramp problem” When it came time for a another friend to purchase a Colt govt carbine that was NIB but old. He asked what should he purchase or do to it so it was reliable, he was not an AR guy. We all joined in that it should run fine as is, it did and it had no M4 feed ramps. My experiences are pretty much the same. My point is that , M4 ramps were designed for the military for full auto use and pretty much thats it. I will join the chorus of individuals who say leave it be, buy more good mags and ammo and get some quality training. Leave the Dremel for other things…