I'm having a slight problem with my CMT M4 upper (m4 feedramps). It seems that when I chamber a round, the feedramps make a slash on the bullet. Will/can this cause accuracy problems and should this be fixed? Its a Mk12 clone so I'm all about accuracy.

Thanks

It's probably not the feedramps but a sharp edge in one of the barrel extension lugs.

You are not the first operator to note this problem on this site.  It seems not be corelated to any particular rigs.  First, we must assume you are playing with your ammo (running through unfired rounds to see this effect).  Some folks never see this because they fire every round that is chambered.   Also, it would be interesting to see some photos of the gouges in your bullets.  

The culprit has at times been the magazine, not the chutes.  I assume you find copper gilding residue on the chutes, not the mag.

I also have questions about the effect on accuracy, but with the round spinnng around  200,000 rpm coming out of the barrel, it may be negligible.  There can be  at least two things involved: 1)asymmetric CG shift radial and lateral, and 2)asymmetric aerodynamics.

I think it would be a good write up for the site to have some bench rest operators take a rat tail file and camera to the range some day with some match FMJ and document the accuracy effect.   I am a relatively new member, so this may have been done already.  

It would also be interesting to see the difference between letting the charging handle go vs. actually firing a round.  

It seems pretty normal, but I've only noticed it when cycling ammo using the charging handle. Which is normally the only time you hava chance to notice it.

Next time I'm shooting, I'm going to eject a few rounds after firing and inspect the bullet.

I carefully file off any burrs on my bullets for maximum accuracy.
I saw this in a movie once.

I too, have noticed this. I'm curious to know what it does to accuracy. Not like I'm a good shot anyways.......

C'mon guys, it dosen't do anything to the bullet otherwise it wouldn't be winning those shoots at Camp Perry.

Quoted: C'mon guys, it dosen't do anything to the bullet otherwise it wouldn't be winning those shoots at Camp Perry.

He might be on to something.  I'm no Camp Perry champion, but I can clean the 200 and 300 yard rapid fire targets and my upper does scratch the bullets when the feed from the mag.

I have noticed bullets getting scratched when ejected from my Stag upper as well... but are they really being scratched when ejected or chambered? If they get scratched by chambering, ther really wouldn't be anyway to tell is it has been scratched without disassembly to ensure that its not just caused by the unfired round being extracted. The ejector could just be tilting the bullet into the chamber lugs on extraction.

Quoted: The ejector could just be tilting the bullet into the chamber lugs on extraction.

Good point.  That's a possible explanation that had not occured to me.  That may be why I don't see accuracy degrading.

Quoted: I carefully file off any burrs on my bullets for maximum accuracy. I saw this in a movie once. Now that's funnyhr

CMT uppers have M4 feedramps...?

Quoted: I carefully file off any burrs on my bullets for maximum accuracy. I saw this in a movie once.

Sniper?

Quoted: CMT uppers have M4 feedramps...?

yes they do if you want them

Quoted: CMT uppers have M4 feedramps...?

No

Quoted: Quoted: CMT uppers have M4 feedramps...? No

I was about to say.  Somebody stole my M4 feed ramps then

You can get CMTuppers with or without M4 feedramps.

Burr? has to be?

If its new shoot it more!

The Bullet should not have a scratch on it when you eject a unfired round!
Brass /Case ?

Just in case anyone cares...  here is what this thread is about.



Caused by the bullet hitting the sharp edge of the barrel lugs on the way into the chamber.

Once when I was polishing up some ramps, I made an effort to knock the sharp edge off of the lugs and it really did help to lessen the size an depth of the cuts.

Exactly....  and thanks for returning us to topic. thanegrooms.

The curve in the scratch would indicate that it's being done while the cartridge is being pushed forward and UP by the bolt, from it's position slightly below bore axis when in the mag and being aligned with the bore as it enters the throat.

Any scratches caused by extraction would tend to be straight as the empty cartridge (or in this case with the bullet still intact) is pulled straight back by the extraction part of the cycle and then ejected horizontally.

Taking the sharp edges down would not effect function of the locking lugs, (just do it lightly) as the part of the lug that locks with the lugs on the bolt would be those facing "downrange" on the barrel extension.

ETA: this hasn't got anything to do with M4 ramps, sheeeesh

Quoted: Exactly....  and thanks for returning us to topic. thanegrooms. The curve in the scratch would indicate that it's being done while the cartridge is being pushed forward and UP by the bolt, from it's position slightly below bore axis when in the mag and being aligned with the bore as it enters the throat. Any scratches caused by extraction would tend to be straight as the empty cartridge (or in this case with the bullet still intact) is pulled straight back by the extraction part of the cycle and then ejected horizontally. Taking the sharp edges down would not effect function of the locking lugs, (just do it lightly) as the part of the lug that locks with the lugs on the bolt would be those facing "downrange" on the barrel extension. ETA: this hasn't got anything to do with M4 ramps, sheeeesh

Of course not.  But nothing can stop the Kool Aid drinkers guzzlers.

Funny, I was going to start this same thread about a week ago, but I couldn't get a good pic.

200-10x  +1

I had the same thing happen to me a few weeks ago.

I had 10 of the new teflon coated bravo mags (D&H). I had them loaded each of them with 25 rounds of the ammo. The ammo was purchased in a 1000 round box. Loose packed, and marked for training use only. The makings on the brass are LC 02 and the little nato cross. It has a 62 grain bullet. I have shot several hundred rounds plinking with my mini 14 with no problems.

Anyhow, one of my buddies wanted to trade me for one of the bravo mags and I had to mail it to him. I had to empty the ammo out of the mag prior to mailing it. I thought I would cycle the ammo through the mag manually to be see how it functioned. (I have never "used" the bravo mag or shot any of the new ammo out one of my ARs) I had several FTF while cyling the bullets. The bullet nose was consitently getting jammed up on the feed ramps causing the scratches very similar to the picture posted above.

my next step was to try a differnent mag to see if I had the same problem. I tried a colt 20 rounder, and had the exact same results. I went and grabbed another AR and tried it with the same results. And yes I was quickly pulling back the charging handle and completely letting go of it so that the bolt would have adaquate momentum to force the round into the chamber.

After about 10 minutes of scratching my head...I tried different ammo. I loaded both mags with some 55 grain PMC i had laying around and both mags functioned flawlessly. he

There are a bunch more people here much more knowledgeable than myself. But I would suggest trying different mags and ammo to determine if this could be the problem.

Quoted: I had the same thing happen to me a few weeks ago. I had 10 of the new teflon coated bravo mags (D&H). I had them loaded each of them with 25 rounds of the ammo. The ammo was purchased in a 1000 round box. Loose packed, and marked for training use only. The makings on the brass are LC 02 and the little nato cross. It has a 62 grain bullet. I have shot several hundred rounds plinking with my mini 14 with no problems. Anyhow, one of my buddies wanted to trade me for one of the bravo mags and I had to mail it to him. I had to empty the ammo out of the mag prior to mailing it. I thought I would cycle the ammo through the mag manually to be see how it functioned. (I have never "used" the bravo mag or shot any of the new ammo out one of my ARs) I had several FTF while cyling the bullets. The bullet nose was consitently getting jammed up on the feed ramps causing the scratches very similar to the picture posted above. my next step was to try a differnent mag to see if I had the same problem. I tried a colt 20 rounder, and had the exact same results. I went and grabbed another AR and tried it with the same results. And yes I was quickly pulling back the charging handle and completely letting go of it so that the bolt would have adaquate momentum to force the round into the chamber. After about 10 minutes of scratching my head...I tried different ammo. I loaded both mags with some 55 grain PMC i had laying around and both mags functioned flawlessly. I am going to try the same test out on the range. This could have been bad. those 10 mags were my SHTF mags, and I had never tested them and the ammo together. What a rookie mistake. There are a bunch more people here much more knowledgeable than myself. But I would suggest trying different mags and ammo to determine if this could be the problem.

Your talking about a totally different thing...
Get on the same page as us...we're on page 33. Catch up

Quoted: Quoted: Exactly....  and thanks for returning us to topic. thanegrooms. The curve in the scratch would indicate that it's being done while the cartridge is being pushed forward and UP by the bolt, from it's position slightly below bore axis when in the mag and being aligned with the bore as it enters the throat. Any scratches caused by extraction would tend to be straight as the empty cartridge (or in this case with the bullet still intact) is pulled straight back by the extraction part of the cycle and then ejected horizontally. Taking the sharp edges down would not effect function of the locking lugs, (just do it lightly) as the part of the lug that locks with the lugs on the bolt would be those facing "downrange" on the barrel extension. ETA: this hasn't got anything to do with M4 ramps, sheeeesh Of course not.  But nothing can stop the Kool Aid drinkers guzzlers.

SWO...   I had M4 feedramps installed in my driveway.. and now I dont' scratch the jeep when entering the garage....  LOL

Quoted: Quoted: Quoted: Exactly....  and thanks for returning us to topic. thanegrooms. The curve in the scratch would indicate that it's being done while the cartridge is being pushed forward and UP by the bolt, from it's position slightly below bore axis when in the mag and being aligned with the bore as it enters the throat. Any scratches caused by extraction would tend to be straight as the empty cartridge (or in this case with the bullet still intact) is pulled straight back by the extraction part of the cycle and then ejected horizontally. Taking the sharp edges down would not effect function of the locking lugs, (just do it lightly) as the part of the lug that locks with the lugs on the bolt would be those facing "downrange" on the barrel extension. ETA: this hasn't got anything to do with M4 ramps, sheeeesh Of course not.  But nothing can stop the Kool Aid drinkers guzzlers. SWO...   I had M4 feedramps installed in my driveway.. and now I dont' scratch the jeep when entering the garage....  LOL

I was going to make a joke about getting M4 feedramps installed on my wife, but I don't think I have to.

Off topic: during the safety briefing at a match this morning, someone brought up that they hadn't shot a match in 10 years, and that they wished it would be like riding a bike (ie, you never forget.)  A match director said, "No, it's more like sex," and three shooters in unison said "what's that?".

Quoted: Quoted: Quoted: Exactly....  and thanks for returning us to topic. thanegrooms. The curve in the scratch would indicate that it's being done while the cartridge is being pushed forward and UP by the bolt, from it's position slightly below bore axis when in the mag and being aligned with the bore as it enters the throat. Any scratches caused by extraction would tend to be straight as the empty cartridge (or in this case with the bullet still intact) is pulled straight back by the extraction part of the cycle and then ejected horizontally. Taking the sharp edges down would not effect function of the locking lugs, (just do it lightly) as the part of the lug that locks with the lugs on the bolt would be those facing "downrange" on the barrel extension. ETA: this hasn't got anything to do with M4 ramps, sheeeesh Of course not.  But nothing can stop the Kool Aid drinkers guzzlers. SWO...   I had M4 feedramps installed in my driveway.. and now I dont' scratch the jeep when entering the garage....  LOL

Quoted: Quoted: SWO...   I had M4 feedramps installed in my driveway.. and now I dont' scratch the jeep when entering the garage....  LOL I was going to make a joke about getting M4 feedramps installed on my wife

Quoted: Just in case anyone cares...  here is what this thread is about. www.auctionadvisory.com/lugcuts.jpg Caused by the bullet hitting the sharp edge of the barrel lugs on the way into the chamber. Once when I was polishing up some ramps, I made an effort to knock the sharp edge off of the lugs and it really did help to lessen the size an depth of the cuts.

I had noticed this occuring to my new BFIs a couple years ago.   This was made apparent to me when I had a bullet fail to feed past the lugs.  I looked at the jam and noticed where the bullet was hung up at, when I ejected the unfired round, it became apparent that the copper jackets were being sliced through to the lead, most unexceptable.  At the heart of it, and not knowing if cut jackets have much negative effect on accuracy, I probably wouldn't have taken corrective measures if the jacket slicing hadn't slowed the bolt's forward momentum causing a failure to feed.

A rat tail file treatment later and no problems.

Sly