Check your feed ramps?

[Redleg]

Though my M4 seemed to function allright with the first magazine through it, I did find quite a few teeney brass flakes when I took the bolt out to clean it. A lot of my brass also had a slight pinch half way between the shoulder and rim. I found out later that the pinch was actually coming from the HK magazine. As the round is forced forward and up, the steel magazine corners were binding into the brass. I compared to one of my old GI mags, and those were slightly beveled up to allow the brass up and out. I need to pick up another HK to compare and see if mine just got pushed in or not, I think I straightened that part out with needle-nose though. T suspect the tiney, squarish, brass flakes were from the front edg of the brass catching on the front edge of the steel magazine, after the bullett cleared it. I checked this on the other magazine as well, it also hit, though not quite as abruptly. This happened with federal and remington .223. I need to pick up some real 5.56 to see if it acts the same way with a heavier slug and shoulder area.

When checking out my magazine situation, I was cycling a few rounds and discovered the brass jacket on my bullets were being cut into by a feedramp. This was almost an S-shaped cut, raising a little edge on the brass. I checked the reciver and found a burr-like high spot along the back edge of the left feed ramp. I know this was not there prior to firing, I think it was just distinct enouph I would have spotted it. It may have gotten pushed over after firing. It was on the right side of the left ramp, as if a bolt lug forced it back as the bolt was rotating back open on the return cycle. I took a small, steel rod and ran across this edge a few times to force it down. I cycled a few more rounds through this and this time the mark was still there, but only a scratch, no raised brass. Now I intend on touching up these edges slightly with a tiny round file. The raised cut was definitely significant enouph to effect accuracy. I'm not blaiming the manufacturer so much as chalking it up to "getting to know your new weapon". Also, I am currently set up with a semi-auto carrier with commercial buffer. Maybe a more violent extraction raised the metal if the manufacturer did their test fire with a heavier BC and Buffer? I DO intend on an FA bolt and maybe H-buffer to try soon.

**** Be careful and know where the gun is pointed if you cycle rounds through. The firing pin free floats in the bolt and could contact the primer when doing your function check. I have some prior experience, but am not a pro.****

Also, if anybody was wondering, the .223 brass has a (slightly detectable to the eye) swollen/steeper shoulder after being fired through the 5.56 than the the unfired rounds.

[Redleg]

Pictures didn't work out, gonna try again later.

[Fronty Owner]

yea, pictures would be helpful...what Upper doyou have? Your sig says the upper is coming soon...

[Redleg]

Sorry, its at the bottom. CMMG 14.7" M4 upper. It was nothing that would creat a safety hazzard on the ramp. Wouldn't be noticeable if you didn't extract an unfired round. Definitely an accuracy concern. I think it would be something to watch for from any manufacturer.

[Redleg]

As promised...

The sharp edge I described cutting into the bullet jacket was on the inside, rear edge of the left feed ramp in the circle. I used a small rat tail file and polished that edge. Also, it's not a great picture, but if you see the reddish, verticle lines on the feed ramps, that's the fresh brass markings on the path the bullett tip takes into the chamber. When being fed the tip first contacts the ramps right where the extension meets the reciever, showing why it's important not use an M4 reciever with a standard extension. The reciever here is anodized over the ramp cuts.

The other picture is the "pinched" case on the right and the offending edge of the HK mag on the left. Sorry it's dark, the brass glare wanted to wash out the picture.

[Redleg]

Here is where the case tends to catch the magazine when being shucked/ fed into the reciever. It was more pronounced on the single HK mag I have, than the older, military issued mags. Again, this was with 55 gr. commercial .223. Heavier, Nato rounds may not interfere so much, but I haven't had the opportunity to compare yet. Also picking up some more HK mags and will check for consistency.

None of these issues have caused me a misfead or any other real, mechanical problem. When checking a round for the ramp scratches, extract it slowly and even hold it in-line with the bore as you draw it out. The round will want to angle out against the locking lugs and the extractor spring is strong enouph to cause the fresh, sharp, lug edges to also scratch into the jacket and throw off your findings. My rounds are now all coming out clear on inspection.

[Equalizer_2]

Magazines are the heart of a semi or full auto. They can make or break a design.

[Redleg]

A little further research. I've read of other feading issues with the HK mags. A lot of guys don't like them. Seems like the complaints grew as M4 ramps became in demand more? I suspect part of the issue being the M4 ramps allowing the rounds to stay lower in the magazine longer. I haven't had much chance to shoot latley, but have a lot of time off coming. I do intend to shave down the forward edge of at least one magazine to be even with the feed plate. ALso haven't recieved my M16 carrier yet.

[tightgroup]

It is hard to tell what is happening from your pics but I would definitely try an H-buffer. The M16 carrier is not going to change things that much.

I run commercial mags with the Magpul kits(heavy spring and anti-tilt follower) and PMAGs in mine with good success.

[Redleg]

Originally Posted by tightgroup

It is hard to tell what is happening from your pics but I would definitely try an H-buffer. The M16 carrier is not going to change things that much.

I run commercial mags with the Magpul kits(heavy spring and anti-tilt follower) and PMAGs in mine with good success.

Thanks, I was even actually contemplating at least an H-buffer. I did some more shooting and there was dramaticly less brass on the bolt face since releaving the pressure on the HK tabs. ALso, not a single scar or indication of pinching to the case from this magazine. A better camera is in the works and with my vaction next week, I'll clean this up some hopefully. Also, being broke in further, the lugs are taking a lapping now, so things are looking better there. Not so sure the brass bullet jackets would've polished off that back edge of the feedramp anytime soon, without my intervention.