Show me your .308 AR feed-ramps

[ColoradoMinuteMan]

Request:
So, I'm looking for a little help here. I'm hoping that you can share a picture of the feed-ramps on your .308 AR with DPMS pattern barrel extension. If you can share the make of barrel an the make of the upper receiver that would help even more.

History:
We all know that the .308 AR doesn't have as much standardization as the AR-15 platform. I run into an issue that started showing itself as I began diagnosing some issues I discovered while reloading .308 ammunition from my .308 AR. At first I thought my loads were causing the case necks to split, but as it turns out it was a fairly deep scratch. I also found that there were several dents in the shoulder of the extracted cartridges. I didn't think much about it until my next range trip when I got a failure for the bolt to go into battery. It was difficult to manually extract the cartridge. I took a look at the cartridge and sure enough it had a massive dent on the shoulder.

I went home to diagnose the issue. The first thing I found was that the barrel extension was full of shavings of brass, much more than I had ever seen before. I tend to see a few flecks in my ARs from time to time but this was really bad for only shooting about 50 rounds. I made up a few dummy rounds to play with and I found the differential between my feed-ramps on the upper receiver and barrel extension was causing a nasty impact to the case neck and should which was causing the shaving and the deformed cases.

Anyway, I knew that there was not perfect alignment of the feed-ramps when I assembled this .308 AR using Aero Precision receivers and a Faxon barrel. My thought process at the time was that the smaller ramps feeding into the wider ramps will probably be fine. That doesn't appear to be the case. I know that I can correct this issue by blending the ramp using a file, but I'm not ready to do that quite yet. What I'd like to do is get a sampling of feed ramps from various vendors to determine if either the Faxon barrel ramps are unusually wide or the Aero Precision receiver ramps are unusually narrow. That way I can see which way I want to handle this. I don't want to widen the receiver ramps knowing that they will then be too wide for every other barrel extension I may replace it with down the road. If it is a matter of Faxon just being widely out of spec, I'll handle this with them. However, if it is simply a matter of Aero Precision just being conservatively narrow, then I don't mind adjusting them.

Thank you in advance.

 

[MCMXI]

Here are a couple of photos showing the feedramp in my POF P308. The ramp is scalloped (radiused) and the rifle runs like a well-oiled sewing machine with no feeding or ejection issues. I only shoot this rifle suppressed these days so the brass comes out dirty for sure but not damaged in any way. I don't use Lapua brass in this rifle but I use just about everything else including Remington and Winchester. By the way, I never clean this rifle other than to occasionally wipe off carbon fouling on the front of the bolt face and as you can see, after hundreds of rounds there's no brass shavings in the chamber or the barrel extension. The metal looks "dusty" because as I mentioned, I shoot 100% suppressed now and crap gets blown into the magazine and chamber.

 

[ColoradoMinuteMan]

Thank you. Yeah, those are nice feed ramps. One of the nice things about using a single vendor is compatibility issues are ideally nonexistent.

 

[Walkalong]

That POF looks great.

It looks like you barrel extension is a hair above the cuts in the upper. That in its self can cause issues. It it were me, I would remove the barrel and carefully work it until it looks like the POF.

Don't touch the upper.

 

[MCMXI]

I don't see the purpose of the scallops in the upper receiver below the feedramps. Also, it's likely that you don't need two separate feedramps for left and right sides of the magazine, so as Walkalong suggested, maybe you should break out the Dremel and carefully blend the feedramp into one surface rather than two. The feedramp in my POF P415 is the same as the P308 i.e. one surface. If you go that route it would be interesting to hear how it turns out.

 

[ColoradoMinuteMan]

I spoke with Aero Precision and shared with them the picture.

My message:

[ColoradoMinuteMan Name Omitted] | January 3, 2017 9:21:02 PM PST
I built this M5 using an Aero Precision upper and lower receiver as well as an Aero Precision BCG. The barrel is a Faxon 18" .308 Win 4150 QPQ. I'm having some issues that I believe are related to the feed ramps on the upper receiver. The feed ramps are much narrower than those on the barrel extension. This difference is causing the cases necks to scrape across the hard corners which results in dents in the case shoulder as well as a lot of brass shavings. The dents in the case shoulder are to the extent that occasionally a cartridge will not fully go into battery. I've thought about filing down the feed ramps to widen them but I'm concerned that I may make a mistake that will cause further issues. I've checked another DMPS barrel and it also appears to have wide feed ramps on the barrel extension, so I don't think that the Faxon barrel is out of spec. Suggestions?

Aero Precision:

[Aero Precision Customer Service Name Omitted] | January 4, 2017 10:32:31 AM PST
Good Morning.

Thank you for reaching out to us. Unfortunately we do not guarantee fitment with other manufacturers products however it looks like the barrel just doesn't match up. I would contact Faxon and see if they recommend a barrel that will work with your feed ramps. Sorry for any inconvenience and if you have further questions please feel free to contact us.

We've had more back and forth since then and I asked them to send me a picture of one of their assembled uppers for comparison so I could compare the difference in feed ramps on their own Aero Precision barrels. Take a look at the side by side photos. I'll let you decide what you think of Aero's response.

 

[MCMXI]

What do you think's the purpose of the two cuts below the feedramp? The nose of the bullet contacts the feedramp directly during the feeding cycle, not those cuts below the feedramp. Surely your brass damage and brass shavings are due to the feedramp geometry.

 

[ColoradoMinuteMan]

What do you think's the purpose of the two cuts below the feedramp? The nose of the bullet contacts the feedramp directly during the feeding cycle, not those cuts below the feedramp. Surely your brass damage and brass shavings are due to the feedramp geometry.

My understanding that the "cuts below the feed ramp" are they are actually part of the feed ramp. To my knowledge these evolved when the feed ramp angle was changed from 45 degrees to 52 degrees. The change of the angle resulted in needing to extend the feed ramp into the receiver. It is my understanding that this was one of the "improvements" introduced to eleviate feeding issues that occurred with the faster cycling M4 gas system as compared to the M16A2. I have no idea if this is a valid reason to have them in a .308 AR, but the barrel extensions are designed with a similar feed ramp angle that anticipates the feed ramp extending onto the receiver. The tip of the projectile indeed does hit the barrel extension directly however, the shoulder impacts the feed ramp extension on the receiver.

What do you think is the purpose of the "two cuts below the feedramp?"

 

[MCMXI]

The tip of the projectile indeed does hit the barrelextension directly however, the shoulderimpacts the feed ramp extension on the receiver.

My POF doesn't have cuts in the upper receiver below the feedramp and yet the rifle functions flawlessly. So to answer your question, I think that the cuts serve no purpose whatsoever. I suppose it's possible that POF machines the P308 lower in such a way as to make the magazine sit higher in relation to the bolt but I doubt it. My P415 is very similar.

 

[ColoradoMinuteMan]

My POF doesn't have cuts in the upper receiver below the feedramp and yet the rifle functions flawlessly. So to answer your question, I think that the cuts serve no purpose whatsoever. I suppose it's possible that POF machines the P308 lower in such a way as to make the magazine sit higher in relation to the bolt but I doubt it. My P415 is very similar.

Yeah, unfortunately there is a lot of variation between makers so it does make comparison a little more difficult. Who knows what variations may account for various issues. I do like the feed ramp setup on the POF barrel. I don't fundamentally think there is an issue with the feed ramp extensions. I'm guessing the majority of AR-15s on the market have M4 feed ramp extensions and it doesn't seem to inherently introduce any issues. I think it is just the variation that is causing some issues. I'm going to just start by softening some of the edges and see if that helps. It could just be a sharp edge that is causing the issues.

 

[Walkalong]

If it was .223 it would be M4 cuts in the upper, but it isn't, and even if they are intended to be an extended feed ramp, the barrel doesn't match up.

Personally, I would work it carefully and make it match that POF. If you are not comfortably doing that get a gunsmith to do it.

 

[ColoradoMinuteMan]

If it was .223 it would be M4 cuts in the upper, but it isn't, and even if they are intended to be an extended feed ramp, the barrel doesn't match up.

Personally, I would work it carefully and make it match that POF. If you are not comfortably doing that get a gunsmith to do it.

Well, I'm positive they they are intentional extensions of the feed ramps. It's really the execution of which I'm curious about.

 

[Everready73]

Try contacting Nathan at Faxon. He is pretty active on some other forums and is always helpful. I think he might have a user name here but if not it's on their website. If it's on them they will take care of it

 

[ColoradoMinuteMan]

Try contacting Nathan at Faxon. He is pretty active on some other forums and is always helpful. I think he might have a user name here but if not it's on their website. If it's on them they will take care of it

I reached out to Faxon last week. He got back to me today and we have started up a conversation. He seems anxious to help me, so I look forward to it. I doubt it's a Faxon issue based on what I've learned so far. Aero Precision customer service wasn't as great as I had hoped. After using their products for quite a while I was disappointed at their response. Especially because I wasn't asking for a replacement, or money back, or anything, simply trying to get more information. Their initial response was (paraphrased but seen above) "talk to Faxon and get a compatible barrel, we make no guarantees on fitment." All of which I can understand, but I wasn't asking for anything other than information and it wasn't a great starting position.

 

[maxxhavoc]

Just saw this.
PSA PA-10 Upper. Needs cleaning.

 

[Everready73]

Try contacting Nathan at Faxon. He is pretty active on some other forums and is always helpful. I think he might have a user name here but if not it's on their website. If it's on them they will take care of it

Sucks to hear about the response you got from Aero. Faxon makes quality stuff and i would be surprised if its on them, but hopefully they have an idea how to make it work. One thing you could try as far as Aero goes is to visit them on their industry forum on ar15.com/forums. The rep there for Aero has been active lately and seems to be pretty responsive. Maybe taking that route will get better results. I know it has for a few others that got nowhere with customer service.

 

[MCMXI]

Here's the feedramp in my POF P415 which is basically a scaled down version of the P308 shown above. You can see some brass rubbing on the feedramp but no shavings, no M4 feedramps, no peening of the lower below the feedramp and yet no feeding issues. It seems obvious to me that no part of the cartridge case makes contact with the vertical face below the feedramp so I still question the need for those cuts in an AR-15 or AR308.

 

[Nature Boy]

That is one clean chamber MCMXI. You're not shooting it enough

 

[MCMXI]

That is one clean chamber MCMXI. You're not shooting it enough

HA! HA! Haven't you heard the myth that "piston" ARs run a lot cleaner. That rifle has hundreds of rounds through it without cleaning, many of those shot with a suppressor attached.

 

[ColoradoMinuteMan]

So, I wanted to circle back on this. I worked with Nathan at Faxon who helped my through some troubleshooting. As it turns out the cause of the scratch on the neck, projectile and the cause of the brass shavings is two different things. After taking a hard look at the spent brass and the dummy rounds I ran through I can see that the shavings are caused by a really aggressive extractor. I guess I don't have to worry about having any FTE due to a weak extractor. I wasn't able to replicate those shavings during a manual extraction due to the lack of energy involved to shave off a piece of brass.

The scratch on the projectile seems as though it was due to a really sharp edge on the feed ramps in the barrel extension. You could feel it when you put your finger up inside the locking lug and it even caused me a little cut on my finger tip. Nathan advised me to due a light polish on that seemed to dull it just enough to no longer be an issue. So, all has been resolved, and I had a successful trip to the range today. In the end it had nothing to due with Aero Precision feed ramps and I don't think that any part of the cartridge even touches that part of the receiver when loading. Aero and Faxon were both responsive to messages and I appreciate that. Faxon though deserves and extra tip of that hat in how they handled the service. Nathan was really eager to help, asked a lot of questions and gave some good advice for trouble shooting. Aero lacked slightly in their approach which was not really asking any questions and making some assumptions. In the end they gave me the info I asked for, to troubleshoot, it just seemed as though they were convinced from the first message that they didn't think it was their problem. They were indeed right, but they just didn't seem eager to help. Oh well, I don't think it will stop me form buying their parts because I still think they are good value, I just won't expect stellar service.

Thanks to everyone who posted.

 

[MCMXI]

In the end it had nothing to due with Aero Precision feed ramps and I don't think that any part of the cartridge even touches that part of the receiver when loading.

Yeah, I've made that point at least twice in this thread already.

 

[ColoradoMinuteMan]

Yeah, I've made that point at least twice in this thread already.

You did indeed. "YOU WERE RIGHT." Happy now?