Feed ramp issue?

[philpac33]

I have a relatively new build and have been able to get out to shoot it 5 times thus far, between 90-150 rounds per outing. On it's maiden voyage I had 2 malfunctions, both times the tip of the bullet got hung up on the feed ramp.
http://i1300.photobucket.com/albums/ag99/philpac33/5CCF8F10-647C-4CEA-B656-4A380606F824-2283-000002E6220C9CA0_zps04f242e6.jpg
Since then I've had no stoppages but the feed ramp issue is still a problem. When I drop the bolt on a new magazine, a round is chambered as it should but if I don't allow the full strength of the buffer spring slam the bolt home(i.e. ride the charging handle at all) I get the same jammed up round on the feed ramp. Also, upon inspection of rounds chambered and ejected, every single one of them has a scrape/gouge mark on the bullet. This happens using Pmags, Troy Battlemags, and several brands of USGI; 55 and 62 grain bullets.
http://i1300.photobucket.com/albums/ag99/philpac33/93CD7D1D-AC56-41A0-8905-13F1023B5F52-2283-000002E6254D6371_zpse5cea6e3.jpg
The upper is an Aero Precision(M4 feed ramps) and it is a Rainier Arms Select 5.56 barrel. To the touch, the transition between the feed ramp and barrel extension is smooth. In the pic above you can see some copper on the right ramp. I've searched and found lots of threads on various forums regarding jams on feed ramps and on feed ramp bullet gouging but none of them actually came up with the cause for this and in turn no solutions(unless you consider polishing feed ramps a solution). Like I said, the gun has actually run 100% since that very first trip but I still feel the feeding just isn't right. I spend time everyday reading and learning here on Weapon Evolution; the combination of very knowledgable, helpful members and the lack of chuckleheads I see elsewhere keeps bringing me back. Thanks.

[csmith]

If you built your lower (or even if you didn't), check to ensure your magazine catch is fully engaging. Another full turn into the mag release could help. The premise behind that is if your magazine isn't fully engaged as it should be then your magazines may be riding a hair low, and therefore your rounds are sitting lower than they should as well. While you're at it, check your magazine catch to make sure it's still serviceable for the same reason. I know it's new, but life happens. After that check to ensure your buffer spring is serviceable.

I'm thinking what you're saying you do is utilize your charging handle to release the bolt (e.g. pulling the charging handle back and releasing it to close the bolt on a full magazine). If that's the case, don't do that. Just use your bolt release. As you've found out, if you hold the bolt up at all it can cause these exact issues as well.

[CLBME]

I have learned that it's not an uncommon situation after having my build shown the same issue. I am finishing a mid-length build using a BCM barrel and Aero Precision upper. The feed ramps on the upper "undercut" the feed ramps on the barrel. Nearly identical to yours. I did a Google search a while ago and found several posts where people have run into the same issue. And yes, the solution I found was "polishing" the ramps for a smooth transition. As far I as I have been able to learn it's simply a potential outcome of building the rifle from various parts and not necessarily "wrong".

[Eric]

Also, upon inspection of rounds chambered and ejected, every single one of them has a scrape/gouge mark on the bullet. Normal. The round is still under tension from the ejector and the round contacts the barrel extension/lugs as it's pulled free from the chamber.


When I drop the bolt on a new magazine, a round is chambered as it should but if I don't allow the full strength of the buffer spring slam the bolt home(i.e. ride the charging handle at all) I get the same jammed up round on the feed ramp. Also normal, for the most part. The round should be chambered by letting the BCG slam closed under maximum spring compression from the action spring (aka buffer spring). I can induce a malfunction on just about any AR if I slowly chamber a round.


To the touch, the transition between the feed ramp and barrel extension is smooth. In the pic above you can see some copper on the right ramp As long as you don't have a pronounced ledge or gap there, you're good. M4 cuts appear to be on the upper as well as barrel extension, so that's good. It's not uncommon to not have them match up perfectly, especially when using parts from various sources.

At this point I would not change anything. Just ensure that it's somewhat clean, well lubricated and shoot the gun.

[RiverRat]

I worked through the same issue with my 16" Rainer Select barrel.

During initial function testing, inserting a mag on a closed bolt led to exactly the same "round jammed into the ramp" failure - even when I didn't ride the charging handle.

I broke my upper down and rebuilt it, making sure I was on the low side of the recommended torque range on the barrel nut. I also lubricated the heck out of my BCG. No other changes made.

No problems since, though with limited round count to date (less than 1K fired).

[philpac33]

Thank you for the replies, they are all much appreciated. It's reassuring to hear that this issue is not all that abnormal in a rifle cobbled together with components from various manufacturers. My plan was to just keep shooting it as long as the feed ramps didn't cause any more malfunctions (it's run 100% the last 500+ rounds) so to hear suggestions telling me to do exactly that is very encouraging. Just to be clear Eric, you say these scraped/gouged bullets are normal as well; is the bullet being scraped while being chambered or as it's being ejected?
http://i1300.photobucket.com/albums/ag99/philpac33/2825DAA4-005B-4F56-8828-747657055C62-4162-0000073250B4F28B_zps9b165af0.jpg
The green tips above are generally representative of what I've experienced but a few others have been much deeper and nastier. If the marks are from making contact with the lugs upon extraction, that's acceptable. If it's happening as the round is being chambered, would a heavily scraped/gouged bullet affect accuracy at distance? By no means is this rifle supposed to be a bench rest tackdriver but significant damage to the bullets would have to have some affect on making combat effective hits at considerable distance. My rifle is clean and lubed(I'm still lubricating my NiB Fail Zero BCG), magazines topped off, and have a gameplan on the drills I plan to run tomorrow. Hopefully it continues to run sans malfunction and I can put this matter to rest. Again, thanks to everyone that replied.

[philpac33]

Bright sunny spring day today was conducive to a productive training session. Ran another 210 malfunction-free rounds down the tube. That gives this rifle 5 consecutive trips(720 rounds) running 100% since those 2 feed ramp jams on its first outing. I've been semi-anal about keeping it clean and well lubed regardless of the BCG and FCG both being NiB coated. A small piece of me is still a little worried about those feed ramps but I have high hopes that the more I shoot it, the lower the chances are of them giving me a problem. It feels good to start having confidence in this build.