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+--- Thread: 14.5" AA upper failure to feed (/showthread.php?tid=10928)
14.5" AA upper failure to feed - mike1 - 03-06-2016
I'm having a problem with a failure to feed on a 14.5" AA carbine upper. I'm using PPU 120 gr ammo, although I've had problems with Wolf MPT and Wolf soft point. I've used multiple lowers and I still experience the problem. Today I was using a Mega lower with an A5 extension, Springco green spring and both a A2 and A4 buffer. I've used a carbine extension with multiple weight buffers in the past. I was using an E-lander magazine today, although I've used C-products in the past. The cartridge ends up driven into the case and the meplat has an indention across the tip like it hit a corner. My current diagnosis is that the meplat is hitting the barrel at the throat of the chamber. I saw a picture of a Grendel barrel and it appears to have a chamfer at the entrance to the chamber. My upper does not appear to have any chamfer. I've looked at one of my 556 rifles and it has a chamfer at the entrance to the chamber. Is the chamfer optional on a Grendel barrel?
A little history, I purchased this upper a long time ago. It's always given me fits. I first thought this was a magazine problem give the terrible QC of C-Products magazines. I stuck it back in the safe. I purchased some E-lander magazines and still had problems. I stuck it back in the safe. I recently read a thread that bullets with meplats are sensitive to feed ramps so I pulled the barrel and worked on the feed ramps. Today was my first outing since working on the feed ramps and things went better. I use to get bolt over brass and some pretty mangle cartridges. Today I didn't get any bolt over brass though I'm still getting FTF. The absence of bolt over brass failures today could have been because of the feed ramp work or maybe the A5 extension is slowing down the bolt.
Any ideas what wrong?
14.5" AA upper failure to feed - LRRPF52 - 03-06-2016
Does it work with the CProducts mags?
Your chamber does have a chamfer to it. If it didn't have one, there would be a sharp edge plainly visible. It's standard for every rifle maker I know of to chamfer the entrance to the chamber.
14.5" AA upper failure to feed - Bill Alexander - 03-06-2016
These were set up to run on a regular carbine spring and an H2 buffer. They are near optimally set up for bolt speed with a carbine length gas tube. (use one for my truck/work gun)
The fault occurs when the magazine lips do not control the cartridge, bolt speed is too fast (indicated by the BOC failures) or the bolt is gripping the cartridge as it pushes forward.
Give the office a call if it is still giving problems and I will get it in and sort it out.
14.5" AA upper failure to feed - mike1 - 03-06-2016
LRRPF52 Wrote:Does it work with the CProducts mags?
Your chamber does have a chamfer to it. If it didn't have one, there would be a sharp edge plainly visible. It's standard for every rifle maker I know of to chamfer the entrance to the chamber.
It didn't work with C-Products.
Ok, I looked at the pictures more closely and what I thought was a LARGE chamfer was the change in color between the barrel and barrel extension.
14.5" AA upper failure to feed - mike1 - 03-06-2016
Bill Alexander Wrote:These were set up to run on a regular carbine spring and an H2 buffer. They are near optimally set up for bolt speed with a carbine length gas tube. (use one for my truck/work gun)
The fault occurs when the magazine lips do not control the cartridge, bolt speed is too fast (indicated by the BOC failures) or the bolt is gripping the cartridge as it pushes forward.
Give the office a call if it is still giving problems and I will get it in and sort it out.
I'm pretty sure I've tried an H2 buffer but not sure if it was with a blue springco spring or a standard spring. I've had this upper since 2008 and I didn't document every configuration I've tried over the years. Is this upper that sensitive to spring/buffer configuration that only a standard spring and H2 buffer will work?
14.5" AA upper failure to feed - mike1 - 08-07-2016
After a bit of time off, because of a broken arm, I got a chance to work with this upper again. I sent the upper to AA and they said there was carbon buildup in the gas port so they cleaned it and sent it back. I took it to the range and the third shot:
[ATTACH=CONFIG]8005[/ATTACH]
[ATTACH=CONFIG]8006[/ATTACH]
[ATTACH=CONFIG]8007[/ATTACH]
This was with a H2 buffer, carbine spring and an AA 10 round mag from years ago. The ammo was PPU HP BT 120gr. I didn't have any problems for the rest of the box. I then ran 60 rounds through a ELander mag without problems.
I'm sure some would say it's a magazine problem but I've had this type of failure with several different magazines. This problem is intermittent. I can go 80 rounds and not see a failure.
Can this type of failure be caused by something other than a bad magazine and if so what?
14.5" AA upper failure to feed - VASCAR2 - 08-07-2016
unfortunately there have been bad batches of PPU ammo, especially being inconsistent. I never experienced this much variation with Wolf but the PPU is suspect. If you got a cartridge with lower recoil impulse you can have this failure to feed. I had similar problems trying to shoot 123 grain Nosler bullets with to light a charge of CFE 223 powder in my 16" carbine gas length 6.5 Grendel.
Without having the exact velocity of that particular round before the failure to feed you have no proof. I suggest you try different ammo, Hornady A-Max, SST, ammo from AA or PF. My handloads are more consistent than the PPU 120 grain HP BT I've purchased.