308 AR build help please

[Crazydoc68]

Well I got the upper in today. Looks great!!! Everything was tightened down. Matched up perfectly to the lower. I immediately replaced the flash hider with a muzzle brake. Will be mounting the scope later today and then taking her to the range Saturday. Will follow that up with some good pics and a range report.

Doc

 

[SAWMAN]

CAUTION: it will be super loud Doc with a brake unless it is of the "linear" style. I have a linear brake on my gun and it still kinda loud but without the "right back at ya,flip your hat off" overpressure. --- SAWMAN

 

[Crazydoc68]

Im well aware of the blast now. Wish I knew before when I had my bolt 308!!! I use double hearing pro. Getting older now and hearing isn't getting any better!!!

 

[FLO]

Finished the build yesterday. I lubed it up with slip 2000 (bolt, charge handle, chamber, ramps ect) and tried to chamber a round out back and bent several rounds near the base of the bullet. I let the charge handle back all the way and let go, also tried doing it slowly to watch the round and see if it was hanging up anywhere but didn't notice anything. I used a few 308 rounds and also 7.62 with similar results and all 4 of my Magpul gen3 mags. Unfortunately I don't have other mag brands to test.

The AIM bcg and Mega barrel passed the go/nogo headspace test. I have another AIM bcg on the way so I can test. I may order a different mag brand to test as well. I wonder if the Mega chamber is just very tight. Kinda disappointing after over $1.6k. The 2 successful chambers out of 10 attempts has the bcg lock in and the round extracted fine so I'm stumped at the moment. Any suggestions?

My parts list is a bit different from my original post:
Mega 16" barrel
AIM Nit BCG
Aero Prec M5 LPK, buffer kit

 

[SAWMAN]

........"base of the bullet"....... Are you saying that the deformation is down AT or BELOW the neck of the brass(assuming the bullet is 168grs or heavier(longer) ??

Maybe -> carefully drop a rd into the chamber and let the carrier down onto it until the extractor claw snaps over it. Gently extract/eject it and see if the same damage appears. Could the freebore be short ? Could the chamber neck be short ??

I would not think that a MagPul mag would not do this to the brass. They are slippery plastic. I have never seen a MapPul that would not allow proper feeding.

Have you tried a FACTORY LOADED 308Win rd ?? --- SAWMAN

 

[FLO]

This is when I drop a round in by hand. There's a small scuff below the neck.

And here is attempt to charge with full spring action.

Bent round.

 

[FLO]

Sawman I'm testing with factory Hornady SST 150grain, 7.62 L2A2, and Federal 168 bthp match.

 

[Brandon_SPC]

I do have still have a stripped upper receiver from DPMS that has never been used if you would like to buy it. Keep you from spending extra money on shipping and finding a good deal online. Maybe 4-5 months old. That's the upper. I posted a picture from midwayusa so you can compare the two to show it is a DPMS.

 

[Marquezj16]

How's the barrel extension to feed ramp fit?

 

[Crazydoc68]

Was just about to say that myself. Make sure M4 feed Ramps on upper and on barrel extension.
Do they look/feel rough. How is the chamber? Is there marchining marks it or smooth?

 

[FLO]

The feed ramps and barrel extension are a bit different. The feed ramps are much smaller than the extension ramps but there's no rough edge for the round to get stopped at. I plan to trim the feed ramps a bit. The rounds get stuck in the same place whether I let the ch-handle go from all the way back or I help it slowly to see what's going on. The round goes up the ramp fine. I'm almost thinking the problem is with the barrel extension or the chamber. Everything is clean and looks smooth inside the chamber.

 

[bigbulls]

I can tell you by looking at where the forearm meets up with the receiver that your barrel nut is not aligned properly. That shouldn't cause a feeding issue like you are having but it will cause problems when you start firing the rifle. Check the face of the bolt to make sure the bast of the cartridge isn't hanging up on the extractor cut or extractor itself or some other spot on the bolt.

 

[FLO]

I can tell you by looking at where the forearm meets up with the receiver that your barrel nut is not aligned properly. That shouldn't cause a feeding issue like you are having but it will cause problems when you start firing the rifle. Check the face of the bolt to make sure the bast of the cartridge isn't hanging up on the extractor cut or extractor itself or some other spot on the bolt.

Yeah it was a tad off. I put it back on the vise and loosened/tightened and lined it up. That's fixed. Now I need to figure out the feeding issue.

 

[Marquezj16]

Can you take a pic of the inside of your receiver to show the extension and feed ramp?
If they are not matching up, the bullet tip could be hanging up on the extension.

 

[FLO]

Here's the feed ramps/barrel extension. I need to dremel them but were they meet is smooth so I'm sure this is the cause of the problem.

thanks for the help everyone!

 

[Marquezj16]

Oh wow. That's quite the mismatch. I am almost 100% sure that the feed ramp is the problem.

 

[Telum Pisces]

Oh wow. That's quite the mismatch. I am almost 100% sure that the feed ramp is the problem.

Yep!!

 

[Crazydoc68]

Holy moly. Looks like feed ramps for 2 different calibers.

 

[FrankT]

take a pic of yours Doc for him to compare

 

[Crazydoc68]

Here's what mine looks like.