I just finished a build on my first .308 platform AR. Parts list is as follows:

- Anderson 18" mid length barrel
- Anderson free float rail and barrel nut
- Anderson low profile gas block and mid length gas tube
- Anderson matched upper and lower receiver
- Anderson lower parts kit
- DPMS rifle buffer tube and spring
- Ultimate Arms rifle buffer
- Magpul PMAG

    I went out to test. Cheap Russian steel cased .308 145 grain ammo. I pulled back the charging handle and the round jammed angled halfway up the feed ramp. I tried a couple more times and still the same result. I tried to put a round in manually and it got stuck in the chamber. After I finally got it out, I thought maybe it is the feed ramp/chamber. It was not polished up at all. I polished it up and it will let the rounds slide in and out with ease. Still won't feed into the chamber from mag. The bolt locks back when I pull the charging handle with an empty mag in it. I dropped the mag and it released the bolt for some reason. Same result every time I tried it. I manually put in a few rounds to test fire with no mag. Shot perfect. I then loaded one and put the empty mag in. Shot fine again. Didn't lock back. Weird. I decided I would try to manually lock back the bolt. Locked back and stayed. I decided to put a mag in it with a couple rounds and see if it would charge. I released the bolt catch and the BCG went forward. I thought it charged. Click. I dropped the mag and inspected the chamber. No round ever went in. I picked up the mag and it had just scraped up the casing a little on the top round.

    Basically, what do you guys think might be the issue?  The cheap ammo (which I kind of doubted since it shot and extracted)?  The PMAG (since the rounds wouldn't chamber from it)?  The buffer spring (it looks a little long and feels a little stiff)?  The bolt release?  Help please!

Pull the charging handle to the rear and lock the bolt back. The bolt catch should be on the bolt head. I'll bet yours is catching on the front of the carrier. The Ar 15 and the AR 10 use the same length spring with the same wire size but the coil count is different. If you have a spring with too many coils it won't allow the bolt to travel far enough to the rear.
Check this out.
http://heavybuffers.com/reference.html

Anderson barrels have extremely tight chambers.

You have experience with Anderson barrels that have tight chambers...........308??? explain your experience

S
If it's not picking a round off the mag it's probably not a chamber issue, just a guess here but I'm pretty sure about it.

Thanks for the info! Now that I look at it, that is exactly what is happening. It is catching on the front of the carrier and not on the front of the bolt. Should I just get a new spring or should I trim some coils off of my existing one? First .308 I've ever done so I have never had to deal with an issue like this.

How many coils is it?  And the length?  
You might need a different spring and your buffer and tube might not be matched.
My brother got a parts kit that had a rifle spring in a carbine buffer tube/buffer combo. It did the same thing. $6 fix

Both rifle length. Both DPMS. Looks to be roughly 38 coils.

Measure the buffer. A dpms buffer should be 5 1/4 long where a standard ar15 or Armalite ar10 is 5.1/2 iirc.
The 1/4 inch would be about the distance that you need to get it to lock back.
Edit: Looked it up. A standard ar buffer is 5.9 long.
Like I said earlier. Look up info here. http://heavybuffers.com/reference.html

And would you look at that. There is my problem. My buffer. It is too long. I took out the spring and dropped the buffer in there and it still would not go back far enough. Stopping at the same spot. Took the buffer out and pulled the BCG back into the empty tube and it goes back plenty far enough. I will have to get a different buffer. Thanks for all the help.

Anytime I can be of help its a good day. Lol. Your welcome, and welcome to ARFCOM I forgot to add that earlier.

Something I hadn't considered. I always use a A2 stock and spacer since I'm so tall and have a long LOP. The dpms 308 buffer is shorter than a standard 5.56 or Armalite 308 buffer though.
Edit ipad autoincorrect strikes again.

AXC .308 RIFLE LENGTH Solid Fixed A2 Stock Kit Buffer, Spring, Buffer Tube

Bought one of these and am using it on my Palmetto State Armory PA 10 .........works like a champ. 46.95 shipped

The chamber thing is only relevant to this comment:

"I tried to put a round in manually and it got stuck in the chamber."

I have a 20" Anderson and a friend has an 18", both headspace correctly, but the chamber diameters are very close to the minimums, as some factory ammunition is tight and sometimes you have to mortar the things to get rounds out.  When you shoot it, no problems though.

He also stated "the rounds slide in and out with ease".

That was the feed ramps.

Okay, thanks for the information........I have an Anderson 20" that I am going to use for an upcoming build.......have heard nothing but good things about the barrel until you mentioned something about it..........thanks

Shoots great though....

Just need a small base die to reload.

I hand tightened the barrel to the upper receiver nice and snug...........chambered a round of ZQ1 7.62x51 and closed the bolt.........was able to extract with the charging handle with no issues...........