Alright I did my first AR build.  I built a 300 blackout upper to go on my DPMS lower that I already had.  Used Wilson Combat upper receiver, barrel, and lo pro gas block. Shot it the other day and it would not auto at all. I know this isn't an uncommon problem for this round.  I read some on it and I found everything from drilling the gas port out to just changing magazines to be solutions.  After reading I decided that the gas port I don't believe is the problem.  I would think that Wilson combat would do their research and know that the gas port on their barrels were not large enough to reliably cycle the bolt.  So I emailed Wilson Combat and they seem to think its all in the magazine.  So today I took my buffer and removed 2 of the 3 weights that were in it and changed to the stock 30 round mags that came with my DPMS.  I could then get about 2 or 3 shots off and would have to rack the bolt because it didn't chamber a round. Also the first time out shooting even though it wouldn't chamber a round when the last round in the mag was fired it would lock the bolt back.  So I'm pretty sure its the mag.  I plan on trying a magpul pmag.  Anybody have any input on this?  Think I should add weight back to the buffer?  Anybody have any trouble with pmags? Also does number of rounds the mag holds makes a difference?

And yes I know about 300blkouttalk however I couldn't get registered to post there.  Kept saying too much spam from this domain. I don't know I figured this would be the next best place.

Thanks for all the help.

Number 1 I would replace the weights in the buffer.

First question I have is, what ammo are you using?
Question number 2, what length is the gas system you are using?



As for magazines. I have been using military surplus mags I took when I left the army. I have 20 and 30 round mags. I have had zero failure to feeds due to magazine.
I would l

I would start by looking at your gas system. Gas block, gas tube, gas rings and gas key.

Let's wait until we have the first questions answered before we look further.

If you truly think it is the mags, number your mags on the bottom. If you are the problem with the same number mags the. More it out of the rotation.

Im using a carbine length gas system.  I used a couple different types of ammo.  Today were I was getting it to auto a couple round I was using Remington match 125gr OTM. The first time I shot it I was using some subs and then some Percision One(?) 150 gr noslier ballistic tips that I picked up at a gun show.  Got the gas block from Wilson combat and the gas tube was UAG I think(picked it up off amazon).  The BCG came from my DPMS ar that I already have as well. I know that you cant have too much gas when it comes to the 300 blackout but if gas was the problem how could it lock the bolt back?  Wilson Combat said that they set their barrels to run a standard carbine buffer but I thought I'd try to take some weight out. I believe the bolt is coming back far enough because I can see marks in the casings where the bolt rode over top of them.

Do you have a bad lever on it?

Tag....  My Wilson 300 barrel will be delivered on Monday!

What length is your gas system?  
What length is your barrel?
Will the bolt lock to the rear when the magazine is loaded with a single round?

I'd check the gas port (measure using a drill index)
Verify gas block alignment
Check gas key tightness
Check gas rings

Im using a 16" barrel and carbine gas systemi . It will lock back if there is nothing in the magazine on the last round fired.  Where are the gas rings? I checked the alignment on the gas block today as well and it is lined up. gas tube as well. Im impressed with the barrel. Setting the scope my last 2 shots were inside an inch circle.  Also Wilson Combat have great customer service they go above and beyond for their customers.  Where are the gas rings located? In the gas key im assuming?  How can I check the gas key? This is my first build and I have a basic knowledge of how the system operates but I am by no means an expert.  Thanks for all the help guys.

Without sounding like a moron.........what lever?

The gas key is on top of the bolt carrier.  It's the tube looking thing that is bolted on top.  If that's loose, and gas leaks at the joint between the carrier and the key itself, it can cause problems.

The gas rings are on the bolt itself, on the end that lives inside the bolt carrier.  Take the bolt carrier apart, and pull the bolt out.  You'll see them, there are three of them...or at least there should be.  Post pics, if you can, as well (of everything, not just the bolt)

He was talking about a Magpul B.A.D. (Battery Assist Device) lever.  It's thing that bolts onto your bolt catch so you can activate it with your index finger in the trigger guard.  Their only purpose is to look cool, and cause malfunctions

Fire a few rounds in your .223 AR with that bolt to troubleshoot it.
then maybe try a heavier buffer like an H2?

With all you said, i would try a different bolt since you are using a used one. I would also check gas block alignment.
As for ammo, I would stick to factory until you get it running. Having an unknown reload throws in a extra factor.