looks like a common problem with so many variables?  maybe someone had this exact issue and can give me a fix.

RA Ultramatch 18" rifle gas barrel
RA Billet upper
RA Thunder Chrome BCG
PRI Gasbuster CH
Lower is a proven lower before I started swapping out parts.  I swapped out the trigger and installed a Magpul PRS.  Other than that, no change.  I may swap a proven upper with this lower if needed.

Had multiple magazines on hand to test today.  30rd CProduct aluminum.  15rd Magpul . 30rd D&H.  30rd ETS
Ammo used was 60rds of old Guat M193.  60rds of Magtech 77gr(MK262 clone). 10rds of SW 75gr 5.56.  
Magazines were only loaded with up to 10rds each.  Sometimes 5.

This upper was assembled by me about 2-3 years ago and never fired.  Took it out today and was very disappointed.

So I'm all pumped and ready to fire my first shot.  Put in my 1st magazine(Magpul) and pull CH. Aim and pull trigger.  Click and nothing happens.  Pull CH again and double feeds...  Drop magazine, 1 cartridge drops out.  I pull the CH and a live round comes flying out of the port.  Hmmm

Put the magazine back in and pull the CH.  Click.... I drop the magazine and pull the CH but nothing comes flying out.  I pull the CH again to make sure to clear and sure enough, a cartridge comes flying out.  So I'm thinking maybe it's just a tight fit.  So I disassemble the upper and BCG and tried to run it really wet with CLP.  

With no magazine.  I run the CH multiple times to see if it would help loosen up.  Maybe 10 times.  It appeared to go into full battery every single time without a magazine.  

I insert my magazine and try again.  BOOM with first shot.  Then click.    I'll drop the magazine.  Rack CH and insert magazine.  A few times, I was able to fire the entire magazine without issue.  Again, remember, magazines only loaded between 5-10 rds.  Sometimes less, since I had rack the CH so many times with a live round flying out.  First thing I notice is no dimples on these live rounds.  

When I would chamber a round with the CH, I would see my CH wouldn't go all the way forward.  It would stop just shot of the notch to lock up.  I would slam my FA and this would move the BCG forward and lock the CH.  Sometimes, this was enough to fully lock the BCG and will fire.  Sometimes, it looked like it was fully forward, but just click when I pulled the trigger.

About halfway through, a few times I was having issues with pulling the CH back after a failure to fire.  It felt like the BCG was seized in there.  I was worried I would have to mortar the CH, but grunting and pulling enough was able to get it loose.

This happened with every single brand of magazines I mentioned.  When I had a good series with a magazine. I would try to use that one again and issue will pop up.  My fingers are sore from racking that CH I don't even know how many times.  The barrel was shooting great for me when I was able to get a string of shots going.  This issue was working in my favor at first, since I was breaking in the barrel.   But man was it annoying.

So it looks like my BCG will almost go into full battery, but just stopping short!  When I got home, I was cleaning the upper.  I made sure to clean the chamber really good just in case there's some residue or whatever in there.  I did notice what I would consider odd wear in my upper receiver.  I don't remember my others looking like this.  I also removed the o-ring from the BCG when I got home.  I don't think it's needed and could be a potential problem with too much extraction power and not being able to open up and grip the rounds and it's going into battery?

Let me know what else you think I can or should do.  Thanks

Ditching the o-ring was a good first step.
There was a recent thread where the forum moderator had a picture and explained what the extractor should look like installed.
It would not hurt to check headspace if you did not when assembling the upper.

Is your charging handle dragging in the upper?
There is what looks like a big strip of wear in he upper.

Here's what my PRI CH looks like.  It has a nub on the top.  I do not feel any resistance at all when I'm sliding the CH back or forward.  I believe this is what's causing the wear up top.






Dano, your first reference image doesn't work, so I'm not sure what you're referring too exactly.  But here are closer and better shots of my feedramps and barrel extension.







I removed the bolt and see if the gas tube was causing any bindings.  It feels good to me.  If I have the CH locked in place.  I can grab the carrier and lift it back a few inches and let it freefall and it'll hit the face of the extension without issue.  


If I wasn't clear in my original post.  When I would have the bolt locked back.  Insert a magazine.  Then hit the bolt release, the bolt wouldn't go 100% all the way forward too.  I want to say it didn't even go into full battery once doing it that way, but I'm not sure of that now.  

 There's no way I was riding the CH.  That was my first thought when it happened the first time.  I was thinking, did I accidently ride it, even though it was unlikely.  I made 100% sure I pulled all the way back and release after that.  I wonder if the buffer spring is bad.  I find that hard to believe though, since my other rifle is much older and no issues.

Also, no way I overloaded the magazines since this range only allows up to 10rds per magazine.  I remember having a couple 2rd and 4rds in the magazine after grabbing my spit out unfired cartridges.

After I removed the o-ring. I ran some snap caps with a magazine.  I can tell the snap caps are smaller than real cartridges.  But at home, I was able to chamber a round using the bolt release.  I couldn't do this when I was at the range.  I may remove my firing pin and test several live rounds to see if it will chamber.  Is that a good/safe way ?  If I can chamber a live round by using the bolt release, that will be a huge improvement already....

I think mine looks good to me.  






One thing that annoys me is, this "Chrome" BCG doesn't feel like chrome or look like Chrome.  At least not like Young's .  It's almost a matte "Chrome" finish.  Feels dull.  But you know, as long as it works, I'll be happy.

OP, don't try to chamber a live round without the firing pin installed.  The cam pin will rotate and get bound and you will have a hard time unlocking the bolt within the barrel extension (with a live round in the chamber).  Your chamber looks clean.  Was it that clean when you were shooting?  I had the same issues and it ended up being a small piece of blown primer that had become wedged in the barrel extension.  It was physically keeping the bolt from rotating to lock. I would pull the trigger and hear the click, but no primer strike.  Once it was removed, problem fixed.

If you have another bcg, try it. The oring gave me headaches on one upper, but was fine on my other rifles.

I don't know if it's a shadow and I can't circle it on my phone, but in your feed ramp pic look close at three to four o'clock on your barrel extension. Is something making contact there or just an illusion?  It looks like contact from the bcg. If it's not the right dimension or the extension is proud your bcg could be stopping before the cam pin fully operates keeping the bolt from rotating home. This is pure speculation and I've never heard of it, just trying to help. But your extension does look slightly peened from the front face of the bcg

An old trick for finding contact on metal parts. Spray a light coat of paint on the suspect area ( bcg, bolt, extractor, and upper). Operate several times , take it all apart and look for the shiny spots. Clean with brake parts cleaner or your solvent of choice.

One thing to add, your bcg is chrome lined on the bolt cavity, not a "chrome bcg" the outer coating is phosphate per the advertisement

To my knowledge, the chamber was clean on the first outing.  Granted, I didn't clean it right before I headed out.  IIRC, I cleaned it about a month ago.  I should say "lubed" it a month ago.  I cleaned it when I was assembling(2-3 years ago) it.  Thanks for the heads up about the firing pin.  I did not know about that issue.  

Like I said, as of right now, I can release the bolt on a magazine with snap caps and it chambers without an issue.  But I can tell the snap caps are a tad smaller than a real cartridge.  Pretty sure I have some AE .223 that I can bring with me next time just in case.

I checked my other uppers and the markings appear to be normal.  In one of my pic of the extension, it does look like there might be a divot or ding, but it must have been an illusion from oil.


Also, this BCG is "Chrome".  I mean, look at it, lol.  I've never seen silver colored phosphate BCG.  The BCG was bought a couple of years ago.  It appears they no longer sell them.  Which makes me wonder why.....

Alright, just got back from the range and the issue has improved drastically, but this rifle is still not 100%.  I'm having 100% failure to feed when using the bolt release.  It will require me to pull the charging handle to load the cartridge.  This will work 90% of the time.  The other 10%, I had to pull the charging handle a 2nd time to feed the cartridge.

I also had 2 failure to fire.  "Click".  Pull CH to eject round.  I didn't see a dimple on the cartridge, but saw a dirty spot where the firing pin was just far enough to make contact.  I'm going to guess it's because the bolt wasn't all the way into battery.

I brought 4 different types of magazines with me.  EVERY single magazine couldn't load with bolt release.  

Magazines used today.  Brand new Lancer AMW 30rd smoke.  Magpul 15rd.  ETS 30rd.  D&H 30rd.  D&H (w/ Palmetto floorplate) 30rd.

With the aluminum magazines, I had a few issues where it was single shooting only.  I had to rack the CH to load the next cartridge.  Same issue with the Lancer.  Did not occur with the ETS or Magpul though.  Those were fine once I started firing.  

Started off with 80rds of IMG M193 that's heavily corroded.  Then 20rds of AE223 55gr.  Then 50rds of CBC(Magtech) 77gr.

Here's my shopping list.  I'm thinking new buffer spring, new BCG, and new CH.  Well, I have a standard CH.  I think something is binding in my upper.  

Just got done cleaning it.  So here's some pictures before the cleaning incase someone see something out of the ordinary.  The only thing that looks different to me is the markings on top of the lower receiver from the CH and the markings on the bottom of the BCG.  I don't remember seeing these on the other ARs.

Some stuff that looks odd to me.  I think you may have multiple problems going on.

The lube and carbon displayed on your dirty BCG around the gas key looks odd.  It is as if it is blowing out from somewhere it shouldn't be.  Check your gas rings for wear or breakage.  It may just be the picture, but your rings don't appear to spread enough while sitting out of the BCG.  When I lay a bolt down its side like that, the rings push out to one side and protrude more than what I see in your picture.  Your rings appear to be too flush all the way around.  And are you spraying lube in the gas tube?

Your charging handle wear looks odd on the left side, looking from the top, and on the bottom, same side, where you have that worn squarish area near the handle.  It looks like your upper is too small on one side, or the charging handle is large on the one side, and it is binding up just shy of fully closing.  While it is probably latching closed, if it slows down at that point, it could be preventing the bolt rotating and locking that last little bit, and if it doesn't rotate all the way, the firing pin will not strike the round.  You should be able to check this by letting the bolt go home and then pressing the forward assist and see if the BCG rides forward that last little bit.  The wear inside the upper also looks odd.  They all show wear in there, but yours looks excessive.  If the charging handle is not fitting correctly, with all those pressure points, it could be slowing the BCG down as it cycles.

You mentioned not seeing primer strike.  Even without firing, and just chambering a round, you should see at least a tiny hint of indentation because the firing pin is free floating on the AR.  If you don't, that might mean the BCG is not making it all the way forward, or the bolt is not rotating to the point of full lock.

Your barrel extension looks odd.  At first, it kind of looks like a mild version of mismatching M4 feed ramps with a non-M4 style barrel.  But after closer examination, it looks like your barrel extension is sitting too deep in the receiver.  It looks like you lapped the receiver face, and took entirely too much material off, allowing the barrel assembly to sit to far into the upper.  Even if the rounds are not catching on the exposed lip, that condition changes the angle at which the rounds are presented to the chamber, and might be causing them to get caught on the feed ramp.  If you didn't lap it, the barrel extension could have been made to long, or the receiver face milled too short.

I didn't read everyone's posts, so i'm sorry if this has been said.  But that wear on the inside of the receiver looks......  intense.  I wonder if the charging handle is binding your BCG.  Is there that kind of wear on the inside channel of the charging handle?   Where the gas thingy from the bcg rides in?

I think part of my part was originally with the o-ring in the bolt.  I also think my upper receiver may be on the tight side.  It is a billet.  Maybe the BCG and CH are on the higher end of the specs?  I have a spare generic CH.  I will bring that with me next time.  I will also bring an extra BCG with me.  

I'll probably bring another AR to swap lowers and such.


I've never milled or lapped anything.  Everything is as is, from the break in process.

I did notice additional wear on the left hand side of the CH when I was cleaning it.

Not visible wear on the inside channel of CH.  I do see wear on the outside.  Especially on the left side.

So I received a set of these dummy rounds.















They are shorter than the real deal too.  I loaded up 10 of them into 5 magazines.  

15rd Magpul
30rd ETS
30rd Lancer AWM
30rd "Palmetto" floorplate D&H
30rd D&H

Everything single one allowed the bullet to chamber properly when using the bolt release.  Almost 0 issues chambering using the CH.  I did have 1 issue where the 2nd round in the Lancer popped up into the chamber by itself.  So when I released the bolt, it created a double feed.  The reason I know this happened is because I was watching the ejection port when I pulled back the CH.  The rifle was pointed downwards and saw the round pop right out and slide right into the chamber.  Have a nice dent now on one of the cartridges.

So yeah... I'm thinking I'll find some more dummy rounds that are closer to the real thing.

There is something going on with that gas tube. It appears bent and/or like it is binding inside the gas key. Check for gas tube/ gas key binding. Also remove both the bolt and charging handle from the rifle and check the charging handle fit to the bolt carrier group. If the handle is wedging between the gas key and the top of the carrier that will cause the charge handle to drag inside the upper which can make a mark like yours.

Less replacing stuff, more measuring stuff.

In all of those pics, there doesn't appear to be near enough lube.  I thought these things were supposed to be run wet?

Also, if this upper has less than a few hundred rounds through it, why are we getting our panties bunched?  It's going to be tight.  I hand cycled both my builds 100-200 times dry before I took them to the range.  No problems.  On the first range trip with the 300blk I was next to a gent who was having feed issues similar to the OP here.  Bcg was basically dry, and after assembly he had never cycled it.  I lubed the hell out of it, he hand cycled it about a dozen times, then back to live rounds.  No issues.  

Contact surfaces are going to show wear.  Surfaces that aren't supposed to be in contact but show wear (like the side of the gas tube where the key is rubbing it...) are of concern.  Edges of the ch where they ride against the upper receiver would seem to me to be a non issue.

I disagree on the gas tube assessment. Looks good and is smooth when I push the BCG into battery.  Now the 2nd part, will need to test.


I did receive new dummy rounds that look like the real deal. Rifle functioned without issue using the bolt release with every single different magazine used.

Haven't gone to the range since last outing. I'm thinking things are starting to smooth out slowly.

I suspect its a combination of issues. I think the billet receiver is really tight. I think the CH might be on the high end of the specs. I also think the BCG is scraping the top of the bolt release and/or hammer. As you can see in the pics of the bottom of the BCG.

I'll know for sure the next time.