View Full Version : AR15 - A problem with the upper, or something else?

04-11-2011, 4:51 PM
I'm an AR15 novice and just finished assembling my AR15 and took it shooting yesterday. All of the parts are new. I bought the upper completely assembled.

Every shot was having problems with the bolt carrier not picking up the next round from the magazine after ejection. From what I could tell the bolt carrier is traveling back far enough to eject, but not quite far enough to catch the next round from the magazine. This is also apparent, since when the final round from the magazine is fired, the bolt carrier does not lock behind the bolt catch consistently.

By racking the charging handle after every shot, I'm able to successfully pickup a round from the magazine and fire/eject almost every time (over the course of 100 rounds or so, I did get about 5 ejection failures that were cleared by racking).

I tried:
- different brand magazines
- different brand ammunition (brand new Fiocchi and PMC)
- extra lubrication on the bolt carrier assembly and various other points of contact
- reducing the tension on the buffer spring
- checking the gas key for air flow, proper seating

There is an increase in resistance while pulling the charging handle, which I'm fairly certain is from the hammer applying upward pressure on the bolt carrier when racking (so you're not only fighting the buffer spring, but also the hammer spring while racking). Due to my limited experience with AR15's, I'm not sure if this is normal or not.

I took some photos and can take more if it might help provide more insight to the problem. Let me know what you'd like a shot of and I'd be happy to take it.

So, what do the experts think about this?

Bete Noire
04-11-2011, 5:03 PM
Check the weight of the buffer. The heavier ones have an "H" printed on them. Yours could be too heavy. I've also had out of spec charging handles that drag excessively on the sides of the upper. Once the hammer is reset, it shouldn't be draging on the bottom of the bolt carrier too much. Your pic shows an unusual shape to the upper edge of the hammer that is different to the ones I'm used to. Best of luck.

04-11-2011, 5:12 PM
hard to say. could be your whole buffer spring assembly. try with a whole new stock assembly kit

04-11-2011, 5:14 PM
Its the hammer. Definantly the hammer. Get one without that notch and it will be good to go.

04-11-2011, 5:18 PM
manufacturers of components of the rifle would be useful, what length barrel and length of gas system.

04-11-2011, 5:20 PM
Its the hammer. Look at it.

04-11-2011, 5:21 PM
It also looks like (could just be the angle of the picture) the Bolt carrier isn't flat on the bottom, that the right hand side is sunken in.

04-11-2011, 5:21 PM
Well I will give a couple things to check-
1-resistance is normal for compressing the hammer and the point in your pic appears right.....now are you sure you have the hammer spring installed correctly...ie if you compress the hammer back by hand does it bind or travel and lock back smoothly?

2-Too much lube can be as bad as not enough- wipe most of that excess off the parts and specially off the gas rings IF you put any on them and wipe the bore in the carrier out/dry. Also while you are in there you MUST stagger the slots in the 3 gas rings for proper function(order and replace these with a 1 piece one from Armalite or other source). As long as the bolt rotates and moves freely you should be GTG on this

3-Is it possible thst you are using an A2/FULL length recoil spring in your (apparently) Carbine length recoil tube...they are NOT the same length and neither are the buffers. If you did not buy the stock and buffer/spring assy as a unit then I would ask to borrow a buddies or buy a carbine buffer and spring set and try it...or compare to a friends 'unit' if a friend has a similar setup.

3- I would try to verify the gas tube is completely clear free of obstruction or conversely look around the gas tube/block and check for unusual amount of blowby...ie not enough gas pressure going back to carrier.

Basically either you have a low gas pressure ,a physical binding problem........basically since you covered the ammo and mag issues ...the rifle seems to be 'short stroking' for one reason or another.....

I commend you on doing the trouble shooting that you did...covered the basics.

Final thing to try-- wipe all the parts mostly dry and sit there and with out a mag...cycle the rifle like 30 times using the charge handle and then take it apart and look for obvious signs of wear,galling,binding,etc it should be very obvious if it is a phisical obstruction that way... and like I said, see if you can compare or borrow a known carbine length buffer and spring assy and try it..

good luck and hope this helps.

04-11-2011, 5:29 PM
Your rifle is short stroking.
To narrow this down you need to load 1 round only into the mag and see if the bcg will catch after firing. If not it can be a problem with either the bolt catch or the gas system.
More likely the gas system.
Check the gas key on the bcg for any play. Check gas block with hand guards off and see if any carbon leakage (dark grey/black) is visible. Check if gas tube is loose and intact.
It looks like lube is not a problem but normal running will require less than I see in your pics. Just do the 4 contact points with grease and the bolt's rings and call it good.
Good luck.

04-11-2011, 5:37 PM
....now are you sure you have the hammer spring installed correctly...ie if you compress the hammer back by hand does it bind or travel and lock back smoothly?

...Too much lube can be as bad as not enough- wipe most of that excess off the parts and specially off the gas rings IF you put any on them and wipe the bore in the carrier out/dry. ...


That ^^ pretty much follow everything he said you should be GTG. I over-lubed my AR and it had failure to feeds. i cleaned it, dried it, and slightly re-lubed. ran flawlessly.

next thing that came to mind was inporper trigger assembly, probably the hammer spring was installed wrong?

Also, i had a hard time from the pictures, but are there M4 feed ramps? i heard if you don't have them there could be more issues of feeding problems..

PS. i don't think its the actually hammer itself, i have an AR15 style (the one with the notch) hammer not an M16 style and i have no problems with it. I also have a full auto BCG, still no issues so...

04-11-2011, 5:38 PM
I had an identical problem with a brand new upper. I ended up finding black residue leaking our of the gas block after oiling it and shooting it a few rounds(20). The gas block was not properly installed, so air/oil was able to find its way on the outside of the barrel.

04-11-2011, 6:39 PM
Besides what has been said already regarding hammer or buffer or gas system, I'd consider a different type of lube. Looks like your using grease and for AR's I prefer oil. This is definitely a short stroking issue. Just have to isolate the source of the problem.

04-11-2011, 6:47 PM
who built this Upper? Check the gas key Bolts, check the gas tube, .... first off...who assembled the upper?

04-11-2011, 7:28 PM
I would get all of the lube off of the receiver and charging handle. Make sure the roll pin holding in the gas tube to the gas block is there. Next check gas tube alignment. It looks like the buffer is a car. Make sure the gas key is tight, and properly staked. My guess is bad gas tube alignment, or missing roll pin.

Edit: I just read Your captions, and I am now thinking it may be the hammer.

Tank 57
04-11-2011, 7:36 PM
Had the same problem with an upper with excessive headspace.Had to have it rebarreled.

04-11-2011, 7:45 PM
Regarding the Hammer- I see a build up of lube on the notch edge-looks like grease, other than that I see no obvious flaw...if that grunge area on the notch edge is actuall a hammer defect there should be no way that thing got out of the factory....now IF the hammer is not machined correctly down lower and causing EXCESSIVE binding then I would agree...but there would also be a HUGE galling streak going down the hammer face and the carrier bottom.

This is one of those 'eff it bring it over and we can sort it out' problems...pics and discriptions of what is going on are very important.

I still suggest borrowing anothe buffer/spring assy from a friend(if you have a friend with a carbine-come on you MUST) and lay yours next to it and compare-easy enough to see if something is preventing full travel..

If this is good then check for blockage in gas tube or excess fouling around the block

Last is the hand cycling with minimal lube so you can SEE or NOTICE any excessive galling.....

It should take 1-2 hrs MAX to sort it out....again still glad you confirmed it was not the mags.....

Regarding M4 vs NON m4 feedramp ...the rifle should still feed without issues regardless of the feedramp style..none of my AR's have ever had the M4 ramps and they have fed fine.

Sorry I know I repeated some things.....AR's are really not that complicated .

04-11-2011, 7:51 PM
I bought the Magpul CTR stock as a kit. So it came with the buffer tube, spring, and buffer all included. They aren't Magpul parts, so it's very possible the spring/buffer are not carbine size. I already destroyed the buffer spring in attempts to reduce the tension (note that this did not have any positive or negative effects on my problem). So I'm definitely going to try this out.

The lower parts kit is RRA, and I bought it straight from the manufacturer. Moving the hammer by hand, it locks in place and releases with the trigger no problem. It seems really smooth in motion, but it does require some firm pressure to push down. Now that you guys mention the hammer issue, I went and looked at the hammer from the RRA parts kit, and it's a different shape, looks rounded and not notched. Check this out and compare it to mine:

I tried varying amounts of lube while I was out in the field. Luckily I had a variety on-hand while I was out, nothing I tried seemed to make a difference. When I took the pictures, it was a bit excessively lubricated (was doing some more testing with grease/oil).

I contacted the person whom I bought the JD upper from, which is also who assembled it. It's still under warranty and he is willing to replace it (although with some delay), but I really wanted to rule out any other problems that could be my bad (novice error).

I'm going to check and see if I have the appropriate tools to remove the quad rail to get a closer look at the gas tube. I can hook up some air to it and see what happens.

Should the gas tube from block to BCG be completely air tight, or is it normal to have a minimal amount of air escaping?

Thanks guys.

04-11-2011, 7:53 PM
Its the hammer. Look at it.

just looked at the pics...LOL

1) get all that Vaseline off of the BCG
2) replace that hammer.....

04-11-2011, 7:55 PM
Edit: I just read Your captions, and I am now thinking it may be the hammer.
Yeah, that's what I'm thinking. Trigger function needs to be verified.

04-11-2011, 7:58 PM
check the back of the buffer for wear. I had something kid of like this where the top stock screw was hitting the the back of the buffer and it wouldn't let the buffer go al the way back. I ended up throwing the screw into my tap cutting 1/4 inch off then taking the tap off. Worked great.

04-11-2011, 9:13 PM
Buffer spring length and buffer are carbine spec.

A helpful bit of info:
Rifle: 11.75 in. min to 13.5 in. max
Carbine: 10.0625 in. to 11.25 in. max

Took the hammer off and confirmed it's positioned correctly with the spring, based on the Brownells vid. No problems there. The weird little lip on the hammer in the picture is just excess grease. I should have cleaned everything better before photographing.

I just finished some testing with the gas tube and compressed air. If I plug the chamber, the gas tube inside the upper receiver, and the muzzle, air is clearly escaping from around the gas block. I'm not sure if it's supposed to be air tight or not though.

04-11-2011, 9:15 PM
What would the different hammer have anything to do with it? Isn't that just an older design? Only problem I've heard of that type of hammer is catching on the firing pin but the shielded bolt carrier should have solved that problem.

Should be a real tight seal between the gas block and the barrel. Sounds like you found your problem.

04-12-2011, 7:48 AM
Where are you located? My hammer looks just like yours and have never had any problems at all..