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Old June 29, 2013, 01:09 PM   #1
Mohave-Tec
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New rifle build failure. I'm calling for an AR doctor here.

I finished building my first AR 15 yesterday. Here it is in its earliest carnation.



So even though it was 100 degrees at 8:30 this morning at 4000 feet elevation I wanted to at least get out and run the barrel in. Now I've put together numerous bolt guns before and I'm a pretty handy mechanic but my experience this morning was dismal. I couldn't get off 2 rounds before a failure occurred. In the desert I wasn't able to make any determinations as to what was going on but back here at home after cleaning up the gun I am seeing some issues. Please give me a hand if you can?!

I hand load. I've developed 2 loads for other 223 rifles I have (KelTec SU16C and a Savage Axis 223) so I started out with the simpler hand load for those guns to run the new barrel in. The load on the middle is that load. It is a Remington 55gr Power-Lokt over 24.5 gr H335 with a COL of 2.182 to mimic the factory load sold at Wal Mart. The load on the left is a 60gr VMax over 25gr of Varget with a COL of 2.250. On the far right is one of the many Power-Lokt rounds I killed in my upped receiver this morning on its way to cambering. The next picture sounds one of these rounds nearly folded over.



I know next to nothing about ARs but I know other rifles. It looks as if I am having fail-to-eject issues then I'm slamming a new round into the back of the still chambered but spent case in front of it. What is doing this? I have a couple suspicions but would love to hear your opinions.

The rifle is currently a Frankengun. I got it in my head a couple weeks ago I wanted to build an AR and though I want a certain quality, I was obliged to pick up what I could in some cases if I wanted to get this thing built in a month. Some of the hardware I believe might be to blames. Here it goes.

In this picture you see an fairly well made AR Stoner 18 inch mid gassed Wylde chambed barrel over extended into a slick sided DPMS upper. First thing that bugs me is the feed ramp alignments. Not only is the barrel's feed ramps further into the receiver than the receiver's feed ramps but clearly the right feed ramp aligns but the left ramp does not. I think both the depth and alignment issues are making my rather short reloads bounce and making it difficult for them to chamber. What do you think might happen here?



Also, with the 18 inch mid gassed barrel I have an adjustable gas block on it but the adjustment is wide open as I cannot tell the relationship between the gas port and the jet (set screw) that regulates gas flow in the block. This and the buffer weight is 2.9 ounces when I'm thinking something much heavier might help with this gas/barrel configuration? Maybe?

Lastly, and what scares me the most is that it is a BCM BCG that is failing to eject the spent cases from the chamber. Why would this be?

I'd appreciate any help I can get on this. Since I am in "very hungry nube learning mode" I am going to cross post this thread in another forum to see how much I can learn about all this.
Thanks again.

Oh, by the way, this rifle is majorly accurate and the most repeatable off shoulder 200 yard COM I have ever shot......f I can keep it shooting.
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Old June 29, 2013, 01:55 PM   #2
Metal god
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Couple things I can think of to check .

My first thought is under gased . Could be a few things that cause this .

1) Does the bolt lock back on final round ? If no , gas issue . Maybe gas block not centered over port either front to back or left to right , gas tube or block leak , Gas key leak . check gass rings on bolt

In your picture it looks like you have a good size gap between your gas block and rail . On my mid freefloat rail with railed gas block they are almost touching . You can see the gap but just barely and you have to hold the rifle just right to do so . can you puss the gas block back a bit ?



If bolt locks back on final round check the ejector and make sure it's moving freely with enough tension to throw the brass .

Maybe extractor is letting go of the brass prematurely .

I checked my book and both those loads should work but sometimes what looks good on paper does not work in the field

Thats a few things I can think of

Last edited by Metal god; June 29, 2013 at 02:13 PM.
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Old June 29, 2013, 02:29 PM   #3
allaroundhunter
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Re: New rifle build failure. I'm calling for an AR doctor here.

Not undergassed, but over. If the bolt is cycling but not removing the empty from the chamber then you have too much gas which is propelling the bolt back faster than it can hold onto the rim of the case.
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Old June 29, 2013, 02:33 PM   #4
Nathan
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One step at a time here. Is it ejecting the first round or is that staying in the chamber?

Your bent gouged case tells me the bolt is riding over the case in the mag. It still often half strips it by digging in and gouging it. This is almost always not enough gas. As above, check all leak points.

IMO, the most suspect leak point is block to barrel port alignment. I would remove, measure crown to port on barrel, block front to block port and subtract. That gets the axial right when you reinstall. Then mark center of port on block and use a ruler to mark barrel port center. If you do this well, alignment will be perfect.

Is there some other way to check this?
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Old June 29, 2013, 03:55 PM   #5
Mohave-Tec
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Hello all. Thank you hugely for lending a hand.
Actually, I am hoping like crazy that my issue is over gassing. When I was reading about mid gassed longer barrels I read that an H2 buffer weight may be needed but all I could find is a 2.9 oz carbine weight. I have an H2 on the way and my gut, just from firing the gun the first time this morning is telling me my extractor just needs a milisecond more time to get a bight on the spent case. This is also why I bought an adjustable gas block but I have no indicator as to how far the adjust the jet (well, set screw actually) in the block incrementally. Anyway, I brought an allen wrench to the desert with me this morning just for this purpose.....only to find it still in my living room when I got home.

These things AND I not sure about the gasket we are talking about?
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Old June 29, 2013, 04:02 PM   #6
Mohave-Tec
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Nathan, I was looking at the gouges and trying to fit their spacing with the width of the feed ramps but with your note I do see that the gouges are actually the same distances apart as the tanks on the bolt. It will be a pain but it is time to witness the gas post/gas block relation. I will do the measurements too. BTW, more often then not, it is not ejecting the first round.
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Old June 29, 2013, 04:48 PM   #7
Mohave-Tec
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When all my best guesses fail me I have to revert to pure science. So, I made a tapered gasket out of scotch tape wrapped around a computer cleaner compresses air tube then shoved a spent round all the way into the chamber then stuffed the canned air into the chamber side gas tube and put my face to the muzzle. No question about it. We are getting all the gas we'll ever need. LOL.
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Old June 29, 2013, 04:48 PM   #8
Metal god
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Does The bolt lock back after last round is fired .Important to know if locking back every time cus that would mean it has enough gas. I'd do a few more test before taking things apart and then only fix one thing at a time then test till problem is solved
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Old June 29, 2013, 05:10 PM   #9
Mobuck
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Load 1 round in the mag, chamber it, and fire. If the bolt locks back each time, you're getting plenty of bolt travel. Then load 2 rounds, fire round 1, and see if the second chambers. If this doesn't work, check you magazine. That's the extent of the detective work I've encountered on the AR. Well, other than the strange variation that was so over gassed, it was feeding two rounds per cycle.
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Old June 29, 2013, 06:38 PM   #10
Mohave-Tec
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These will be the next steps. I'm pretty sure it is an over gassing problem. Next Friday i will find out either way. It it is over gassing I will pick up an H2 buffer weight on the way back in from the desert.
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Old June 30, 2013, 12:45 PM   #11
Nathan
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Why would you think it was overgassed? Overgassed is hard to achieve, unless you had the gas port larger as a custom order. IIRC, AR's are designed to push back the carbine spring, H2 buffer and FA BCG. That is max reciprocating mass, with nominal or max pressure ammo.

I thought adjustable gas block were for rare case builds(18" barrel, carbine gas length, etc) or for having a custom oversized port cut to run lower recoil/pressure ammo for gaming or suppressor use. On a std middy AR, I see no use, but it might be your issue somehow.

So, to be clear....the spent case is not leaving the chamber?
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Old June 30, 2013, 01:08 PM   #12
Mohave-Tec
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OK everyone. The hard work has paid off.
I wrapped a piece of cellophane around an air tube on a can of compressed air and placed it in the chamber side end of the gas tube. Then I put an expanded/spent case in the chamber. I wanted to see if I could judge the degree of valving I was getting with the adjustable gas block. I tried this yesterday but I was trying to feel how much air us being released at the muzzle end. I just couldn't tell.
This morning I tried it again but this time by sound. I gave the air can a very short burst with the gas valve at what I believed to be nearly closed. It took about 3 seconds for the "bleeding off" sound to dissipate. I opened the valve a quarter turn and it took 1 second to dissipate. open another quarter turn and a shorter time to dissipate until It only took about an eighth of a second for the bleed off sound to dissipate. Fantastically, this sound test works very incrementally and I was very able to judge the degree of jetting the gas valve was doing. I then closed the valve until it took about 2 seconds to hear the air bleed down then I went to the desert. I took a different ammo with me than I used yesterday but I also took some of the same ammo. This morning I started by putting two of the same reloads in the rifle as yesterday. BANG, eject, feed, BANG and the bolt locked back. I repeated this a couple more times with 2 rounds. The bolt didn't lock down only one time. I closed down on the valve 1/8th more turn and the rifle ran perfectly on subsequent tests. They I loaded the magazine to 28/30 rounds and let it rip. Never a failure. It ran perfectly with the short hand loads and the rough honed feed ramps. Then I filled it up with the VMAX loads I developed for my Savage 223 bolt rifle. These are the finest bullets I have ever reloaded consistently making compound holes at 100 yards. The AR LOVED them and I was hitting a piece of typing paper off shoulder at 220 yards every time I pulled the trigger......with a red dot. What a fantastic workout.
I'm still going to but an H2 buffer. With a carbine buffer and the H2 I can configure any common buffer weight by mix matching parts from both buffers. I want to see if this will let me be able to make even more intricate adjustments at the gas block by leaving a little more of the port open. Other than this, I'm going to clean up the feed ramps then commence with some better optics and a few other toys to finish dressing it out. Again I thank you all so very much.
I want to add an un-related peice of information before I close. I had to buy a lower parks kit in order to build this rifle. Almost nothing was available and I certainly didn't want a bottom floor trigger in the rifle as I have always put aftermarket triggers in my guns. I was unhappy that I couldn't get a known trigger for the gun but I was happy to find something that called itself an improved trigger. I never heard of this before but out of necessity I bought a lowly 'Del-Ton Enhanced Lower Receiver Parts Kit with Two Stage Combat Trigger Assembly' for a modest $124 from Midway. I am here to tell you that this is the sleeper value trigger of the decade. It doesn't break like glass or drop the hammer at .25 pounds. What it does do is stop and a very discernible second stage at nearly the end of the trigger pull, drops at about 4 pounds then resets in the same place every time. I think this trigger is the new gotta have it trigger for the duty bump and crash rifle. If you ever what to make just a budget rifle I highly suggest you look at this trigger. I may not even replace it in this rifle when "better" triggers become more available.
Now, off to optics but that's another thread.
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Old June 30, 2013, 03:04 PM   #13
Metal god
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Very cool . You were right the whole time , over gassed . Like I said above I would not have went there first which means I was not the doctor you were looking for . Just to be clear . The ONLY thing you did to get the rifle working properly is adjust the gas block to the right pressure ? very cool easy cheap fix.

Last edited by Metal god; June 30, 2013 at 08:15 PM.
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Old June 30, 2013, 05:27 PM   #14
Mohave-Tec
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It would appear that was the issue the entire time.
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