I built this AR and it failed. AR15 scientist help much appreciated!!!

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taliv, the rounds eject every time when I pull the charging handle and let it fly. No problem. I also had a professional AR builder check out the BCG yesterday and the BCG checked out just fine but I expected it would.
I will do a close examination of the chamber this morning but rounds that do fire and eject look just fine.
 
If I read "adjustable" gas valve, try turning it down, and do check the chamber for roughness.
 
Top-o-the-morning to you all.
It's 86 degrees in Las Vegas this morning at 5:30AM. I'm packing up again for the desert before it reaches 117 degrees. Right now I'm doing an experiment to try to establish where the jet is about to meet the port on my adjustable gas block. I didn't have a wrench for it yesterday and it was wide open. I've exchanged my gen2 PMAG for a gen3 and an aluminum magazine. The only store bought 223 I have is Hornaday Tap, a couple very expensive boxes leftover from pre-reloading days so I'm taking that. I'm leaving home my 2.120 COL Power Lokt over H335 and taking 2.250 COL Hornaday VMAX 60gr over Varget. Gas block wrench in hand and chamber snag test passed. I'll let you know how it goes in a few hours.
 
No. I don't have any reason to. I can all but pull the spent cases out of the chamber with my fingernails and the newly formed hand loads drop right in the chamber just as they are supposed to. I don't know much about the small base dies, probably because both my Lee and RCBS do just fine as is. Am I missing something?
 
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but but it is a mil spec bolt lol. I had the same problem with a rem AR 308 sent it back 3 times finally they trimmed the extractor spring. before it threw empties 20 ft. I had the biggest buffer and spring and I was thinking of adding weight to the buffer but trimming the extractor spring did it. now that I can fire enough rounds to check accuracy without torture of jamming it shoots 1/2 inch
 
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 un-happy 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 nesesity 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 disernable 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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Oh, price, I thank you for the link. A search didn't produce the O-Ring for me and I fully intent to pick one up regardless of immediate need or not.
 
i had missed that you had an adjustable gas block. so that still doesn't make sense to me as full-open on the gas should be limited by the port size in the barrel, which should be the 'standard' and still not 'overgassed'. especially on a midlength. if you ever take the thing apart, it would be interesting to measure the size of the port and see if it is normal or super-huge or something.
 
I am glad you have the rifle working right. Maybe you should think about taking off the adjustable gas system and put a standard one on seems like there would be less trouble. well enjoy it now
 
Yeah, I really haven't processed much of the science of it yet but I will. I have indeed been told on numerous occasions that a heavier buffer weight is needed in a mid length mid gassed barrel and that an adjustable gas block would do some of the same thing. I will divulge if things become clearer to me.
 
Knights, I don't. Not that I have specifically put into practice. Right now I have gummed it up with blue loctite but I don't know if that will be the end answer. There are ways. I don't actually recall how tight the screw was when I bought it but I don't think JP Enterprises had anything in there for the purpose either.
A favorite is screw against screw.
 
Don't get too carried away with the Loc Tite, especially on fine threads. Ask me how I know. ;)
 
Mohave I think you overestimated the carbine-middy under gas over gas puzzle that all the guys that think ARs are infallible say you must drive yourself crazy over. you have overthought a problem that would not have existed unless you tried to fix non existent problem with a complicated gas system that made your problem. it is a great gun you have and it will be accurate.if you have the time and money put on a standard system and stop listening to the AR fanatics lol
 
I just got done reading this thread and the first thought that came to my mind is that the gun is overgassed.

By no means am I an expert but I have been playing with ARs for over 20 years in one form or another.

There are quite a few manufactures that ship ARs and barrels with large gas ports to deal with folks that like to run the cheap steel cased ammo which is typically is loaded light. This higher amount of gas will insure that the bolt will still cycle.

The other issue you may be having is the fact that the barrel is an 18" with a midlength gas system. This is the same issue that people see with carbine length systems. The carbine system was designed around a 14.5" barrel but the barrels ended up being lengthened to 16" for civilian use. This can affect bolt dwell time because the bullet is in the barrel a little bit longer after it passes the gas port keeping the chamber pressure up, and making it harder for the bolt to extract the case.
 
Slightly off topic, (and the issue seems resolved, anyway) But I have that same barrel, and I love it.

_DSC9157.jpg

Mine has been flawless with a rifle length stock, and standard (rifle) DPMS Spring and Buffer.
 
Glad you found the issue and fixed it. I just saw your thread but if I had seen it in the beginning, I would have told you to not even waste your time trying to find something wrong with your BCG. You purchased one of the finest most sought after BCG's on the market. I don't know if you noticed but did you see how dirty your BCG was when you first got it? BCM will test each and every BCG to the extreme. They don't just shoot one round and assume everything is fine. They shoot multiple rounds consisting of multiple pressures just to make sure everything is in working order.

Consumers know this and it's exactly why we pay more for a BCM BCG.



Sent from my SGH-T999 using Tapatalk 4 Beta
 
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