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Posted: 2/6/2010 9:01:57 PM EDT
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I just finished my build and went to shoot it. I fire a shot and the bolt cycles, throws out the spent case, then closes on an empty chamber. This is a consistent problem the gun is brand new. Has not worked properly yet.
Rifle is a RR Lower, YH Upper, 16" Adams Arms Barrel, YHM NM bolt and Bolt Carrier, Vltor stock, DD rail, BWA muzzle brake, RR trigger SS trigger, low pro gas block Here is what I tried: 1) 4 different high quality magazines (still won't work) 2) Re-installed the gas block to be sure it is centered over the gas port in the bbl (still no good) 3) Threw in a Bushmaster bolt/carrier (did the same thing) 4) Tried a Bushmaster lower on my upper (same problem) 5) Tried the Bushmaster upper on my lower (worked fine) Conclusion??? 
The problem has to be in my upper, can't be my bolt, carrier or gas key because they worked in the Bushmaster. Can't be in my lower because it worked with the Bushmaster upper. So I conclude it's in the gas block and/or gas tube. Took them off and they look fine no obvious pinch, can't really see down the tube. Any ideas what it could be???
Todd |
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First off, Welcome to the site!!!!
Now lets get to it, Rig fully cleaned and CLP lubed from the beginning? If you have to ask if you did this correctly, then thecleaning forum can cover you on how to do this correctly. Ammo, are you using brass case factory ammo, or trying to break the rifle in with coated ammo/reloads? Bolt out of the carrier, and using the carrier alone in the upper receiver, is the gas tube aligned with the carrier key, or is there binding as the tube enters the key. On the same note, does the carrier alone glide in the upper receiver, or is the key too wide for the upper receiver slot. More on binding, as you go to cock the rifle empty, is the charging handle pull from about the center to the back of the pull about the same tension, or does the tension increase about the last few inches? Gas system, you stated that you have reset the gas block. Is the block to the barrel a tight fit or not. Also, did you confirm that the gas tube was installed correctly to the block and you have flow through not only the tube and block alone, but also flow through tube when the block is mounted to the barrel (though to the bore) without major leaks. Barrel, have you confirmed head space? Also have you checked the condition of the chamber (smooth as a babies ass with no chamber reamer chatter). If a head space gauge is not available, then you can semi check such with a live round. Upper alone, drop a live round into the chamber, tap the back of the round with a wooden dowel to make sure the round is all the way forward, then aim the muzzle straight up. The round should fall back out of the chamber. Now put the upper back on the lower, drop a live round into the chamber, now walk the bolt forward with charging handle, and lightly use the forward assist to seat the bolt home. Does it only take a light press of the forward assist to lock the bolt, or do you have to stab hard on the FA to get the bolt to lock home. Also, when you go to unlock the bolt/remove the live round, is the pull back on the charging handle easy, or are you have to really go after the handle to unlock the bolt. Really, the devil is in the details, and if this is your first AR, it may help to have someone local take a look at the build. It doesn't need to be a full blown smith, and if needed, you can post in the home town forum to see if anyone around you could give the rifle a once over. It could be any of the above problem, of something even more simple as something in the build just quit not right. |
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Thank you for the welcome and the answers.
I did fully clean a lube the gun before shooting and repeated the process after discovering the problem. Also its a standard gas impingement system not a piston sytem. Ok now answer to questions people asked me: 1) I was shooting mostly Winchester white box 55 grain fmj no coating used 2) Looks like the gas block is/was set propoerly centered over the gas port in the barrel. I think it is tight enough. The little gas "stain" around the port loooks centered 3) I inspected the gas tube and block off the barrel and put a little allen key in to see if there was an obstruction in the entrsnce hole of the tube. 4) Took the tube off the gas block to inspect it and it looks right to me 5) Buffer is a standard mil spec buffer and spring. How would I know if there are major leaks in the gas block/tube assembly? How do I know if the gas block it tight to the barrel? Then how do I test the gas flow is correct? I will do the suggested headspace test, and the others. I think I'm gonna have to bring it to a local smith. I wanted to figure it out myslef but oh well. I am convinced that its a gas system problem localized to the tube and block becaue the Bushmaster carrier and bolt malfuntioned similarly. TR |
I had the same problem. Tried a new carrier key and gas tube on my 16" upper and still short stroked. I knew it had to be a gas problem so I removed the front sight base and checked the spacing for the gas hole in the barrel and the hole in the sight base, the barrel was miss drilled from the factory. Ive never run across this before in over twenty years of building ARs. I replaced the barrel with one by DEZ and the problem was fixed.
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I had similar problems and went through all the standard things looking into the gas system, assembly, buffer, buffer spring. Then I spoke with the armorer at Alexander Arms (not Bill Alexander, but someone else). He suggested changing the gas rings. They looked fine to me, but I though "Why not, they are cheap, and it will be another variable to cross of the 'have you tried' list".
The new gas rings fixed every thing. I kept the old rings and they still look perfect. For some reason, they weren't holding enough pressure though. But now it works. Good luck, and as others have said, Welcome to the forum. |
| Ran into a similar problem with a new build a couple weeks ago. Long story short, the gas hole in the barrel was a little on the small side. I drilled it to .063 (which Colt says is spec for a carbine gas system) and put it all back together. Put a bout 400rds through her last Sunday without a hitch. Just some food for thought. |
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