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Posted: 1/14/2009 8:52:42 AM EDT
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OK, ill try to post this correctly.......
Mellow greetings fellow ARFers. I have a problem with my AR15. I've read the FAQ, the List Rules, the Sample Post and the Glossary and couldn't find this exact problem. My AR15 is a 20" fluted (non chrome-lined) barrel, Bushmaster Predator, with a Bushnell 3 X 9 X 40 illuminated reticle scope ,vented tubular aluminum handguards, gas operated semi auto (no piston), with no muzzle break, 5.56 / .223 caliber, fixed buttstock, Hybrid SAAMI spec. chamber, and it's firing 2 rounds with one pull of the trigger (only after it has gotten warm) with factory Bushmaster 30 rd. round mags firing Winchester 55 gr. FMJ, Remington 50gr. JHP, and UMC 45 gr. JHP ammo. When I fire the bolt comes to the rear and the expended case is not left in the chamber. The next round in the magazine feeds normally . I've not tried replacing anything I've had the rifle 4 months and this is the first problem I've had with it. Please help me I really really love my AR and I've been told you guys are the best. Thanks in advance. Terry |
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I have checked everything I can think of.....all components of the FCG look to be in good working order. Could it be that the firing pin is near top of tolerance and the heat generated causes it to expand just enough to give too much detent, and in turn firing?
Also thought it may just be a round cooking off but if it is, it sure happens fast. Anyone......Anyone......Bueller........... |
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Hold the trigger back and cock the hammer on a empty rifle.
Now very slowly release the trigger. The disco should release the hammer just before the trigger goes to rest to the trigger sear. If the hammer slips off the trigger sear, and the hammer falls all the way during this test. Pull the FCG and start cleaning/checking for pieces of a blow primer below the trigger. Also, since you did not round count, need to know if this a rifle just being broken in, or if the rifle has seen at least 1K of rounds. Furthermore, need to know if the problem is only happening off the bench or if it happens when shot off the bench in a free stance as well. |
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Thanx for the reply Dano.
I tried the test you mentioned, and all seems to work as it should. The rifle is not completely broken in, Ive only put 160 rounds through it so far. The only shooting thats been done has been with sandbags under the forward grip/guard. This problem has only happened 3 or 4 times,and it isnt occuring every time i shoot. While I am not new to rifles, I AM new to the AR platform, and greatly appreciate the help. |
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Welcome to the site Terry.
If your fire control group is clean, there is no debris underneath it and the parts are not broken then you are probably bump firing the second round that fires. This usually happens when you are slowly pulling the trigger when shooting off the bench. The recoil of the shot pushes the rifle back a little and then your shoulder pushes the rifle forward a little, pushing the trigger into your stationary finger and touching off the next shot. The cure for this is to deliberately pull through on the trigger making sure you don't stop the squeeze when the shot fires. It is pretty common with new AR shooters, and lots of fun in some people's opinion when you dump a whole mag this way with proper [ tall] backstop. Google it on this forum for more info. |
| A worn disconnector will sometimes release the hammer and cause a delay slam fire (I just made that term up) when the weapon hits battery. It would take a pro-timer to determine the duration, but it could seem like a 2 round burst or a double tap depending upon about 100 factors. Also sometime a hammer or trigger pin working out may cause this. |
| I just went through this after putting in a Jard 2lb single stage trigger in my Bushmaster Varminter. I'm an old guy and don't want to play the bump firing game and it really got my attention. I called Jard the the gal the answered the phone said to adjust my disconnector until it almost touches. That didn't help and I called again. This time she gave me the phone number of Dean a Tech and he asked if I backed off 7/8 of an inch after adjusting the trigger sear engagement. I'm getting too old to remember so I reset it. Turned the sear ingagement to the right until the hammer dropped and then turned the allen wrench sear adjustment 7/8 of an inch counter colockwise. I just ended up shooting 30 rounds without any problems and much better trigger control then I had before. My AR-10 trigger spoiled me but this 2 lb trigger is wonderful. I don't know if you've got any aftermarket trigger in your gun but I thought this mighthelp. |
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The term SLAM FIRE is well known. A rifle with only 140 rounds fired should not do this. It is a sure sign of a rifle malfunction. Slamfires can also cause a catastrophic malfunction (Breech explosion). Another well known term. Due to a round going off out of the chamber. Could be bolt timing, the FCG,(fire control group) sticky firing pin due to a small bit of brass in the bolt, etc. Did you clean the rifle before you fired it for the first time?
Have it checked out by a qualified AR gunsmith or if it is under warranty, Send it in for a checkup. If this was an old SKS, or the like, I would say worn parts. But a new rifle? No Way...shouldn't happen....Even if you were bump firing, The disconnector should grab the hammer and then drop it to the sear and the firing pin should not hit the primer hard enough to pop it until the bolt is closed and locked. If you were holding the weapon loosly, It would just stovepipe. I can mag dump 30 rnds in my Bushy patrolman AR in 3 seconds, Sad to say, 2 seconds in my Keltec SU-16A. Empty the mag on my Kimber before you can say one thousand and one. Double taps are one thing. Slamfires are altoghther another, Do a Google search on Slamfires in semiauto rifles. |
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