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Posted: 11/22/2002 5:47:05 AM EDT
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I have a Bushmaster Dissipator with approximately 750 rounds fired through it. I sent the gun to Accuracy Speaks to have them install their single stage trigger and adjust same to no less than 4 lbs. No weapon malfunctions of any kind during the first 750 rounds. I went to a patrol carbine training class and, during the course, the gun began choking. First, it began to occasionally double (fire two rounds with one pull of the trigger). This occurred at random, with no particular pattern as to when it would occur. Then it started to fail to lock the slide back on the last round, would try to feed more than one live round into the chamber at one time (both rounds would be out of the magazine and wedged into the chamber entrance), and seemed to be cycling slower than usual (according to the instructors watching the firing). I disassembled the rifle and found that one of the carrier key screws has loosened slightly, so I tightened the screw and fired the rest of the course without a malfunction of any kind, including doubling. I then sent the rifle to Bushmaster and they re-torqued, restaked and sealed the gas system. My question concerns the doubling problem. I replaced the Accuracy Speaks trigger with the factory unit. I called Accuracy and was told to send them the gun again if the doubling continues and they'd take care of the problem. Is it possible that the gas leak could have caused the gun to double? Is it likely to happen again? Like I said, the gun hasn't doubled in 200 rounds or more since the gas leak was fixed. I cannot have a rifle that is going to occasionally double. Should I have Accuracy try to fix the trigger, should I sell the trigger and use the factory one, or what? Thanks for your help in advance. |
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No matter what your gun gun does with regard to gas pressure...high or low...only a mafunctioning fire control group can cause a double. Now, it may very well be that your new trigger system malfunctioned BECAUSE of the gas problem, but that, in and of itself, is just WRONG. end tha gun back to whoever botched the trigger job and have them make it right. And just the idea that they ewould say something stupid like "If it continues..." I have not yet met the AR that can mechancally repair itself. The guy sho made that statement is an idiot and dangerous as well. Send it back. Your gun is now unsafe. |
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Waldo is correct. All I have to add to that is that you probably won't get any more doubling problems. If my math is correct, you have 750 rounds with no malfunctions with the Accuracy Speaks trigger, plus the number of rounds shot during the class when the malfunction manifested itself, plus 200 rounds after having your gas leak fixed. So figuring approximately 400 rounds for your class, you have approximately 1350 rounds on the Accuracy Speaks trigger, is that about right? Unless you replaced the trigger with the factory unit for the last 200 rounds... I'm not clear on when you put the factory trigger back in... before or after the last 200 rounds? Anyway, it's highly doubtful the Accuracy Speaks trigger wore out in 1350 rounds. They're rock solid triggers, one of the best made out there, and they're not adjustable so a loose screw is not a concern. I don't know who you spoke to at Accuracy Speaks, but I can say with certainty that Derek Martin will stand behind his work. But still, I'm not convinced the AS trigger was the problem. I'd put the AS trigger back in and give it another try if I were you. |
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To clarify, I had the Accuracy Speaks trigger installed (by Accuracy Speaks) after maybe 300 or so rounds through the new rifle. Then I put another 800 or 900 rounds through the gun with the A.S. trigger before the malfunction occurred. After tightening the carrier screws in the field, I put another 200 rounds through the gun (still with the A.S. trigger) with no malfunctions. I put the factory trigger back in the rifle AFTER the class was over when I sent the gun to Bushmaster for repair of the gas system and have yet to fire a round since receiving it back. Also, A.S. has offered to fix the problem and will stand behind the product. I only wish the trigger had been installed correctly the first time so that I don't have to go through the aggravation and expense of sending it off once again. But it was always my understanding that no matter what the problem was with the gas system, there had to be a trigger problem for the gun to double. I think I'll probably send it back, however, as the A.S. trigger is so much more crisp and lighter than the factory unit. Thanks for your help. |
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You had two separte problems. The first was that the disconnector was not retaining the hammer and was releasing it when the carrier slammed home. The second problem was that the carrier key had come loose and causing a gas leak. This lead to slow ejections, and feeding problems due to short stroking. The two caused separate problems and must be corrected separately. The key has been corrected, so your cycling will be correct, but the new FCG/disconnector will still release the hammer on carrier impact(jolt) with the barrel. Chances are that with the rifle cycling strong/harder than when you had a gas leak, the rifle will double a lot more, due to the carrier/bolt returning with more force. Note: If the bolt came far enough back to strip a round,the carrier came far enough back to have the disconnector retain the hammer. The hammer was retained even with the short stroking, it was bounced from the disconnector when the bolt closing jolted it from the disconnector. |
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Not to disagree but is very rare to a have a double fire as the result of a disconnector failure. When the secondary sear fails to engage, the hammer follow the bolt and does not strike with enough energy to fire the round. As I posted in another thread, for training purposes we have a disconnector ground off so it does not capture the hammer during the reward travel of the bolt to demonstrate the result of a failed disconnector. We also use this arrangement to train on failure to fire drills. The primary sear engages each time the charging handle is cycled provided you do not have the trigger in the reward position. Also, if a disconnector failure would cause this condition there would be a lot of illegal full auto conversions by merely grinding off the sear. Again the most common reason for this type of double is trigger control. The shooter does not concentrate on trigger reset and "bounces" the trigger finger. Occasionally during recoil recovery, the weapon moving forward contacts the trigger causing the unintentional double. In this instance I can see if the author going from a stock AR trigger with a substantial amount of trigger take up to one with very little and inadvertently contacting the trigger. this is in no way criticism of the author. Having a fair amount of law enforcement tactical weapons training experience, we see this scenario fairly frequently and more often the not later in the day after the shooter begins to fatigue and begins to lose some concentration. the exact same thing happens with auto loading pistol students. |
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Interesting theory, dws1057. Makes sense, especially on a light single stage trigger with a short reset such as the Accuracy Speaks. One way to tell for sure... install the Accuracy Speaks trigger and perform a safety function check. If it fails, send it back to Derek Martin for repair. If it passes, try it with live fire. Load three rounds in the magazine to be safe. And pay attention to your trigger finger follow-through and deliberately let it reset. |
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Quoted: Again the most common reason for this type of double is trigger control. The shooter does not concentrate on trigger reset and "bounces" the trigger finger. Occasionally during recoil recovery, the weapon moving forward contacts the trigger causing the unintentional double. This would be a bad case of disconector release set point. If the disconnector is releasing just beyond the trigger break point, then the shoulder bump would occur. If the disconnector is retaining the hammer as the bolt closes, but is bounced/jarred from the retained position, due to lack/weak engagement or weak disconnector spring strength, this can cause the doubles. If the disconnector release is set way short of trigger rest, the disconnetor can release the hammer, and the hammer sear can glance off the trigger sear due to the trigger not being in the correct position(sear under the hammer with the correct amount of ledge to retain the hammer), when resetting the trigger for the second shot. Rule of thumb regarding disconnector tuning is that the disconnector should release the hammer just before end of trigger reset/rest. This will prevent the operator from flinching and causing a second shot. Furthermore, this prevents the disconnector from releasing the hammer before the trigger can return to the correct position to retain the hammer, once released from the disconnector . On a AR-15, if you grind down/remove the disconnector, the hammer will bind on the firing pin and prevent the bolt from closing. You can not get hammer follow threw using this method. This is a safety feature that is built into the AR-15 system. If you simple wanted to simulate hammer follow threw on a M-16, just pull the auto sear, place the weapon on auto, then replace the sear to bring the rifle back to working condition. This method will cause the rifle to have hammer follow down every second shot after re-cock, verse taking the chance of the disconnector slightly retaining the hammer and the bolt/carrier impact firing a unexspectied shot. Food for thought. |
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Dano: I agree with most of what you said and perhaps a little further explanation is appropriate. First you are completely correct that simply grinding the hook off the disconnector and/or the rear of the hammer will typically result in the bolt carrier binding as the result of tension from the upward pressure of the hammer on the bottom of the bolt as the bolt carrier moves forward. The training fire control group I referred to does not have a generic colt hammer. I believe the hammer is from a colt match trigger set which looks more like the "low mass" hammers than stock colt. Further, the top surface which contacts the bottom of the bolt carrier has been rounded off and enough material removed that the reward movement of the bolt rocks the hammer just enough to engage the primary sear-provided the trigger is released. The result is that if you charge the weapon with a full(more than one round) magazine and then press and hold the trigger, the weapon will fire one round and the bolt carrier will function normally but the hammer will follow the bolt. This set up is used exclusively to introduce and practice immediate action drills (Smack, Rack, Bang) With respect to the possible reason I offered for the double fire please consider the following: The tactical doctrine I was trained under and know teach says we always double tap unless there is a specific reason not to. The doctrine also says that whenever the weapon is on target in a tactical situation the finger is on the trigger with the slack out of the trigger. Commonly, shooters will smash/bounce the trigger during the controlled pairs. What we see is the student smashing the trigger to fire the first round, bouncing the finger completely off the trigger instead of using a controlled reset and then smash the trigger again. What occasionally happens then is the shooter follows through the second shot, they try to get back on the trigger and slack out while assessing the threat. (During the assessment they are still “on target” hence finger should be on the trigger, slack out.) This is where the unintentional discharge happens. Weapons is moving forward during follow through, finger is looking for that "slack out" position, a little to much movement of the trigger finger and or forward movement of the weapon result is unintentional discharge. In general I begin by looking at the most common causations first. My experience suggests that trigger control issues are the most common reason for these types of unintentional discharge. I would also still maintain that with respect to ARs it is very uncommon to get a discharge as the result of hammer follow. I completely agree that a release by the disconnector when the bolt returns to battery with the trigger pressed would result in a second round being fired. There is also the possibility that as S09 allowed the trigger to move forward the disconnector released properly but the primary sear failed to engage. I just think that with quality components and proper installation, the human factors are more likely the reason rather than mechanical failure. |
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Guys-- Thanks for all the advice. In an abundance of caution, I sent the lower and AS trigger off to Accuracy today with a letter explaining the situation and requested they re-install the trigger and make certain everything is as it should be to prevent doubling. Regarding the trigger control issue as being a possible cause, I suppose it is possible, and this was brought up in the carbine class as a possible source of the problem. However, keep in mind that this NEVER occurred in the first 750 rounds, though most of those rounds were from a bench. I would expect doubling to be more of a problem when firing from any position other than from a benchrest, but the gun was even doubling off a benchrest at the class, where movement of the rifle was all but eliminated. Who knows!? Thanks again for all of the helpful information. Since I had around $200 in the trigger/installation, I figured one more trip to Accuracy would be worth it. |
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Lots of good commentary, so I will add only one thing. Derrick Martin designed his Accuracy Speaks single stage trigger for to give better single stage trigger than can be obtained without significant mods to the issue trigger. In his book, he says that he uses his trigger (NRA High Power, Distinguished, All Gaurd Team) like a release trigger with its short reset. Folks that like it positively rave about it. And they will usually outlast several barrels. When I read the first note, I thought "milking the trigger". The trigger likely moves a small fraction of the standard one, and you are actually pulling it twice as the rifle moves on your shoulder in recoil. We used to see this in High Power frequently when folks were tuning M-1 and M-14 triggers with short reset. It appears that you need more reste than the factory amount. Derrick's shop can probably increase the reset for you. |
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Quoted: Dano: I believe the hammer is from a colt match trigger set which looks more like the "low mass" hammers than stock colt. Further, the top surface which contacts the bottom of the bolt carrier has been rounded off and enough material removed that the reward movement of the bolt rocks the hammer just enough to engage the primary sear-provided the trigger is released. The result is that if you charge the weapon with a full(more than one round) magazine and then press and hold the trigger, the weapon will fire one round and the bolt carrier will function normally but the hammer will follow the bolt. This set up is used exclusively to introduce and practice immediate action drills (Smack, Rack, Bang) FYI: This trick can get you charged with intent to create a Machine gun!!!!!!!! The sole reason that you can not use any M-16 parts in a AR-15, is that it is possible to create a machine gun by using the hammer follow method. Granted that a few of the "parts" would need to be out of spec for the rifle to run this way, but it would run. I will not post how to do it, but it was done in the past and the BATF no longer allows M-16 parts or "like configurations", because of people converting the rifles to run full auto, without using a auto sear. |
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