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Posted: 6/14/2010 5:52:06 AM EDT
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Just thought I would post this to see what you guys think. I am doing a sbr in 9mm (it is in pistol form right now). The upper is a 10.5 inch rock river and the mag block is rock river as well. I purchased the upper used and found out later that it didnt have a firing pin spring in it. It now does. The lower is a spikes that has a rock river parts kit in it with a 9mm hammer. It also has the heavier 9mm bufer in it. From what I can tell, the bolt is not ramped.
So here is my issue. Manually, the gun cycles and functions great. Trigger resets as it is supposed to. However, when I took it out yesterday to test a magfull, I pulled the trigger and low and behold 3 round burst. Tried again and still fully auto. I had to try it one more time  just to make sure it wasn't a fluke. Yep full auto again. So any ideas what might be causing this??? For whatever reason, the hammer keeps falling as long as you hold the trigger down. Any help would be greatly appreciated.
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Weak handloaded ammo or to heavy of a buffer or spring or both or trigger group problems.
If you put one round in a mag and shoot it does the bolt hold back ? sounds like its short stroking because the bolt isn't coming back far enough to cock the hammer and hold. |
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Weak handloaded ammo or to heavy of a buffer or spring or both or trigger group problems. If you put one round in a mag and shoot it does the bolt hold back ? sounds like its short stroking because the bolt isn't coming back far enough to cock the hammer and hold. +1 Check all these things. Bad thing about used parts, you are never 100% sure of what you have. Heck, sometimes even with new parts that is a problem! Check that FCG, as in trigger and sear, real close. Use good full power factory ammo to test. I normally just put in three rounds or so for a new weapon until I am sure it is going to function properly. You know why! |
| May also want to check your disconnector. Did you do a proper function check before firing and check over parts to eliminate things like a stuck firing pin? I know a weak or incorrect FPS in Oly's can cause bursting, but have never seen or experienced it myself with Colt style guns. |
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Another vote for disconnect hook engagement to the hammer shelf... 9 mm has a little more "thud" about it that can shake a minimal engaged disconnect hook to hammer off the shelf and let it run.. been there..
Re-time/fit the disconnect claw for deeper engagement to shelf on the hammer... should take you no more than 15 minute if you understand what to do. |
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Here is some more info based on questions/suggestions Ammo was winchester white box Firing pin is not sticking when pushed or hit by hammer Fire one round and see if the bolt comes back far enough to recock the hammer and lock the bolt back, if it does then start looking at the trigger group for problems. |
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Here is some more info based on questions/suggestions Ammo was winchester white box Firing pin is not sticking when pushed or hit by hammer Fire one round and see if the bolt comes back far enough to recock the hammer and lock the bolt back, if it does then start looking at the trigger group for problems. I would suggest going back and inspecting all parts first (make sure the previous owner didn't mod them) and doing a proper function check before firing any more rounds...if the disconnector or other fire control parts are not not interacting properly, there is a high likelihood that will show up in a proper function check...just my 2 cents though, so take it for what it's worth... |
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Ok...so I have done a little research and inspected the pistol a little more. The function check on the trigger is fine. I can manually cycle the bolt and everything works as it should including the disconnector. My opinion (and thats all it is ) is that the disconnector is not engaging the hamer well enough to keep the hammer from falling when the bolt cycles and thumps forward. I have a spare disconnector that I can try, but would like to know how to improve the current one.
To get better engagement of the disconnector to the hammer what do I do??? Do I increase the angle of the face of the disconnector??? I assume this is the same as re- working the timing of the disconnector/hammer interface. Any other help would be appreciated. Thanks for all of the replies to date. |
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Ok...so I have done a little research and inspected the pistol a little more. The function check on the trigger is fine. I can manually cycle the bolt and everything works as it should including the disconnector. My opinion (and thats all it is ) is that the disconnector is not engaging the hamer well enough to keep the hammer from falling when the bolt cycles and thumps forward. I have a spare disconnector that I can try, but would like to know how to improve the current one.
To get better engagement of the disconnector to the hammer what do I do??? Do I increase the angle of the face of the disconnector??? I assume this is the same as re- working the timing of the disconnector/hammer interface. Any other help would be appreciated. Thanks for all of the replies to date. To get the disconnector to engage the hammer better you could lightly file the BOTTOM FRONT of the disconnector-that's the part that touches the front part of the trigger. Lightly is important here, because if you take off too much material you could wind up keeping the hammer from transferring to the trigger's sear. But a disconnector is like $5. How much dinking around do you want to do on a $5 part, versus tossing in a new one and being able to go to the range safely? |
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Ok...so I have done a little research and inspected the pistol a little more. The function check on the trigger is fine. I can manually cycle the bolt and everything works as it should including the disconnector. My opinion (and thats all it is ) is that the disconnector is not engaging the hamer well enough to keep the hammer from falling when the bolt cycles and thumps forward. I have a spare disconnector that I can try, but would like to know how to improve the current one.
To get better engagement of the disconnector to the hammer what do I do??? Do I increase the angle of the face of the disconnector??? I assume this is the same as re- working the timing of the disconnector/hammer interface. Any other help would be appreciated. Thanks for all of the replies to date. To get the disconnector to engage the hammer better you could lightly file the BOTTOM FRONT of the disconnector-that's the part that touches the front part of the trigger. Lightly is important here, because if you take off too much material you could wind up keeping the hammer from transferring to the trigger's sear. But a disconnector is like $5. How much dinking around do you want to do on a $5 part, versus tossing in a new one and being able to go to the range safely? I don't recommend messing with any of that. These parts are dirt cheap, and if you end up being in public, and the same thing happens in front of the long arm of the law, you could be in hot water when they find a disconnector that has been screwed with. If it was me, I'd be replacing the whole trigger and hammer (with small parts), and hope it goes away. |
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Ok...so I have done a little research and inspected the pistol a little more. The function check on the trigger is fine. I can manually cycle the bolt and everything works as it should including the disconnector. My opinion (and thats all it is ) is that the disconnector is not engaging the hamer well enough to keep the hammer from falling when the bolt cycles and thumps forward. I have a spare disconnector that I can try, but would like to know how to improve the current one.
To get better engagement of the disconnector to the hammer what do I do??? Do I increase the angle of the face of the disconnector??? I assume this is the same as re- working the timing of the disconnector/hammer interface. Any other help would be appreciated. Thanks for all of the replies to date. To get the disconnector to engage the hammer better you could lightly file the BOTTOM FRONT of the disconnector-that's the part that touches the front part of the trigger. Lightly is important here, because if you take off too much material you could wind up keeping the hammer from transferring to the trigger's sear. But a disconnector is like $5. How much dinking around do you want to do on a $5 part, versus tossing in a new one and being able to go to the range safely? I don't recommend messing with any of that. These parts are dirt cheap, and if you end up being in public, and the same thing happens in front of the long arm of the law, you could be in hot water when they find a disconnector that has been screwed with. If it was me, I'd be replacing the whole trigger and hammer (with small parts), and hope it goes away. Using that logic, it would be unwise to buy anything but factory assembled guns and if they ever required work, one should simply replace parts, rather than fix them so they can show "the long arm of the law" that they were never modified... There is nothing wrong with modding FCG parts so they function properly, as long as the person knows what they are doing. It is not uncommon to have to mod a disconnector due to tolerances within various parts and tolerance stack of all parts when assembled. As for the OP, if you cycle the action, pull the trigger and hold it, then pull the charging handle back and let it fly, can you get the hammer to come off the disconnector? If it is barely engaging, letting the bolt fly should be enough to get it to drop off the disconnector. You should also be able to visually check how much contact there is between the hammer and disconnector and compare it to another known good lower - then modify from there to increase the contact between the disco and the hammer until it stops bursting. |
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Ok...so I have done a little research and inspected the pistol a little more. The function check on the trigger is fine. I can manually cycle the bolt and everything works as it should including the disconnector. My opinion (and thats all it is ) is that the disconnector is not engaging the hamer well enough to keep the hammer from falling when the bolt cycles and thumps forward. I have a spare disconnector that I can try, but would like to know how to improve the current one.
To get better engagement of the disconnector to the hammer what do I do??? Do I increase the angle of the face of the disconnector??? I assume this is the same as re- working the timing of the disconnector/hammer interface. Any other help would be appreciated. Thanks for all of the replies to date. To get the disconnector to engage the hammer better you could lightly file the BOTTOM FRONT of the disconnector-that's the part that touches the front part of the trigger. Lightly is important here, because if you take off too much material you could wind up keeping the hammer from transferring to the trigger's sear. But a disconnector is like $5. How much dinking around do you want to do on a $5 part, versus tossing in a new one and being able to go to the range safely? I don't recommend messing with any of that. These parts are dirt cheap, and if you end up being in public, and the same thing happens in front of the long arm of the law, you could be in hot water when they find a disconnector that has been screwed with. If it was me, I'd be replacing the whole trigger and hammer (with small parts), and hope it goes away. Using that logic, it would be unwise to buy anything but factory assembled guns and if they ever required work, one should simply replace parts, rather than fix them so they can show "the long arm of the law" that they were never modified... There is nothing wrong with modding FCG parts so they function properly, as long as the person knows what they are doing. It is not uncommon to have to mod a disconnector due to tolerances within various parts and tolerance stack of all parts when assembled. As for the OP, if you cycle the action, pull the trigger and hold it, then pull the charging handle back and let it fly, can you get the hammer to come off the disconnector? If it is barely engaging, letting the bolt fly should be enough to get it to drop off the disconnector. You should also be able to visually check how much contact there is between the hammer and disconnector and compare it to another known good lower - then modify from there to increase the contact between the disco and the hammer until it stops bursting. Your analogy is more than a stretch from my recommendation. If I had a gun that was running full auto, and the probable defective part is only $5, and readily available, yes I would swap it out as apposed to modding it. That is pretty damn far away from only buying assembled guns. There's no point in ridiculing someone's opinion. |
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Your analogy is more than a stretch from my recommendation. If I had a gun that was running full auto, and the probable defective part is only $5, and readily available, yes I would swap it out as apposed to modding it. That is pretty damn far away from only buying assembled guns. There's no point in ridiculing someone's opinion. Fact is, if a gun goes full auto whether you did anything to it or not, "johnny law", can make your life miserable. My commentary was pretty much spot on and I don't believe it was ridiculing you in the least. My apologies that you don't agree, but such is life. Many people don't agree with me, but I don't complain that they are ridiculing me simply because their comments differ from mine... Although AR's as as easy to assemble as most Lego kits (perhaps easier than most), it doesn't mean they will all run 100% as is. If you build enough, it is not uncommon to have to tweak things here or there. Tweaking a disconnector to make sure the FCG is 100% is not a big deal and is just a part of the process sometimes. There's no guarantee that a replacement disconnector will be any better or solve the problem either. So, it may not be as simple as just replacing a $5 part. It's kind of like the old analogy - give a man a fish and he eats for a day, teach a man to fish and he eats for a lifetime... It is a 5-10 minute job to visually verify that the FCG is properly functioning and tweak the disconnector to ensure proper/reliable engagement (if necessary). |
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Ok...so I have done a little research and inspected the pistol a little more. The function check on the trigger is fine. I can manually cycle the bolt and everything works as it should including the disconnector. My opinion (and thats all it is ) is that the disconnector is not engaging the hamer well enough to keep the hammer from falling when the bolt cycles and thumps forward. I have a spare disconnector that I can try, but would like to know how to improve the current one.
To get better engagement of the disconnector to the hammer what do I do??? Do I increase the angle of the face of the disconnector??? I assume this is the same as re- working the timing of the disconnector/hammer interface. Any other help would be appreciated. Thanks for all of the replies to date. To get the disconnector to engage the hammer better you could lightly file the BOTTOM FRONT of the disconnector-that's the part that touches the front part of the trigger. Lightly is important here, because if you take off too much material you could wind up keeping the hammer from transferring to the trigger's sear. But a disconnector is like $5. How much dinking around do you want to do on a $5 part, versus tossing in a new one and being able to go to the range safely? I don't recommend messing with any of that. These parts are dirt cheap, and if you end up being in public, and the same thing happens in front of the long arm of the law, you could be in hot water when they find a disconnector that has been screwed with. If it was me, I'd be replacing the whole trigger and hammer (with small parts), and hope it goes away. Using that logic, it would be unwise to buy anything but factory assembled guns and if they ever required work, one should simply replace parts, rather than fix them so they can show "the long arm of the law" that they were never modified... There is nothing wrong with modding FCG parts so they function properly, as long as the person knows what they are doing. It is not uncommon to have to mod a disconnector due to tolerances within various parts and tolerance stack of all parts when assembled. As for the OP, if you cycle the action, pull the trigger and hold it, then pull the charging handle back and let it fly, can you get the hammer to come off the disconnector? If it is barely engaging, letting the bolt fly should be enough to get it to drop off the disconnector. You should also be able to visually check how much contact there is between the hammer and disconnector and compare it to another known good lower - then modify from there to increase the contact between the disco and the hammer until it stops bursting. First of all, many thanks to all that have replied as the troubleshooting help and opinions are much appreciated. However, I am in the camp that if I can figure this thing out on my own, I can troubleshoot future builds on my own. Hence, I will continue to fiddle with the current parts in the pistol until I can figure out what is causing the failure. I have spare parts laying around that I can swap in and out, and if I cant figure out what is wrong with the current configuration, I will swap one part at a time until it is correct. So, last night I did more function checks with the trigger group and I can not get it to fail no matter what I do. I can't get the hammer to fall off of the disconnector no matter what I do manually even pushing on it with my finger. I can cycle the action vigorously and the disconnector holds?WTF? I do still believe that the malfunction when firing is in the trigger group. The last time I fired the pistol, i put two rounds in the mag and the bolt did hold open, so I dont believe the bolt is short stroking. The only other thing I can think that could be causing the issue is a weak firing pin spring. The spring is brand new and is the correct part. I will probably tinker with it this weekend, so any guidance as a next step would be much appreciated. Thanks in advance. |
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If it is always bursting 3 rounds, you may need to catch it in the act to find out what is going on. I would disable the bolt catch or use a modded Uzi mag so the bolt won't lock back on an empty mag. I would load the mag with 2 rounds, pull the trigger and hold it back. Once both rounds fired, I would check and see whether the disconnector caught the hammer or not. If the engagement is minimal or the disconnector spring is weak, the recoil could be allowing the hammer to drop when it shouldn't.
If the disconnector is catching the hammer properly, then you may be back to the bolt - bad/incorrect firing pin spring or bad firing pin? |
| Ok...couldnt stand it anymore. Took the hammer out and compared it side by side with the 223 hammer I have. The disconnector engagement surface is a totally diferent angle and the hammer just didnt look right to me compared to the other. I am talking about the backside of the hammer where it engages the disconnector. Anyway, swapped out the hammer and bingo...semi-auto. I still need to grind the back of the hammer down to make it compatible with the 9mm bolt, but I am glad to find out, it was the hammer to disconnector engagement that was causing the problems. After I thought about it a while and talked to every resource I could find including a tech at rock river, I got thinking that the only part I really didn't know the origin of was the hammer. I picked it up at the last gun show I went to. Not sure if it is out of spec or not, but it is definitely different at the disconnector engagement surface. I will get a couple pics up of the two different hammers when I get a chance, and thanks again for all of the responses and help. I couldn't have gotten to the point that I did without this forum or all of the suggestions provided. Thanks again. |
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Ok...couldnt stand it anymore. Took the hammer out and compared it side by side with the 223 hammer I have. The disconnector engagement surface is a totally diferent angle and the hammer just didnt look right to me compared to the other. I am talking about the backside of the hammer where it engages the disconnector. Anyway, swapped out the hammer and bingo...semi-auto. I still need to grind the back of the hammer down to make it compatible with the 9mm bolt, but I am glad to find out, it was the hammer to disconnector engagement that was causing the problems. After I thought about it a while and talked to every resource I could find including a tech at rock river, I got thinking that the only part I really didn't know the origin of was the hammer. I picked it up at the last gun show I went to. Not sure if it is out of spec or not, but it is definitely different at the disconnector engagement surface. I will get a couple pics up of the two different hammers when I get a chance, and thanks again for all of the responses and help. I couldn't have gotten to the point that I did without this forum or all of the suggestions provided. Thanks again. You can put in a rounded .223 hammer and just go with it... 
That weird-ass "9mm hammer" is ONLY compatible with 9mm bolts, while the rounded hammer is compatible with almost everything. 
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