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Posted: 11/3/2012 4:44:51 AM EDT
| I have a NDS lower that I had built with a Colt 2 piece 9MM mag block and Colt 9MM long finger bolt catch. It will not hold the bolt open. I am running a Spikes ST-9X buffer and Wollf XP buffer spring in a 6 pos CAR stock. Any suggestions why it will not work? I have a std CMMG LPK and RRA 16" Mid length upper with a ramped bolt. The lower was built by a well know shop. I am using Colt factory 9MM mags and Metalform mags, no spacer in the buffer tube, It is not holding the bolt open on a empty mag. I cannot even manually activate the bolt catch with or without a mag in.I have another lower, a CMMG dedicated factory 9MM that works perfectly. What gives? |
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Is it not holding the bolt open on an empty mag? What mags are you using?
Can you activate the bolt hold open without a mag? What bolt catch do you have? Standard bolt catch or Colt long finger bolt catch? Do you have any spacers inside the buffer tube behind the buffer itself? |
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Do you have another lower, even in 5.56, to compare the overall movement of the BHO to? It sounds like maybe the recess for the BHO wasn't machined deep enough to allow it to swing fully up. It could also be a problem with the spring binding and not allowing full movement.
Take it apart and take a look at it. Maybe even put in a standard catch for testing and see if when you manually activate it (with your fingers that is), if it will hold the bolt back then. If even that does not, it is probably a lower issue. Then you can troubleshoot it from there, either modifying the lower slightly or the catch itself. Good luck and let us know when you find. Bitter Bastard |
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Problem may be the bolt hold open is the same height as a 5.56 bolt catch and barely catches the bolt so this may give you issues. If you compare it to your CMMG dedicated 9mm lower you will see it is taller and catches the bolt with no problem.
I have the same issue and I have two 9mm AR's, one is an older CMMG that uses a Hahn dedicated block and with a standard 5.56 bolt catch, the other is built on a CMMG dedicated 9mm lower with a 9mm bolt catch. This is the dedicated 9mm lower, a little hard to tell but if you notice the bolt catch is taller than the one pictured below, I'm going to guess that your bolt catch in the lower that's giving you problems is shorter. 
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| I do not believe it is a mag catch problem, it works perfectly after I removed the Spikes ST-9X buffer and Wolff XP spring and swapped it for a RRA 9MM std buffer and std buffer spring. It is a NDS lower with a 6 pos CAR buffer tube and a RRA 16" mid length upper with a ramped bolt, std CMMG 5.56 LPK in the lower except for the Colt 9MM extended bolt catch. I think the Spikes extended buffer is too long. I am not using any spacers in the buffer tube.I have another 9MM lower set up- a CMMG dedicated factory 9MM lower with 6 pos CAR buffer tube with a std buffer spring and a Spikes ST-9X extended length buffer with no spacers, using the same RRA 16" upper and it locks the bolt back first time, every time. Maybe it is the Wolff XP spring that is the problem? |
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Quoted:
I do not believe it is a mag catch problem, it works perfectly after I removed the Spikes ST-9X buffer and Wolff XP spring and swapped it for a RRA 9MM std buffer and std buffer spring. It is a NDS lower with a 6 pos CAR buffer tube and a RRA 16" mid length upper with a ramped bolt, std CMMG 5.56 LPK in the lower except for the Colt 9MM extended bolt catch. I think the Spikes extended buffer is too long. I am not using any spacers in the buffer tube.I have another 9MM lower set up- a CMMG dedicated factory 9MM lower with 6 pos CAR buffer tube with a std buffer spring and a Spikes ST-9X extended length buffer with no spacers, using the same RRA 16" upper and it locks the bolt back first time, every time. Maybe it is the Wolff XP spring that is the problem? Most likely the problem is with the Wolff XP action spring. Combination of a very heavy buffer and spring. |
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Quoted:
I do not believe it is a mag catch problem, it works perfectly after I removed the Spikes ST-9X buffer and Wolff XP spring and swapped it for a RRA 9MM std buffer and std buffer spring. It is a NDS lower with a 6 pos CAR buffer tube and a RRA 16" mid length upper with a ramped bolt, std CMMG 5.56 LPK in the lower except for the Colt 9MM extended bolt catch. I think the Spikes extended buffer is too long. I am not using any spacers in the buffer tube.I have another 9MM lower set up- a CMMG dedicated factory 9MM lower with 6 pos CAR buffer tube with a std buffer spring and a Spikes ST-9X extended length buffer with no spacers, using the same RRA 16" upper and it locks the bolt back first time, every time. Maybe it is the Wolff XP spring that is the problem? Well then I'm going to say the Wolff XP spring is your issue, may be to long and not allowing the ST-9X buffer to go back far enough. I have ST-9X buffers in mine with a standard CAR springs and have no issues. |
| I have tried every single combo of spring and buffer that I could except using a spacer so far and the only combo that works is the 5.6oz RRA 9MM buffer with a standard CAR spring. It locks the bolt back every time. I am worried that my bolt is going back too far and battering my lower so I have a Spikes 9MM buffer spacer coming. If that doesn't work, I will try the quarter trick. I even checked the buffer tube to see if I could turn it out or in one thread-it is optimal in only one position so that is not the problem. I am really discouraged because I wanted to use the Spikes ST-9X buffer to protect my lower. I do have KNS hammer/trigger pins on the lower though.I do not want to break my Colt 9MM bolt catch. |
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