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Posted: 4/1/2012 4:46:56 PM EDT
[#1]
Quoted:
Everything is making a lot more sense to me now, unless Bushmaster has discovered a magic secret o n how else to resist the pressures of the 7.62 NATO/.308 in carbines with a 3.6oz buffer. In your gun, they obviously did not. 3.6oz buffer weight in any AR10 cahmbered in a cartridge with 40.0-47.0+ grains of powder, common gas system lengths, and common gas port diameters is simply not enough. You need a buffer that is at least 5.4oz, and I suspect you will see these issues go away with the CAR-10 buffer and new bolt. When you look at the impact mark your cam pin made on the upper, you can see that there was nowhere near enough mass resistance to slow down the violent rearward movement of the BCG, and this violent cycling likely caused that impact mark, as well as the damage to your bolt lugs. That is my best guess what was going on with your system. I have run insane over-pressure loads during load development (never continued them of course) in my .260 Rem AR10 with DPMS BCG, with a DPMS rifle buffer, and never seen anything like that. The cam pin rotates into the receased area when the bolt closes, not when it opens |
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Posted: 4/1/2012 6:04:27 PM EDT
[#2]
Quoted:
Quoted:
Everything is making a lot more sense to me now, unless Bushmaster has discovered a magic secret o n how else to resist the pressures of the 7.62 NATO/.308 in carbines with a 3.6oz buffer. In your gun, they obviously did not. 3.6oz buffer weight in any AR10 cahmbered in a cartridge with 40.0-47.0+ grains of powder, common gas system lengths, and common gas port diameters is simply not enough. You need a buffer that is at least 5.4oz, and I suspect you will see these issues go away with the CAR-10 buffer and new bolt. When you look at the impact mark your cam pin made on the upper, you can see that there was nowhere near enough mass resistance to slow down the violent rearward movement of the BCG, and this violent cycling likely caused that impact mark, as well as the damage to your bolt lugs. That is my best guess what was going on with your system. I have run insane over-pressure loads during load development (never continued them of course) in my .260 Rem AR10 with DPMS BCG, with a DPMS rifle buffer, and never seen anything like that. The cam pin rotates into the receased area when the bolt closes, not when it opens If that is true, then what turns the bolt to unlock it? isnt it just opposite rotation? |
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Posted: 4/1/2012 6:39:16 PM EDT
[#3]
Quoted:
Quoted:
Quoted:
Everything is making a lot more sense to me now, unless Bushmaster has discovered a magic secret o n how else to resist the pressures of the 7.62 NATO/.308 in carbines with a 3.6oz buffer. In your gun, they obviously did not. 3.6oz buffer weight in any AR10 cahmbered in a cartridge with 40.0-47.0+ grains of powder, common gas system lengths, and common gas port diameters is simply not enough. You need a buffer that is at least 5.4oz, and I suspect you will see these issues go away with the CAR-10 buffer and new bolt. When you look at the impact mark your cam pin made on the upper, you can see that there was nowhere near enough mass resistance to slow down the violent rearward movement of the BCG, and this violent cycling likely caused that impact mark, as well as the damage to your bolt lugs. That is my best guess what was going on with your system. I have run insane over-pressure loads during load development (never continued them of course) in my .260 Rem AR10 with DPMS BCG, with a DPMS rifle buffer, and never seen anything like that. The cam pin rotates into the receased area when the bolt closes, not when it opens If that is true, then what turns the bolt to unlock it? isnt it just opposite rotation? The bolt carrier traveling to the rear makes the cam pin rotate to the center position unlocking the bolt. |
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Posted: 4/1/2012 9:11:35 PM EDT
[#4]
Roger that to all the above. Lighter weight buffer = faster cycling of the action, which not only can be violent on unlocking, but the return stroke and locking as well. I'm not sure if that was doing it, or if it was something with the dimesnions being out of spec, but I haven't seen that slit mark from the cam pin in the cam pin recess in the upper before.
It's telling that the manufacturer didn't fix it either. |
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Posted: 4/1/2012 9:20:15 PM EDT
[#5]
Thanks for clarification.
Is it possible for the carrier to be mismachined, causing the cam pin to prevent the bolt from locking completely? |
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Posted: 4/15/2012 6:21:55 PM EDT
[#6]
is this common to all the bushys or just a rare inciudent ?i am interested in buying one of these but don't want to buy into issues
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Posted: 4/15/2012 8:45:46 PM EDT
[#7]
I picked up one of the ORC's when Sportsmans had them for $799 which has about 500-600 rounds down the tube and shows no signs of odd wear as described here. I changed out the handguard and upgraded the stock to a CTR but other than that the rifle is stock and seeing as these have nothing to do with the function of the rifle I'm either lucky or this guys is unlucky
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Posted: 5/14/2012 5:02:34 PM EDT
[#8]
I'm no expert, but I would say the 'pinging' on the back side of the locking lugs occurs on bolt closing, not opening.
When the AR bolt closes, they 'bounce' off the breach-face and start to turn as the lock up. Since the bolt is not under spring pressure (only the carrier is) the bolt is free to bounce back and ding into the barrel lugs before the carrier continues to close and forces the completion of the turn. Not sure what long term problems this may cause, if any. Since the 308 bolt is considerably heavier than the 223 bolt, the 'bounce' would certainly be more pronounced. Not saying the problem is 'normal', but I'm curious to learn if the issue becomes pronounced or effects reliability in the long run. |
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Posted: 5/15/2012 8:06:51 AM EDT
[#9]
Probably beaten to death already, but....
Pics of a new out of the box Bushmaster MOE .308 carbine–– 
Note the lack of attention to detail on the ejector pin hole: 
Note the gash from the cam pin: 
Let's see if this will help: 
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Posted: 5/15/2012 8:45:30 AM EDT
[#10]
Quoted:
I'm no expert, but I would say the 'pinging' on the back side of the locking lugs occurs on bolt closing, not opening. When the AR bolt closes, they 'bounce' off the breach-face and start to turn as the lock up. Since the bolt is not under spring pressure (only the carrier is) the bolt is free to bounce back and ding into the barrel lugs before the carrier continues to close and forces the completion of the turn. Not sure what long term problems this may cause, if any. Since the 308 bolt is considerably heavier than the 223 bolt, the 'bounce' would certainly be more pronounced. Not saying the problem is 'normal', but I'm curious to learn if the issue becomes pronounced or effects reliability in the long run. I agree. The damaged lugs on the OP's bolt is caused by bolt bounce when closing. All ones needs to do is look at how the bolt rotates in to the barrel extension as it closes. I can't say about the BM RE and buffer, but I do know that DPMS RE's (consolable) are AR15 length, use a modified (shortened) AR15 buffer. Where as ArmaLite, KAC, Noveske, LMT, and CMMG all use a RE (consolable) that is a half inch longer to compensate for the longer .308 bolt. Just over 1K in my Noveske N6 and the back of the lugs are just starting to wear the finish. |
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Posted: 5/15/2012 1:01:27 PM EDT
[#11]
WOW!
This is NIB? Have you tried to load a round in the chamber, if you have how dificult is it to manually eject? Quoted:
Probably beaten to death already, but.... Pics of a new out of the box Bushmaster MOE .308 carbine–– http://i29.photobucket.com/albums/c256/arfcompics/007-2.jpg Note the lack of attention to detail on the ejector pin hole: http://i29.photobucket.com/albums/c256/arfcompics/009.jpg http://i29.photobucket.com/albums/c256/arfcompics/010.jpg Note the gash from the cam pin: http://i29.photobucket.com/albums/c256/arfcompics/012.jpg Let's see if this will help: http://i29.photobucket.com/albums/c256/arfcompics/015.jpg |
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Posted: 5/15/2012 1:21:57 PM EDT
[#12]
Also, NIB unfired BR-308 MOE
My bolt looks ok 
Impact as well 
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Posted: 5/15/2012 1:30:35 PM EDT
[#13]
Ya looks good for now. My little experiment found that if I had a bolt with the OEM cam pin, not only did it bang up against the cam pin relief area But also put significant wear on the bolt lugs. Change it out with the POF roller cam pin and excess wear stopped, I'm now sporting a new DPMS bolt with no odd wear on the bolt lugs or cam pin relief area. FYI Quoted:
Also, NIB unfired BR-308 MOE My bolt looks ok http://i610.photobucket.com/albums/tt187/3000FPS/newBolt.jpg Impact as well http://i610.photobucket.com/albums/tt187/3000FPS/impact.jpg |
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Posted: 5/15/2012 1:34:12 PM EDT
[#14]
Quoted:
Ya looks good for now. My little experiment found that if I had a bolt with the OEM cam pin, not only did it bang up against the cam pin relief area But also put significant wear on the bolt lugs. Change it out with the POF roller cam pin and excess wear stopped, I'm now sporting a new DPMS bolt with no odd wear on the bolt lugs or cam pin relief area. FYI Quoted:
Also, NIB unfired BR-308 MOE My bolt looks ok http://i610.photobucket.com/albums/tt187/3000FPS/newBolt.jpg Impact as well http://i610.photobucket.com/albums/tt187/3000FPS/impact.jpg Good to know; wonder if a few passes with a file and some cold blue on the OEM pin would accomplish anything. that looks like what gunny is doing; looks like he took a bench grinder to his 
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Posted: 5/15/2012 7:32:09 PM EDT
[#15]
Quoted:
WOW! This is NIB? Have you tried to load a round in the chamber, if you have how dificult is it to manually eject? Quoted:
Probably beaten to death already, but.... New and unfired. While I have never chambered a round in it yet, retracting the charging handle is a bit more difficult than with any AR15/M16 I've ever handled. A considerable amount of finish has been scraped off the (BCM Gunfighter) charging handle; just from simply cycling the action several times. FWIW–– the cam pin was dehorned with a dremel tool. FWIWx2–– I intend to obtain a much heavier buffer prior to the first trip to the range, as per Magpul recommendations (I installed a UBR). |
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