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  #31  
Old 01-13-2012, 09:33 PM
DaveHH DaveHH is online now
 
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Default flinglead:

Considering that the acceptance tests for the carbine manufacturers required a complete 6,000 round test (which all of them completed) with several examples of their product, it hardly seems likely that a bolt is scheduled to fail in 3000 rounds. Some of the 6K carbines were just looked at and released for issue as is, so your information is incorrect.
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  #32  
Old 01-13-2012, 09:57 PM
136th TFS 136th TFS is offline
 
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Quote:
Originally Posted by DaveHH View Post
Considering that the acceptance tests for the carbine manufacturers required a complete 6,000 round test (which all of them completed) with several examples of their product, it hardly seems likely that a bolt is scheduled to fail in 3000 rounds. Some of the 6K carbines were just looked at and released for issue as is, so your information is incorrect.
DaveHH is 100% correct. If you look in WAR BABY, you will see many test reports on carbine functioning. These are apparently word for word from US Government records.
6,000 rds. and more should be no problem for a bolt. I'd like to see where it's written that a bolt will fail in 3,000 rds.
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  #33  
Old 01-13-2012, 10:00 PM
leadman leadman is offline
 
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The primer on the fired case when the bolt broke is probably not higher pressure, but an excess headspace condition created by the breakage. The first thing to move back when the cartridge is fired is the primer,then the case. If the primer is back far enough it will flatten to various degrees.

That would be a tough spot to weld. Then you would have to have it checked for proper hardness. More cost than it is worth probably.

Glad nobody was hurt.
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  #34  
Old 01-14-2012, 12:03 PM
BQ97 BQ97 is offline
 
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Quote:
Originally Posted by flinglead View Post
No carbine Expert here but:
Have any of you read that the carbine bolt was estimated to have a 3,000 round service life? If that is true this can be expected in any carbine at some point.

I am certain I have read that this is the case, but at the moment I cannot recall the source.
Anyone?
That's not true. If it were none of the selected carbines would have passed the 6,000 round endurance test.
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  #35  
Old 01-15-2012, 11:08 PM
motorcop motorcop is offline
 
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Little touchy on the bolt life subject aren't we gentlemen? I believe, unless the punctuation is wrong, that flinglead asked a QUESTION about 3,000 rds being end of life cycle for a bolt. He didn't state that 3,000 rds was the limit. Interestingly enough when one considers there was a known bulge in the barrel this alone should have required due care in having this carbine examined by a qualified individual. Just a time bomb waiting to go off.'

Rick
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  #36  
Old 01-16-2012, 01:22 PM
Cobra Cobra is offline
 
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Location: Central IL
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I am the original poster, and you make a good point there, Motorcop. Nobody likes to have their mistakes pointed out, but in the interest of all who may be reading this thread, I did not examine that receiver rail closely enough, when the bulged muzzle should have been a red flag to give it more than a cursory inspection. And I'm a very cautious person by nature.

It's impossible to know now if the damage was there prior to the bolt failure, or if the bolt simply failed at the end of its service life, and caused the damage. Moot point really, because for me the lesson is that I should have been more diligent in looking beyond the obvious.

I am VERY thankful no one was injured. I also appreciate all the great input forum members have contributed to this post.

~ Cobra
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  #37  
Old 01-16-2012, 08:22 PM
motorcop motorcop is offline
 
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Hi Cobra: I did not mean to be pointed, but with your event and the circumstances surrounding it I think it would have been best to do what I suggested. I was digging thru some videos, You Tube I think and I saw a nasty one of a male and female firing Garands. They each had a rifle and were taking turns clicking off rounds. The female had some sort of problem and it "looks" like she puts a round into the chamber and rides the bolt almost all the way home. She fires the rifle and the things blows into pieces. Perhaps it fired out of battery, but I don't know. Interestingly viewers comment on what they think happened, but they honestly don't have a clue....they were not there! I wasn't there either but I only state what I think happened to tell the story. Anyway, I also wasn't there when your situation took place and without a lot more information I would never want to guess as to what happened. With firearms there are just way, way too many varibles. Excuse my honesty in the first post. I am glad you didn't get hurt.

Rick H.
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  #38  
Old 01-16-2012, 08:48 PM
BQ97 BQ97 is offline
 
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Quote:
Originally Posted by DaveHH View Post
Considering that the acceptance tests for the carbine manufacturers required a complete 6,000 round test (which all of them completed) with several examples of their product, it hardly seems likely that a bolt is scheduled to fail in 3000 rounds. Some of the 6K carbines were just looked at and released for issue as is, so your information is incorrect.
The 6000 round endurance test was an ongoing requirement for every shipment of carbines throughout production.
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  #39  
Old 04-10-2016, 12:38 PM
.Steve. .Steve. is offline
 
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I think a few things.

1). The loaded cartridge in the chamber under the extractor hook acts like an axle to align the bolt when forward far enough to rotate the bolt into full lockup/ battery. Otherwise, the bolt is loosely guided.

1a). Take out your favorite carbine. Allow the slide to over run the right bolt lug cam extension and go into full battery. With or without a cartridge case/loaded round in the chamber (do not shoot your house, etc.), you will probably see the left lug touches next to nothing when the right lug is all the way rearward against the receiver locking surface.

1b). This is because your carbine functions more like a Krag rotating flap bolt than it does a two or multi lug rotating bolt, say AR/AK style.

2). This thread is one of the many chicken and the egg problems. On two levels.

2a). Did the bolt break of its own accord, or did the stress of firing while only partially rotated cause it to break? Usually called an out of battery firing, but way more often partial battery.

2b). Did the damage in the left receiver lug surface or track cause stress or incomplete rotation, or did the damage occur when the right lug broke off?

3). In post 12, there is a smeared left receiver locking surface below the area a fully rotated left bolt lug would have contacted it. In post 19, there is a left receiver locking surface broken out below the area a fully rotated left bolt lug would have contacted it.

3a). Seeing a pattern? The thrust is to the rear and the bolt cannot drop because an undamaged cartridge case is still holding it upward.

3b). The only way for the top of the left bolt lug to only contact the bottom of the left receiver locking surface is if the bolt is short of full rotation into battery.

3c). Ditto, if the broken right lug now allows the left lug to come to the rear AND the left lug misses the upper half of the left receiver locking surface.

4). My SWAG is two fold.

4a). The broken bolts are often caused by out of battery partial bolt rotation firings that cause uneven and unsupported stress on the right lug.

4b). The reason there are less catastrophic failures than we would guess is that as the right lug steel material is breaking, tearing sequentially, the peak pressure decreases fast enough it all just sits there. Possibly retarded by the now engaged left lug as the right fails. This courtesy of a small pistol class medium intensity cartridge fired in a small rifle action.

4c). My guess is that the really exciting failures are a right lug previously cracked giving way faster during a second event than the pressure drops.

5). Take aways:

5a). The longer the case or the shorter the chamber, the more likely it is full bolt rotation will fail to occur.

5b). The sooner in rotation a particular carbine can fire short of full battery, the more likely the unsupported bolt will crack or break. The carbines usually fire long before full bolt rotation. There is a simple test in the sticky up top. Done with primed brass, NOT live ammo.

5c). Make sure any reload is trimmed every loading after full length resizing and neck expanding.

5d). You better be wearing impact resistent shooting glasses and ear muffs!

Last edited by .Steve.; 04-10-2016 at 12:48 PM.
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