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Requesting Assistance to Identify Correct Bolt

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New2brass View Drop Down
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Dan Pinto, Photo Editor

Joined: Nov 29 2015
Location: CT
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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Apr 13 2020 at 8:23pm
The barrel "Skirt' was called the"Spacer" by ordnance according to TB 9-1276-1. The spacer is is just that. it positions the barrel in relation to the ramp.

There were misconceptions in the field when some noticed the gap between the ramp and the barrel., hence the TB.

In early barrels the skirt was extended around approximately 2/3s of the chamber end. If you look the are at 9 to 12 position is thicker.

According to WB pg 285 the changeover to the short came as a result of the long skirts being bent in transit. These barrels were salvaged by having the bent part of the skirt milled off. When no ill effects were found with this procedure it was realized the long skirt was not necessary. 

As to the scrape and dent. I have seen many receivers with the long scrape or missing finish due to the small lug riding it without propper lube.

If you look at the mechanics of the bolt on the animations here 

you will see the large lug will cam the bolt down, lifting the small lug. 

I can only think of two situations where that small lug would ride too far.
1. A cracked or partial broken large lug. There would have to be enough material left for the slide to move the bolt forward without rotating the bolt. If you look at the long scratch it ends at the peening in question.

2. Is it possible the carbine was assembled incorrectly and the bolt was not in the slide? If someone kept racking the slide it would hammer the bolt forward and possibly create that damage. I would think the forward section of the slide outside of the cam area, where it meets the arm,  would have some markings from said action. It is a longshot, but I have seen people do some strange things when a firearm malfunctions. 

I am sure there are other possibilities. 

If you look at both examples consider the shape and angle of the punch, if used. Someone would have had to grind or shape the end to create that pattern. 

Just my .02
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floydthecat View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Apr 14 2020 at 5:59am
It seems very odd that we find at least two receivers (so far) with practically the same (seemingly) tool-mark in the exact same place. Different manufacturers built in different facilities. It also seems improbable that the identical damage could occur from a random bolt failure. It just looks like a purposeful action performed for some reason. 

In any event, the “punch-mark” in question has no affect on the performance of the carbine as far as I can tell. Mine was shooting just fine before I replaced the barrel and afterwards with multiple bolts....and still is. I do not think it will be an issue in OP’s example either. As long as it doesn’t interfere with bolt-travel, shouldn’t cause a problem. Maybe just something we will all wonder about.

I will say the barrel in my action was not super tight, but I think that is not so uncommon either. The replacement barrel timed properly, but I decided to use a 15-degree shim to tighten things up. I don’t guess that I could rule out the possibility that someone attempted to tighten-up the barrel fitment during a previous barrel change, but the mark in my receiver is not as prominent as the mark in OP’s example. It certainly would not have accomplished much.
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