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Bolt Replacement

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Vic Anderson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Vic Anderson Quote  Post ReplyReply Direct Link To This Post Topic: Bolt Replacement
    Posted: Dec 02 2019 at 5:43pm
I have a 30 cal carbine with a cracked bolt. The original flat bolt was marked with a W. I ordered a replacement flat bolt, thinking that it would be an easy replacement. The replacement flat bolt is marked with "AI". When we put the replacement bolt in it jams because the locking flange on the bolt is slightly different, the original is more tapered on the edges and isn't as squared off.
Do I need to find a flat bolt marked "W" so it will fit?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 02 2019 at 6:43pm
Bolts are suppose to “play” backwards and forwards in any USGI carbine, but I have found that not to be the case 100% of the time. One should always check head-space, even if it seems to fit and function perfectly. That aside, I think you are referring to the front of the right bolt lug. Some were pointed and some rather blunt or rounded, but they are all suppose to work. Issues may come into play, such as the slide type and wear and the barrel skirt in the chamber. Round bolts are deemed to be the better bolt with either lug profile and may ride the receiver channel  bit tighter. It should not matter which prime contractor made the bolt. The AI is inland, which should not matter.

I have one carbine that simply does not like a flat bolt or a round bolt with a blunted right lug. So, there can be peculiarities that occur due to wear on several components.

I guess I have not been a great help in solving your problem...maybe try to find someone local that will let you swap bolts around to try and determine the cause. Could be the bolt, slide or a rub in the chamber on the barrel skirt, but manufacturer should not matter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: Dec 02 2019 at 6:53pm
Agree with all that floydthecat said, and I am assuming that your carbine is a USGI carbine. Make sure your receiver is cleaned and lubed where the bolt lugs ride, chamber clean? Open the below link for more info about bolts.
http://www.uscarbinecal30.com/bolts.html

Edited by W5USMC - Dec 02 2019 at 8:11pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Dec 02 2019 at 7:06pm
let's back up a bit. You say that your Winchester bolt broke a lug. Did you carefully inspect the receiver lug matting areas for bot lugs? Check for burrs or deformities.  Look for cracks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 02 2019 at 7:41pm
Originally posted by New2brass New2brass wrote:

let's back up a bit. You say that your Winchester bolt broke a lug. Did you carefully inspect the receiver lug matting areas for bot lugs? Check for burrs or deformities.  Look for cracks.

Absolutely! There is some reason the bolt cracked and the reason the replacement won’t fit....could be the problem still persist. Maybe the replacement bolt is telling you something. 

Like Dan mentioned, a burr anywhere on any contact surface, or maybe head-space. Maybe this carbine needs to see the doctor?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 8:08am
The Carbine I bought with a broken bolt had been used in full auto we assume. The guy who I got it from said the disconnect lever was still in it when he got it. Anyway, the left receiver slot had a good sized burr which interfered with the replacement bolt. The burr was caused by the bolt breaking, I'm sure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 12:07pm
I can offer a real-life experience as opposed to just reading about someone else's problem. I have broken a bolt. It cracked where all of them I've seen do...across the right lug. I never could find any damage in/to the receiver, or any mechanical reason why it broke, but I can offer a couple of suggestions.

It was an N 14 and if one does the research, he will discover cracking was/is a common problem with the N 14 flat bolt. Also, with that bolt in that carbine head-space was long...very long. So...maybe I can chalk it off to an N 14 or maybe long head-space. I do know that I simply slipped in a round bolt that head-spaced and it's been shooting ever since.

Maybe take this away from my experience. If one cannot find any burrs, rubs or obstacles impeding bolt-travel, be double doggone sure you check (or have it checked) the head-space.

When I made my first post, I was a victim of what is often human nature, but we always say never do it. I assumed everything on/in the gun was okay...just a broken bolt. Anytime one breaks a bolt, they need to try and determine why. Maybe it was just a broken bolt, but everything in the action needs to be inspected/corrected before it's fired again. The next time may just cost the shooter and eye, or some new glasses if he's lucky.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 12:55pm
Here's a Saginaw SG.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 1:18pm
Something jumps-out at me on that bolt and I have seen it b4. If you look at that bolt face-on, notice the wear pattern across the top from the 12 to 3 o:clock position. I think there is only one place that could cause that wear. The transition from thick-to-thin section on a long barrel skirt. That just about has to be a rub from the barrel skirt and I have seen it before so severe that it will impede the unlocking bolt rotation. Bolts at or on the low end of tolerance will work while bolts on the fat end of tolerance will hang. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 1:54pm
Not sure I'm seeing that.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 3:21pm
The bright wear-mark on the top of the front skirt...not the nose itself. Bolts I have seen and used do have that wear, but if it is severe enough, it can create a bind against the lower edge of the skirt. Seems to me it’s the only point that would cause that wear. As the bolt locks and unlocks, that area can/will make contact with a barrel skirt. I have one that does and opposed to polishing the skirt at that point, I just use a bolt that does not rub. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Vic Anderson Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 4:33pm


I have finally been able to upload pictures of my bolt. The crack can clearly be seen in my original bolt and the darker bolt is the replacement. The problem is the shape of the flange (lack of a better name). The original is not as large or squared off as the replacement bolt. This is causing the bolt not to travel smoothly, and has the potential to jam.

Why is the original bolt different. Original bolt is marked "W", the replacement bolt is marked "AI"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 4:52pm
Slight changes were made to the bolt design as manufacturing progressed. Regardless of what manufacturer made the bolt (within the prime contractor family) any of the bolt variations should fit and function in any USGI carbine. I had mentioned a “but” before and that “but” is there are cases where they won’t for various reasons. I understand that GI’s entered combat with a spare bolt head-spaced to their personal carbine to insure they had a safe spare.

As mentioned, there may be a condition in the gun that caused the first bolt to crack, which is interfering with the replacement.

The vast majority of the time, one can stick just about anybody’s bolt in anybody’s carbine and it will work.....but not always. I think you are going to have to find some parts to substitute and isolate the problem, or have a competent smith figure it out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 7:24pm
Vic, check out our animation page on the cycle of the weapon. There is not one that is explicitly for the bolt riding on the cam, but you will get a general idea of what is going on.


A good read would be our Bolt page withing the parts pages.


Quote: One of the great things about the .30 caliber Carbines is all parts were interchangeable regardless of who made them or when. Changes in parts designs were made to cut production costs and time, improve reliability and/or function, and/or to increase safety. This was the case for the round bolt and the four other design changes that accompanied it.

Another good read on broken bolts, slides and cracked receivers

Your W was made by Winchester, the AI was made by Monarch Marking Systems for Inland. Again all are designed to interchange with only the head space needing to be checked.

If you look at the mechanics of the different lugs it seems that it effects timing of the cam ever so slightly. The later bolts when used with the later slides did increase the dwell time to reduce muzzle flash. However, It was done so that all parts remained interchangeable.

Is your Winchester a very early carbine? The reason I ask is a very early slide or barrel may have issue, but unlikely.

Did you look at the slide cam where the bolt rides for a burr? Did you try a little oil on it?

@Floyd: can you cite where you heard soldiers were carrying extra bolts? The numbers of spares does not support that and I have never heard of wide spread bolt breakage. I would not think the carbine would be so successful nor inspiring to the troops if they had to carry an extra bolt.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 7:31pm
Originally posted by Vic Anderson Vic Anderson wrote:

Why is the original bolt different. Original bolt is marked "W", the replacement bolt is marked "AI"


Your "W" bolt is a Winchester bolt, the "AI" bolt is an Inland bolt. As for any differences, did you read the link that I provided above? It explains the design variations in bolts

http://www.uscarbinecal30.com/bolts.html
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Vic Anderson Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 8:24pm
I wish that my father was still alive, he was already a gunnery sgt when he landed on Guadalcanal in the first wave. He was on a 105 crew firing most of the night and repairing weapons during the day, he would have been able to give me a quick answer to my problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Dec 04 2019 at 5:53am
Originally posted by @Floyd: can you cite where you heard soldiers were carrying extra bolts? The numbers of spares does not support that and I have never heard of wide spread bolt breakage. I would not think the carbine would be so successful nor inspiring to the troops if they had to carry an extra bolt.<br>
[/QUOTE @Floyd: can you cite where you heard soldiers were carrying extra bolts? The numbers of spares does not support that and I have never heard of wide spread bolt breakage. I would not think the carbine would be so successful nor inspiring to the troops if they had to carry an extra bolt.
[/QUOTE wrote:



I likely could never put my finger on anything in writing, just remember some discussion from a thread some time ago and it may even have been on another forum. As I recall, a “seasoned” member mentioned it. Do I remember reading about or seeing a spare bolt pouch, but tha

I likely could never put my finger on anything in writing, just remember some discussion from a thread some time ago and it may even have been on another forum. As I recall, a “seasoned” member mentioned it. Do I remember reading about or seeing a spare bolt pouch, but that may have been for another weapon?

It’s probably something done by some particular unit or armorer and not mandated. 



Edited by floydthecat - Dec 04 2019 at 6:43am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Vic Anderson Quote  Post ReplyReply Direct Link To This Post Posted: Dec 04 2019 at 11:04am
W5USMC, After reading the article on Bolts it appears that I need to locate a replacement bolt with a "Curved Bolt Lug, the replacement bolt that I purchased has a "Pointed Bolt Lug". So the hunt is on for a replacement bolt to fit my rifle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: Dec 04 2019 at 12:04pm
Originally posted by Vic Anderson Vic Anderson wrote:

W5USMC, After reading the article on Bolts it appears that I need to locate a replacement bolt with a "Curved Bolt Lug, the replacement bolt that I purchased has a "Pointed Bolt Lug". So the hunt is on for a replacement bolt to fit my rifle.


Vic, You can try that, but as everyone has mentioned any bolt should work regardless of lug design, they are all interchangeable. I believe the better option is to try to figure out what may have caused the crack in your original bolt. As New2brass mentioned, have you checked the receiver for any deformities, burs ect.. how about the chamber. When you say that the new bolt will not lock closed, is that on an empty chamber? Can you post some pictures of your receiver where the bolt lugs ride and a picture of your chamber? Also I don't think that you ever mentioned what manufacturer made your carbine, I think that we are all assuming that it is a USGI carbine and not a commercial version, is that correct?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote painter777 Quote  Post ReplyReply Direct Link To This Post Posted: Dec 04 2019 at 2:07pm
Originally posted by Vic Anderson Vic Anderson wrote:

This is causing the bolt not to travel smoothly, and has the potential to jam.  

Quote above is with the replacement bolt in.

My concerns are.....
What is causing the replacement bolt to NOT travel smoothly and the potential to jam ??

At this point I fear the OP has been 'Information Overloaded'.
Would recommend this carbine be taken to a gunsmith for inspection.

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