Bullet test follow up parts break down and sight circle photo

Hey guys,
I did buy the carbine from the Bullet test post. The barrel is marked Saginaw SG General Motors no date stamp (Import marked). The receiver is a Saginaw #3257045. Magazine is marked K.I. Magazine release marked with an M. Trigger housing, hammer and bolt are Inland. Rear sight appears to be post war replacement SA with a shield with what looks like an M in it. Stock has been refinished but looks like a Saginaw with a faint RSG in the inside of the fore end. Handguard not market.

I have added a picture of the circle on the front sight. I think it is a machine mark, no numbers or letters inside the circle.


If anyone has a round bolt (complete) for sale at a reasonable price let me know.

Looks like the start or finish of the machine cycle... A WTB in that forum should find what you seek.

Another bolt will require fitting by a smithy. Bolts are not drop in parts.
Not all Saginaw barrels were dated. Saginaw, Grand Rapids didn't make barrels at all. That'd be the S'G' or IP(Irwin-Pedersen who lost the contract). stamp Saginaw.
There were 3 types of front sight. Milled, not all of which were marked, stamped and cast. Best to go here and rummage around the 'Parts' page. The 'M' might be a 'W' for Winchester. Just a guess though. Sights used by most makers had an 'N'. Might be an imporeter's mark too.
Remember, Carbines are fun. Even when they make our heads explode.
The U.S. Caliber .30 Carbines

I'm not doubting you, I too have heard that if you change any bolt in any firearm that you must have the headspace checked, but wasn't the whole reason for the M1 carbine to be so successful was because all of the parts were interchangeable safely no matter who the manufacturer ? Safely dropped in parts was the entire idea wasn't it?

My 2 cents worth. Originally acquired a Underwood barrel/ receiver/ bolt/ trigger group (barrel date 2-44) and scrounged parts until I had a functioning M1. The bolt that was with it was a round "A.I." marked. Later a friend gave me a complete "SG" flat bolt and I thought it looked better than the round, so I swapped them out. I manually cycled rounds through it fine & it locked up tight. First time I took it to shoot, I fired a few rounds through it holding it at arm's length, just in case.

No problems/ no gunsmith. I tend to agree with "jond41403" that parts were made to be "field expedient" in time of war.

I mean no disrespect at all towards sunray because his advice is 100% correct for 99.9% of all firearms that have bolts.the m1 carbine I would consider the exception because if I am not mistaken, the M1 carbine was the first of its kind to be designed with such strict manufacturing specifications, all parts including bolts we're supposed to be able to be swapped out without any worry of safety issues.it's one of those instances that seems to go against everything we were taught about firearms safety, but in the case of the carbine, it is supposed to be perfectly safe to do so. It's kind of like we are always taught to never put our fingers inside the trigger guard until you are ready to pull the trigger, but on an M1 Garand you have to put your finger in the trigger guard just to disengage the safety. I would do like boonie stomper did, after dropping in the new bolt, hold it out at arm's length at first until you get comfortable and confident with the new bolt

Head space checking should always be done. For Safety.

The only Carbines I remember not head spacing were (1) an early Winchester I rebarreled (2) a Winchester I bought with an odd barrel and an IP I rebarreled. None were a result of swapping bolts.

Can't remember ever having a Carbine that wouldn't head space due to bolt swap.

While carbine headspace is overhyped, those who are unwilling or incapable of understanding the physical relationships should be cautious - just as those who know nothing about electricity should probably get someone else to install their ceiling fan. Those lacking a basic understanding should always avoid taking advice from those who know less than they do. (unless, of course, you hear 'some guy' at a gun show say all is well, then you're good to go:madsmile:)

Since the carbine headspaces on the case mouth, if lacking headspace gauges, a 'better than nothing' check is to add shims to a fired round until the bolt won't close by hand - then mic this assembly. A Coke can is very close to .003" Chinese crap digital calipers are available at Harbor Freight for about $10.

For those who claim there cannot be an issue, perhaps they can answer these questions:

1. If every bolt worked in every carbine, then why did the Army acquire headspace gauges?
2. Has no one ever replaced a barrel after the carbine left the factory? How would you verify the new assembly was in spec - except by checking headspace?

For those on the other side:

1. Do currently available headspace gauges come with a calibration certificate ? (If not, then you're basically ****ing up a rope when concluding anything.)
2. Do you measure every round's case length before firing to make sure that it too is within spec?

Finally, who said this: Excessive headspace, due to wear, may be caused by worn faces of bolt, worn locking lugs on bolt, or worn locking shoulders in the receiver.

For those who lack an understanding of the basic concepts, here's a question to explore: what is likely to present more danger, inadequate headspace or excessive headspace.

Let's see, I have a 75 year-old M1 Carbine that probably was given to some foreign country at some point and re-imported, with no possible way of knowing who has done what to it except it obviously has had many parts swapped out, and I'm going to just drop a different bolt in it and shoot it. Okay, but tie it to a tree and tie a string on the trigger to shoot it. :)

Guys, I have had several carbines with long or short headspace. They have to be checked before firing with gauges. Arms length does not cut it. I can't believe grown men would say such a thing.

What's funny is I asked the bolt changeability question not even a month and a half ago in a thread titled"need help identifying the stock on my carbine"in this very forum. I asked if I had to be concerned with the headspace if I were to change an Underwood round bolt marked .u. with another New Old Stock still in the wrap Underwood round bolt marked the same. I was told that it would be fine to do so, just like I have read on many other forums that it is okay to do so safely. No rebuttal at all from any other forum members whatsoever. Now that I (a new forum member) pass along the exact same information, the beginnings of a forum thread meltdown.i guess it boils down to who is giving the advice, a new member or a long time member of what kind of reaction will come forth. And as for the forum member that warned the OP of taking advice from someone who knows less then the Op, I'm not really sure how he knows what I do or don't know, but we will stick with that because it sounds nice

Well regardless of what may have been posted before it is standard procedure and critically important to gauge a rifle when changing the bolt. Have thousands of guys done it without gauging and got by with it? Yes, but its such a minor process there is no excuse for skipping it, even if you have to pay to have it done - that's what I do because its so seldom that I would change a bolt. I really don't shoot that many rounds and I have a number of rifles, so I never wear anything out or break anything.
Although, just yesterday I had to put a new spring in an AR. When I made it, I used a refurbished M16A1 stock, tube, spring and buffer. I assumed the spring was new/good but that was a mistake - I should have put a new one in. So I was shooting some fairly hot IMI 77gr last week and popped a primer so that's when I started looking for anything in the gun that may have abetted that process. When I tried the new standard recoil spring and saw how much stiffer it was than the old one, I knew I had found at least part of the problem. The other part is this ammo is known to blow primers particularly when the set-up is iffy, like mine was.

Quote:

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Originally Posted by INLAND44

...its such a minor process there is no excuse for skipping it....

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I think that about sums it all up right there.
I've been buying a few semi auto handguns lately. Wolff spring kits are about $15. Necessary? Maybe not. Minor process/investment for a bit of peace of mind? You betchya.

If you fire a carbine and then look at the fired case finding the primer is backed out even a small bit then you have a headspace problem. Can be corrected easily but it should be address before continuing to shoot it as it will only get worse with shooting.

If you play with a M1 carbine today & you change bolts or barrel it is best to buy a field gauge & check the head space. And if you reload your brass should be trimmed before a reload. Don't forget it is your face behind that rear sight you want to keep everything were it belongs.

I bought a Saginaw a few years ago I would guess a rebuild . Took it apart cleaned it then check the head space. Was very surprised when the bolt closed on the Field gauge . I changed bolts it also closed on the field gauge. I did that on 5 bolts & they all closed on the field gauge. I have had over 140 carbines off & on since 92 Most were good for head space on the NOGO gauge a few closed on the NOGO but were good on the Field gauge.. It only takes one bad carbine to loose your face & a bad bolt will do that. Buy a field gauge & be safe.

I think my Field gauge is 1.302 - not all manufacturer's gauges are the same. I've got an Inland that will close part way on the Field gauge. I'm not as afraid of that one as I am a recently purchased Underwood that would only partially close on a 1.290 GO gauge. I swapped in another bolt that lets it close on the GO gauge with about .001" clearance behind the bolt lug. So, I'm a believer in having all three gauges, just to make sure. - Bob

Quote:

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Originally Posted by Bruce McAskill

If you fire a carbine and then look at the fired case finding the primer is backed out even a small bit then you have a headspace problem. Can be corrected easily but it should be address before continuing to shoot it as it will only get worse with shooting.

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I bought one locally, the owner shot it in my presence (in front of his trailer shooting across the road into a pond that wasn't comfortably far enough away from his neighbor's house) and when I picked up the cases some had side punctures. Turned out they were his reloads.

If headspace isn't important, why did they check it during the 6,000 round tests? For different reasons(cases too long) the carbine is an exploding gun. Not many US military guns can say that, but the carbines were fond of firing when out of battery which blew the bolt, maybe side rails and for sure the stock. This was a product of too little headspace.

You can buy headspace gauges that work without disassembling the bolt. They are less than $20 and you really only need one, the field. Carbines are like 45 ACP, they can fire and do fire with the extractor holding the case against the bolt face. Because it does this doesn't make it right. No offense, but I wouldn't want to hang around with people who would hold a carbine at arms length, grimace, turning the head and after firing several rounds consider case closed. Safety check complete. What if it blows on the next shot and you or someone else loses an eye? US military arms have been parts interchangable for 150 years. It means nothing until you measure what's going on . They didn't mark parts so you would be assured that they would fit, they marked them so they would find out who made parts that Did Not fit.
I would suggest buy a field gauge, use it correctly and you will remove all doubt. When you get ready to sell it it could be a deal killer if there is excessive HS. Headspace is one of those things that doesn't matter a whit until the gun blows up then it really matters.