Bullet test follow up parts break down and sight circle photo

[jond41403]

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

[INLAND44]

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.

[rcathey]

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

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.

[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.

[gunsdora]

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.

[USGI]

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

[tenOC]

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.

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.

[DaveHH]

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.