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Head Space Brain Work

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03manV View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 03manV Quote  Post ReplyReply Direct Link To This Post Posted: Jun 04 2020 at 10:36pm
Floyd,
we are in total agreement.Geek
Military and commercial entities and their gauges are frequently different.
I'm sure the "specified" numbers and limits are conservative- the statement
that you made when you started this thread! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sling00 Quote  Post ReplyReply Direct Link To This Post Posted: Jun 05 2020 at 6:39am
Originally posted by 03manV 03manV wrote:

Military and commercial entities and their gauges are frequently different.

Prime example is .303 British Enfield. A SAAMI specs field gauge is .070 whereas the British mil spec field gauge is .074. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Jun 05 2020 at 8:02am
I think it's a safe bet to assume there are many carbines out there shooting past 1.302, well past that. All the field gauge indicates is that head-space is longer than the gauge, it doesn't indicate how long it is and how long it's been shooting that way....unless it is accurately measured. I've looked at guns for owners in which a field gauge would practically rattle in the chamber and I am pretty sure they just keep shooting them. Like an ME gauge...it's a good indication of use, but doesn't necessarily condemn the carbine. These carbines were made to shoot rather lose with torso-shot accuracy to overcome action-pollution of mud, sand, salt-water, blood and guts. Ruptured cases due to sloppy head-space in a carbine have to be rare, if at all existent. Of course, one can blow-up any gun if he tries hard enough I suppose. These things were proofed at 140%.

A tight muzzle and a 1.295 head-space might indicate a little fired gun, but I would gladly discount the right used carbine with an ME of 3 and head-space of 1.304 by $500-$600 and take it off your hands any day. Not for a range gun that is often fired, but for one to occasionally shoot, or that "closet gun".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sawbones Quote  Post ReplyReply Direct Link To This Post Posted: Apr 12 2022 at 5:53pm
Very interesting and informative thread.  After careful scrutiny of all the opinions and facts presented I agree 100% w/ everything FloydtheCat has stated, particularly his last reply.

Toss any cases fired 3 times otherwise risk splitting/disintegrating brass

Ejector not locking?  First, check the springs in the bolt. (see CMP Forum: M1 Carbine section, "Fail to chamber question", page 3, last reply 3-5-22 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JRBrid Quote  Post ReplyReply Direct Link To This Post Posted: Apr 24 2022 at 5:11pm
Personal Experience with a Carbine that Was Out of Headspace

I’ve been hesitant to jump into this discussion, as I don’t feel it is my place to tell others what they can or should do with their guns, but I have decided to go ahead and share this personal experience with a carbine that was out of headspace.  Hope this helps … here is the story:

A few years ago, my best friend and I were enjoying a day at the range shooting carbines.  We had several with us, including one that he had recently purchased at a local gun show.  We were having problems with the new gun, several failures to fire.  Examination of the rounds showed light firing pin strikes, but the problem was not consistent and we were thinking that maybe the bolt needed a good  cleaning.  We continued shooting, when suddenly my buddy, yelled, dropped the new carbine, and backed away from the shooting bench.  I’ll let him tell you what happened in his own words:

 

There was a flash in front of my face and something hit me.  I dropped the gun and stepped back from the bench.  The case had separated.  The stock was split.  The magazine case was bulged and the base, along with the follower, spring and remaining rounds were blown out.  The extractor, firing pin, ejector and spring were missing from the bolt.   We found most of the pieces of the magazine, bolt and brass.  There was something embedded in my forehead about 1” above my glasses.  There was no sign of infection so I waited until the swelling went down and finally pulled a BB sized piece of casing brass out of my forehead.”

Obviously, this was a traumatic end to a day at the range – we were just thankful that it wasn’t much, much worse.  Using some thin washers and head space gauges, we estimated the gun in question was as much as 0.030” out of headspace.  After this experience, we very carefully checked the headspace on all of our carbines, and corrected any of them that showed excessive headspace with a field gage.  Fortunately, we were able to correct most of the issues we found by swapping bolts, but the one did require a new barrel. 

Bottom line, for us at least, is that life is too short and precious to take the risk of shooting a carbine that has excessive head space.   

We still have the pieces of brass and the stock.  If anyone would like pictures, just PM me.

Again, hope this helps. 

Respectively,

Jim

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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Apr 24 2022 at 5:43pm
Spec’s give you 22 (1.302-1.280). My experience has been they start becoming problematic much past 1.310, which would be 8 out of spec. I would think the gun would stop firing at all. Other things could be at work. The only rupture I have ever read about was eventually blamed on faulty ammo (thin brass).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Smokpole Quote  Post ReplyReply Direct Link To This Post Posted: Apr 24 2022 at 8:05pm
JRBrid, that sounds more like an out of battery explosion than a head space issue. Was that carbine by any chance a commercial carbine? Or more specifically a Universal? Universal took some shortcuts in their manufacture that allowed their carbines to fire out of battery and what you describe is classic out of battery firing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 03manV Quote  Post ReplyReply Direct Link To This Post Posted: Apr 24 2022 at 10:35pm
Please tell us about the ammunition.

I'm with Smokepole about an OOB firing, but a case head separation would do it too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David Milisock Quote  Post ReplyReply Direct Link To This Post Posted: Apr 25 2022 at 9:32am
I tend to lean toward an out of battery firing also.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JRBrid Quote  Post ReplyReply Direct Link To This Post Posted: Apr 25 2022 at 3:41pm
It was not a commercial carbine - actually a Winchester with mostly Winchester parts, including a nice Winchester stock that was split.  We considered OOB, but found couldn't find any evidence on the bolt lugs or receiver to support that.  This is the gun we replaced the barrel on, and have had no trouble with it since doing that - same bolt, same springs, etc.  The one thing we could prove was that the gun was badly out of headspace, on the order of .030 inches beyond a Forster field gage.  I will leave you to draw your own conclusions ....

Jim 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Apr 25 2022 at 4:01pm
Wow…30 past a 1.30 field gauge! I can’t see how that could not be noticed before it was fired. Not bashing anybody here….we just like to try and figure out what happened in cases like this.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sawbones Quote  Post ReplyReply Direct Link To This Post Posted: Apr 25 2022 at 5:50pm
Faulty ammo must be considered.  Was the ammo used reloaded stuff?  Must consider case separation due to metal fatigue.  Case reloaded too many times renders case thin and brittle.  That in conjunction with a way too long headspace and you've got the perfect ingredients for disaster. 

I refer all to Lyman Reloading Handbook, 49th edition , page 48. 

A new un-fired case will not disintegrate when fired unless other factors are present such as using too much powder, wrong powder, excessive crimping.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel92 Quote  Post ReplyReply Direct Link To This Post Posted: Apr 25 2022 at 10:13pm
So was the headspace on this carbine 1.36? That would swallow a field gauge right? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JRBrid Quote  Post ReplyReply Direct Link To This Post Posted: Apr 26 2022 at 12:33am
Sorry, this happened some time ago, and we no longer remember the details on the ammo being used -- not sure if it was new commercial, surplus GI or reloads.

Jim 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 03manV Quote  Post ReplyReply Direct Link To This Post Posted: Apr 26 2022 at 12:57am
I'm sorry but without knowing the ammo involved and not measuring the headspace before the accident, one just cannot draw a firm conclusion as to the cause.

The "cause" of the accident as you state was a case separation; what caused the case separation cannot be discerned from the information given.

It is good your buddy wasn't more seriously injured.

The real lesson here is to check any firearm before firing and when firing a "new, used" firearm for the first time use known "good" ammo.  When encountering an unexpected series of malfunctions it is best to stop and determine the cause.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Apr 26 2022 at 5:02am
Originally posted by Rebel92 Rebel92 wrote:

So was the headspace on this carbine 1.36? That would swallow a field gauge right? 

I don’t see how it would have fired at all under normal circumstances with the bolt closed and rotated on a chambered round. My experience is they stop shooting when it gets much past 10-12 thousandths longer than a field gauge. 30 thousandths longer than a 1.300 gauge would be 1.330.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JRBrid Quote  Post ReplyReply Direct Link To This Post Posted: Apr 28 2022 at 1:17am
We have used ammo from that same box/lot in other carbines both the day of the incident and since, and have had no other problems.  The only difference we have been able to identify is that the one carbine that we had the incident with was badly out of headspace, and all of the others gaged as good, again with all determinations being made with a Forster field headspace gage. 

Jim 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Smokpole Quote  Post ReplyReply Direct Link To This Post Posted: Apr 28 2022 at 11:38am
Was part of the case stuck in the chamber? Or was the case simply split?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JRBrid Quote  Post ReplyReply Direct Link To This Post Posted: Apr 28 2022 at 2:04pm
Yes, part of the case was stuck in the chamber.  The case completely separated just ahead of the base of the round.

Jim 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Apr 28 2022 at 2:26pm
Can we call this a case head separation as opposed to a rupture? 
The only time I have been able to find anything about a carbine case rupture was an individual who took his carbine to a gunsmith after he had one blow-up. Gunsmith determined it was a case head separation, because the owners ammo blew-up in his test gun as well…..bad ammo.


I have been present or experienced two ruptures and one case head separation in my life. All were from semi-auto 9mm pistols with unsupported chambers. The separation left most of the brass in the chamber. 
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