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 A Sane Head Space Discussion
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americanboy
Advanced Member


USA
260 Posts

Posted - 03/30/2017 :  2:42:06 PM  Show Profile Send americanboy a Private Message  Reply with Quote
I've read postings in other forums that practically result in food-fights over this very subject. It's almost enough to scare a newbie or novice to the degree they may be afraid to fire their carbine and find the need to rush out and purchase a set of gauges. Spending money they could use on ammunition. Here's my take on a practical method to ascertain the safety of your gun. Obviously, a newly barreled receiver requires the full-meal-deal.

Go: This means that the standard commercial round supposedly constructed to SAAMI specifications will chamber and the bolt will close, rotate and lock. It's not too difficult to perform this test. For safeties-sake, I'd advise stripping the bolt as one normally would for some gauges so the firing-pin is removed as well as the ejection components. If the bolt rotates and locks on a commercial round...the go-test is successful. Actually, if it's one you have fired this test has already passed.

NO GO: On a fresh gun, this is the "recommended" point at which the bolt should not rotate and lock. It does not mean head-space is too sloppy or dangerous...yet. It's just the middle-of-the-road (if you will) measurement for a gun that has lots of life left.

FIELD: This gauge is used to determine the absolute maximum allowable head space for a safe weapon. If the bolt rotates and locks on this gauge, it's reached the danger-point.

My point and question. Is it practical to assume that if one wanted to check head-space on his daily shooter, or a used purchase, that the use of a commercial round as a GO gage (if it's an unknown gun) and the purchase of a FIELD gauge satisfies most requirements to determine the weapons safety?

This is for my benefit so I completely understand it, but it may be helpful for those considering the purchase of a complete set of gauges that may be used once and tossed in the parts bin forever.

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jimb16
Moderator



USA
3043 Posts

Posted - 03/30/2017 :  3:31:57 PM  Show Profile Send jimb16 a Private Message  Reply with Quote
Unless you plan on replacing a barrel yourself, I wouldn't bother with anything other than a field gauge. I usually take it with me when I go to shows where I might invest in another carbine.

OGCA Lifer,NRA Life member, son of a 325th GIR Glider Rider
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bonnie
Advanced Member



USA
161 Posts

Posted - 03/30/2017 :  3:35:02 PM  Show Profile Send bonnie a Private Message  Reply with Quote
Buy a GO headspace gauge_________________________________________________________________measures 1.290 GO gauge.

Cut a piece of .005 feeler gauge to fit the rear of the GO headspace gauge. Hold in place with a smear of oil. This is the 1.295 NO-GO gauge.

Cut a piece of .012 feeler gauge to fit the rear of the GO headspace gauge. Hold in place with a smear of oil. This is the 1.302 FIELD gauge.

Works for the occasional headspace check of a "new" to you carbine.

Tight headspace is more of a danger to a shooter then a little loose headspace, hence start with a real GO Gauge.

Edited by - bonnie on 03/30/2017 3:36:47 PM
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americanboy
Advanced Member



USA
260 Posts

Posted - 03/30/2017 :  5:04:47 PM  Show Profile Send americanboy a Private Message  Reply with Quote
Good stuff! There seems to be variations in actual dimensions between the two most popular brands of gauges and people will simply swear by one-or-the other. I never thought that it was necessary to put on a lab coat and get too scientific.
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shadycon
Veteran Member



USA
1356 Posts

Posted - 03/31/2017 :  07:04:39 AM  Show Profile Send shadycon a Private Message  Reply with Quote
You could take an empty case that is correct length without a primer and load a bullet to correct length and you have a GO gauge.

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americanboy
Advanced Member



USA
260 Posts

Posted - 03/31/2017 :  08:16:49 AM  Show Profile Send americanboy a Private Message  Reply with Quote
Exactly! I have dummy-rounds built for all the calibers I shoot.
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swampmolly
Senior Member



USA
764 Posts

Posted - 03/31/2017 :  08:18:03 AM  Show Profile Send swampmolly a Private Message  Reply with Quote
You also could make a field gauge by soldering a piece of copper over the primer of an empty casing and using a micrometer or calipers file it down to 1.302. (This can be used in any carbine without removing the extractor and ejector from the bolt.)
You take it a step further by making a duplicate field gauge and file it down until the bolt just closes and then you know exactly what your head space is, hopefully it is somewhere around 1.296. (make sure the casing extension dose not touch the extractor or ejector pin. )
SM
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americanboy
Advanced Member



USA
260 Posts

Posted - 03/31/2017 :  08:42:03 AM  Show Profile Send americanboy a Private Message  Reply with Quote
I ran across a Youtube where one guy was using scotch tape on the base of a perfectly sized dummy-round to measure his head space. Scotch tape is .001 thick. I guess that would work on a "tight" action, but one could wind-up with a sizeable gob of tape on a well-fired gun.
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RASelkirk
Greenhorn Member



41 Posts

Posted - 03/31/2017 :  5:43:43 PM  Show Profile Send RASelkirk a Private Message  Reply with Quote
quote:
Originally posted by americanboy

I ran across a Youtube where one guy was using scotch tape on the base of a perfectly sized dummy-round to measure his head space. Scotch tape is .001 thick. I guess that would work on a "tight" action, but one could wind-up with a sizeable gob of tape on a well-fired gun.



I've used multiple layers of scotch tape on the a$$ end of dummy round, just be sure to use a quality dial caliper to verify the final dimension.

Russ
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jlwilliams
Junior Member



USA
78 Posts

Posted - 04/24/2017 :  3:43:11 PM  Show Profile Send jlwilliams a Private Message  Reply with Quote
Headspace is something that people make out to be deep dark voodoo, not to be spoken of by the uninitiated. It's not that big of a deal. It's a measurable dimension on a machined device. Depending on the action you can use a sized, measured dummy round and a set of feeler gauges to figure out if you do or don't have a problem. The Carbine isn't the easiest action to check that way, but I like the oil and shim stock idea. If it closes on a case and too much shim, I'd rent a proper gauge. It's cheap and easy online these days to just get those shipped to you, use them and send them back. If it doesn't close on a case and some shims, you don't likely have a headspace problem.

Headspace problems aren't as common as erosion problems. If you shoot old guns, chamber casting and bore slugging are more likely to identify issues than stocking up on a bunch of gauges.
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americanboy
Advanced Member



USA
260 Posts

Posted - 04/25/2017 :  10:02:29 AM  Show Profile Send americanboy a Private Message  Reply with Quote
Spare bolts were issued to the troops who carried the carbine. Due to it's relative tender nature, having the extractor and ejector components confined within the bolt....could this be the main reason for carrying a spare, or is it an issue with a carbine going-out of head-space tolerance more-so than say the Garand or M14 which basically employs the same bolt design? Is it the fact that you could correct extraction and ejection component issues with a simple bolt-change? Is the carbine more susceptible to these issues than any other battle-rifle of the same era?

Edited by - americanboy on 04/25/2017 10:03:31 AM
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jimb16
Moderator



USA
3043 Posts

Posted - 04/26/2017 :  7:05:26 PM  Show Profile Send jimb16 a Private Message  Reply with Quote
Head space was generally NOT a problem with the carbine. Spare bolts were available for quick replacement due to extractor issues. You don't even need to disassemble a carbine to install a new bolt. The job can be done in the field in around 30 seconds, if you know how. It is a super fast way to get a disabled carbine back in action FAST!

OGCA Lifer,NRA Life member, son of a 325th GIR Glider Rider
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myname
Advanced Member



USA
209 Posts

Posted - 04/28/2017 :  05:57:10 AM  Show Profile Send myname a Private Message  Reply with Quote
jimb16, I can remove and reinsert my flat bolt without disassembling the Carbine, but not with my round bolt in it. Am I not doing it right, or should I only be able to do so with the flat bolt? And just to stay on thread topic, I made my dummy bullet 1.290 Go Gauge and own a No Go gauge. If I didn't own the No Go gauge I'd buy a Field Gauge in it's place.
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americanboy
Advanced Member



USA
260 Posts

Posted - 04/28/2017 :  06:23:29 AM  Show Profile Send americanboy a Private Message  Reply with Quote
There is a you tube video out there of a guy removing the bolt in this fashion. He is demonstrating the procedure on a round bolt. Just Google "how to remove a carbine bolt".

Edited by - americanboy on 04/28/2017 06:24:25 AM
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Filroy77
Starting Member



USA
16 Posts

Posted - 07/16/2017 :  6:14:58 PM  Show Profile Send Filroy77 a Private Message  Reply with Quote
I don't have dies for the .30 carbine yet as I'm trying to get a national ord inc going before investing. Could I pull a bullet and use an empty case for the headspace gauge?

This rifle has multiple issues, light/no strike, weak ejection when it does fire. Won't strip a round out of the magazine. I'm taking one step at a time. Replaced all the springs in the bolt and trigger group that seemingly did nothing to the performance. After spring replacement, I shot it and the rounds that did fire, had the spent primer pushed half way out of the spent case. Wondering if headspace is the issue there?

I'll look into the gas system next when I educate myself how to get it apart.

The mags came with weapon that my uncle gave to my dad many years ago (25-30?) I bought some new springs for those as well but neither functioned.

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americanboy
Advanced Member



USA
260 Posts

Posted - 07/16/2017 :  6:47:13 PM  Show Profile Send americanboy a Private Message  Reply with Quote
Looks like you have several issues in front of you Filroy...lets not let head-space measurement be one of them. You can easily check head-space without using some of the $$$ for a set of gauges that you seem to possibly need to get this gun running. Obtain a good measurement tool, like a digital caliper. This is stuff you can't use a tape-measure or a yard-stick for. Measure the case length of a loaded round, or you can pull the bullet on a live round if you're bothered by using it. You should be using the stripped bolt anyway, so there won't be much danger of setting off a primer. Once you get an accurate measurement on the case length, chamber the round/case and make sure the bolt will rotate and lock under finger pressure. This can be subjective, but just don't "force" anything. Remove the round/case and add some form of shim-stock to the base in small increments. Scotch-tape applied in layers and trimmed with a razor-blade works, but you can use feeler-gauge material. Add the shims to the base and after adding "some" insert the round/case in the chamber and see if the bolt rotates and locks. Do this as necessary by adding shim material until the bolt will not rotate. That is the point at which you have maximum head-space. Measure the case again with the shims applied and subtract your measurement you made earlier without the shims. This number is the actual head-space and it's useful to see how lose the lock-up is. What you have done with the round and the shims is create your homemade field gauge. Field gauges are something like 1.301-1.302. That is the point at which the gun should not be fired. If it closes on a measurement of 1.301-1.302...you're in trouble. If your measurement of the case plus the shims is below this, you have life left in the gun. 1.295 is the no-go gauge measurement. If your results come in close to 1.295...that's perfect and on a fresh gun, it should be close to that. Anything between 1.295 and 1.301 is good-to-go. If for some reason, your test result in a measurement of less than 1.290, your head-space is too tight and you should not fire the gun, unless you trim cases to below that.

In summation...it should close on a 1.290. It "may close" on a 1.295. It MUST NOT close on a 1.301.

Edited by - americanboy on 07/16/2017 6:53:30 PM
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Filroy77
Starting Member



USA
16 Posts

Posted - 07/16/2017 :  7:36:00 PM  Show Profile Send Filroy77 a Private Message  Reply with Quote
Thank you Americanboy. I do have a digital caliper. I have a round with the bullet pulled but still primed. I'll disassemble the bolt and check it out.
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Tuna
Moderator



3155 Posts

Posted - 07/16/2017 :  10:06:33 PM  Show Profile Send Tuna a Private Message  Reply with Quote
In the photos the dimple on the far right case primer is not from a light hit. It is from the firing pin being pushed back as the bolt closes and the case is in the chamber. IF the barrel does have excessive head space a good machinist can take the barrel down a few thousands and enough to reinstall the barrel properly again. If a small amount extra was removed then it can be reamed out to new again. But it is highly unlikely that a barrel was fired enough to create such a problem. The military used to test carbines to 15,000 rounds and still had good head space. I would also suggest that you try a different brand of ammo. You may find it makes a big difference.

Edited by - Tuna on 07/16/2017 10:08:15 PM
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americanboy
Advanced Member



USA
260 Posts

Posted - 07/17/2017 :  05:41:31 AM  Show Profile Send americanboy a Private Message  Reply with Quote
Those backed-out primers point to a serious problem. Very short brass or very long head-space, which will cause light strikes as well. The M1 Carbine was very forgiving on head-space. It was meant to be rather lose to be able to function in the sand, water, ice, snow, rain, blood and rotten jungle conditions. Never meant to be a tack-driver, but very reliable and forgiving in horrible conditions left uncleaned for extended periods. However, it does have it's limits. The minimum case length is 1.28 and a field gauge is 1.301. This equates to some .021 of head-space before the gun is deemed unusable.

Realize that you have one of the early commercials and parts were often scrounged from piles of left-overs or rejects...especially receivers. Like other commercial manufacturers, some NO guns could have USGI components until they dried up. As time passed, cast components from various sources were used. I would make sure the receiver and barrel pass muster B4 I'd invest any money in it. Good Luck!

Edited by - americanboy on 07/17/2017 07:19:17 AM
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jimb16
Moderator



USA
3043 Posts

Posted - 07/18/2017 :  6:30:53 PM  Show Profile Send jimb16 a Private Message  Reply with Quote
Wait a minute of the headspace problem for backed out primers! Is the ammo reloads? If so, then the powder charge was too light! The light primer strikes are most likely a bolt that didn't close properly. A light powder charge in a reload would also cause failure to feed, failure to fire (doesn't cock the hammer) and ejection problems! ALL of the problems you describe could be caused by bad ammo!

OGCA Lifer,NRA Life member, son of a 325th GIR Glider Rider
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Filroy77
Starting Member



USA
16 Posts

Posted - 07/20/2017 :  8:46:55 PM  Show Profile Send Filroy77 a Private Message  Reply with Quote
Not reloads, Armscor USA. Just got some Remington UMC and a new pro mag. Still have the weapon apart so it'll be a bit before I can try them.

Non fired cases are at 1.2860 - 1.2870 in.

Edited by - Filroy77 on 07/20/2017 8:51:51 PM
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americanboy
Advanced Member



USA
260 Posts

Posted - 07/21/2017 :  08:33:42 AM  Show Profile Send americanboy a Private Message  Reply with Quote
1.28 is the minimum spec. length, but a well-worn gun may not shoot it. In the process of figuring this out, use some longer cases, but not so long that they won't chamber and lock-up. I have one commercial that no-goes at 1.291...very tight gun. I have the bolt spec. that a good friend sent me and I can send you that. Some commercial bolts differ in critical dimensions and I have one commercial carbine that will only head-space reasonably with the commercial bolt, GI bolts are too sloppy for the gun.

Edited by - americanboy on 07/21/2017 08:35:05 AM
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Filroy77
Starting Member



USA
16 Posts

Posted - 07/21/2017 :  7:15:51 PM  Show Profile Send Filroy77 a Private Message  Reply with Quote
Got around to bolt disassembly and checking the head space per instructions above. Started with an unfired case, no bullet, no powder, still primed measuring 1.2870. Kept adding tape to the end till the bolt wouldn't close. Peeled back one layer of tape and it would just close. Measurement was 1.3105. A difference of .028.

I'm deeply saddened by this. Any affordable fix? Would a new bolt make any difference? The Remington cartridges are at 1.2860 or so. Untrimmed brass would be unsafe?
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jimb16
Moderator



USA
3043 Posts

Posted - 07/21/2017 :  7:17:06 PM  Show Profile Send jimb16 a Private Message  Reply with Quote
Armscor ammo is NOT the best stuff in the world. In fact, I won't even save the brass for reloading. It wouldn't surprise me one bit if you find that the problem was the ammo and nothing else! I wouldn't take that junk if you tried to give it to me.

OGCA Lifer,NRA Life member, son of a 325th GIR Glider Rider
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Filroy77
Starting Member



USA
16 Posts

Posted - 07/21/2017 :  10:27:16 PM  Show Profile Send Filroy77 a Private Message  Reply with Quote
I will try the new Remington ammo and pro mag.

The bolt appears to be well worn at the inside stop.

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americanboy
Advanced Member



USA
260 Posts

Posted - 07/22/2017 :  06:08:49 AM  Show Profile Send americanboy a Private Message  Reply with Quote
It won't matter what the case length is for the test. Since you have added shims to it and arrived at an overall head-space of 1.3105....that's way out of the 1.301-1.302 field gauge spec. If you could produce a case longer than 1.29, it may move the base closer to the firing pin to get it to fire, but you're exposing much more unsupported case out the back of the chamber inviting a case rupture. I've seen case ruptures and it's not a pretty sight. Even though the lug looks severely damaged, you are pushing the bolt with your fingers to test the head-space "past" that lug damage. The bolt obviously needs replacement, but as far as your test goes, I don't think the lug damage is relative.

To determine if a bolt change will help, you need to measure that bolt and see if/how far out of spec it is. If you will PM me I can send you the spec. You can make a couple of basic measurements. If the bolt is okay, a replacement bolt is not going to do you any good. The gun will need to have the barrel removed and adjusted, as well as a new bolt just due to the lug damage on that one. You may be out-out-the-money here, unless it's a family treasure. You may have a wall-hanger. PM me with an e-mail address and I'll send you the bolt spec.

Edited by - americanboy on 07/22/2017 06:35:23 AM
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