.30 Carbine - Excessive Headspace?


#1

Last Friday while I was at the range, there was a pile of about 20 fired .30 Carbine cases (all LC 52) on the ground. About half showed the bulge at the base as shown, and the rest looked normal. This seems like an extreme instance of excessive headspace. However, I don’t know how that could happen, or why only about half the cases showed this condition. Further, the primers did not have the appearance of excessive chamber pressure. Any ideas? I have never seen anything like this.


#2

Boy, I have never seen anything like this before either, and I have shot the U.S. Carbine plenty.
It almost looks like the weapon is firing very much out of battery, with the cartridge not fully seated in the chamber. I don’t see how a carbine could even have that much excessive headspace with the bolt fully closed. Still, a carbine should not be able to shoot with the bolt open that far, as the cam at the back of the bolt should not allow the hammer to hit the firing pin with the bolt not, at the very least, almost completely rotated shut.

I don’t think these would fire in that position even in a carbine altered in France for the .30 Court cartridge, a shortened version of the .30 U.S. Carbine round that was intended to get around French laws about guns in current military calibers.

Weird. Keep us posted if you find out from a gunsmith what is doing this. The brass in those cases must be good not to have blown out completely with that kind of bulging! It sure doesn’t look like the cartridge bases were supported at all at the moment of firing.


#3

How about this for a wild guess: The locking lug of the Carbine has sheared off and the weapon is basically operating in straight blow back mode?


#4

Firing pin frozen forward or broken FP safety? That might allow firing to occur before the bolt had fully closed. The carbine has a tough case head, good thing in this instance. Might also be from a Marlin rifle, I remember these having some issues. JH


#5

Trying to diagnose a problem that severe is impossible without having access to all of the information. All that we have is a couple of fired cases. For all we know, that may be exactly what the chamber looks like.

BTW, excessive headspace would not result in those badly bulged cases. Insufficient headspace could.

Ray


#6

I think Ray is on the right track. This looks to me as if these 30 Carbine rounds were fired in a chamber intended for another caliber cartridge, perhaps not even a .30 caliber weapon. About 50 years ago, at a range I found some Rum-UMC 7mm Mauser cartridges with a strange double shoulder. I eventually realized that they had been fired in a 7.65 Mauser chamber. I’ve been shown 9mmP fired cases that look pretty normal after being fired from a 7.63mm Mauser pistol. NRA Museum use to have a deer rifle made from a 6.5mm Jap rifle, rechambered for 30-06 by a hunter who used for a number of years successfully hunting deer in Colorado before he took it to a gunsmith because he thought it had a bit too much recoil! This kinda looks like a rifle chambered for a rimmed cartridge of some caliber that would almost accept a 30 Carbine round. Still hard to imagine how it would fire being this much out of battery. Again, just a guess.
Cheers,
Lew


#7

Lew - are you sure the “double shoulder” cases you found were 7 x 57 mm fired in a 7.65 Mauser rifle? Despite the many dimensional differences in the two cartridges, the shoulders are in about the same place on the two rounds when measured from the head of the cartridges. However, the double shoulder is a normal characteristic of the 7.5 x 55 Swiss when fired in the Sturmgewehr 57 or PE 57 (semi-auto version). It has to do with the chamber shape and a feature having to do with full auto fire in the Stg. 57. The feature was retained in the PE 57 for ease of manufacture (not having to make two types of barrel). Its why I never bought one of the rifles - I couldn’t practically reload for it. Jack Dunlap, a local Luger collector well known at the time (died about 35 or 40 years ago) fired a 9 mm para by mistake in a Borchardt. He was trying the 9 mm in the chamber and had and accidental discharge. It was interesting to see. The bullet was extruded out and looked somewhat like a RN .30 rifle bullet. The case ejected from the gun with no apparant damage to it or the gun.

Interesting stuff.


#8

Regarding these cases as having been fired in an incorrect chamber, I wouldn’t think so, as all of the cases were found within a few feet of each other. And half of them had no such swelling above the extraction groove. I suppose the shooter could have had two guns, but what other centerfire chamber would allow that without fire-forming the case body into a completely different shape? Only one possible caliber that I can think of would be a .32-20. But, even if .30 Carbine would fit into a .32-20 chamber and could be fired, I’m not sure even that wouldn’t be obvious from the fired case.

By excess headspace, I mean the distance between the bolt face to the casing seat in the chamber would be too great. Insufficient headspace would not allow chambering with the bolt in a locked position. In any event, why would some cases have the bulge and some not, if all had been fired in the same chamber? All cases had the same HS. About the best I can think of is firing occurred in a Carbine without the bolt completely closed and locked, and I can’t imagine how that would happen.

Regarding squeezing down bullets of an incorrect caliber, I seem to remember in Hatcher’s Notebook a story about his firing .45 ACP ammunition in a Springfield '03, resulting in long, skinny .30 bullets emerging from the muzzle. And no ill effects on the rifle.

I sliced one of the cases. Here’s what it looks like on the inside. Amazing the head did not separate:

.


#9

Dennis

Without any more information, we’re only guessing. The good and the bad cases could have come from two different rifles, for all we know.

Short headspace would leave the head of the cartridge hanging out of the chamber, unsupported, causing it to bulge, at worst to rupture, and at best leaving what looks like a belt or rim. With excessive headspace, the cartridge would be seated deeper in the chamber.

If the chamber was cut for a rimmed cartridge of nearly the same length as the .30 Carbine, a Carbine cartridge would seat and fire and the head expands to form a rim.

I’m like you. I don’t see how a Carbine could fire a cartridge that’s not fully seated unless the firing pin was broken and frozen in place. The carbine design simply does not allow the firing pin to go forward until the bolt turns and locks in place.

Interesting cases, either way. It never ceases to amaze me what you can find at a public rifle range. I’m a very conservative shooter and when anything unusual happens, I will stop immediately. Others will shoot several more times just to see if it keeps happening.

Ray


#10

In your first case I find it incredible that the gun even survived. I would have thought that the 9mm bullet trying to force its way through the 7.63mm bore would be sure to cause catastrophic damage to the firearm.

In the case of the 6.5 Arisaka, do you mean that the chamber was simply re-cut for .30-06 and the bore left as 6.5mm?


#11

I wonder if the Chinese ammo and corrosive Berdan primers are part of the equation.


#12

John, I am sure it was fired in a 7.65mm Mauser. When I got home I stood the double shoulder case-which was clearly headstamped 7mm Mauser-next to a 7.65mm Mauser case. The “top” shoulder was exactly at the casemouth of the 7.65mm round, and from this “top” shoulder down the case was identical to the 7.65mm case. The top end of the 7mm case had obviously gone into the bore of the 7.65mm barrel and on firing had resulted in a “second” shoulder where the 7mm neck had expanded to fill the chamber the 7.65mm neck should be. I can’ imagine what the shooter thought about the accuracy of the 7mm bullet that instead of engaging the rifling, it bounced from side to side down the barrel!

Falcon, as John mentioned. This is not an uncommon occurrence. It was once speculated that the 8,15mm Mauser pistols-a few are known, see Geoff Sturgess’ article in the Journal- were actually 7.63mm pistols that had enough 9mm ammunition fired down the barrels to open them to 8.15mm. This has been shown to be untrue.

The 6.5mm rifle story dates back to the early 1960s. The shooter bought a Japanese rifle that he thought was 7.7mm when it was actually 6.5mm. Since it was very difficult to obtain hunting ammo in 7.7mm Jap back then, he obtained a 30-06 chamber reamer and opened the chamber to that caliber with no changes in the barrel. He had lots of success hunting with the weapon and fired a lot of 30-06 ammo through it. When a gunsmith finally looked at it he reckoned it was probably ready to blow up on the next shot and it got donated to the NRA museum-where I saw it many years ago. The NRA had it inspected and X-Rayed and found no cracks so they fired it extensively-and remotely of course-and tested it again. Still no evidence of damage.

The Japanese rifles from Pre-WWII and at least the early years of the war were probably the strongest Mauser action rifles ever built. In the 1950s and 1960s, they were prized for making hunting rifles for the Short belted magnum cartridges that would fit the magazines. At least they were prized by the gunsmiths in Wyoming.

Cheers,
Lew


#13

I have examined 9mm cases similar to the above 30 Carb which were fired out of battery.
Looked like a 9x19 belted.


#14

The story of the gent rechambering his 6.5 m/m Arisaka to .30-06 is even goofier than it seems at first. Since the reamer had a pilot to fit a .30 caliber bore, he found it necessary to turn the pilot down to fit the rifle’s 6.5 m/m (.256 in.) bore. You’d imagine that would have put him on his guard. But no, it didn’t. Jack


#15

It’s a good job that the guy with the 6.5mm/.30-06 never tried firing a round of steel cored M2 AP. That could have been messy.

XPH2USN: That’s a good point. The sectioned .30 Carbine case is actually a Chinese made round with a Berdan primer and fake L C 52 headstamp.


#16

Here are some 9mm Luger cases fired in a colt SA 9mm carbine. The reloader had used heavy .357" lead bullets in developing Sub-sonic loads. The long over sized lead bullet would some times not chamber smoothly and the extractor would jump over the rim and the FP would inertia fire the primer before full chambering. The hammer never dropped. Case wall adhesion kept the breech from blowing open. Most rounds fired fine but when the gun doubled, this was what the cases looked like. As Ray said, we don’t know what happened here but the head of the cartridges in the OP show a standard .30 carbine breech cone. Slam firing can and does happen with this weapon and improper cartridges (mostly reloads) are often to blame. Just my .02. JH


#17

Having used the M-1 Carbine extensively in my youth and having reloaded thousands of rounds for it, this looks like the rifle was firing out of battery. The upper part of the “belt” on these cartridges is the shape of the chamber end of the barrel. I suspect a frozen or very sluggish firing pin, likely caused by rust from firing this corrosive primed Chinese ammunition in the past and not cleaning… In my blissfull youth of handloading for the Carbine, I wore the brass out from too many reloads. I only realized that there was a problem when the cases were bulging severly and having nearly seperated case heads. The Carbine case is pretty strong.

That half of the cases found were normal suggests that initially the firing pin was frozen, and after what was possibly a burst of full-auto slam fires, the firing pin worked loose and the weapon fired normally after that. Or vice versa, the first rounds fired normally and then the firing pin broke/got stuck and the shooter stopped after noticing a problem with the weapon slam-firing.

AKMS


#18

[quote=“AKMS”]Having used the M-1 Carbine extensively in my youth and having reloaded thousands of rounds for it, this looks like the rifle was firing out of battery. The upper part of the “belt” on these cartridges is the shape of the chamber end of the barrel. I suspect a frozen or very sluggish firing pin, likely caused by rust from firing this corrosive primed Chinese ammunition in the past and not cleaning… In my blissfull youth of handloading for the Carbine, I wore the brass out from too many reloads. I only realized that there was a problem when the cases were bulging severly and having nearly seperated case heads. The Carbine case is pretty strong.

That half of the cases found were normal suggests that initially the firing pin was frozen, and after what was possibly a burst of full-auto slam fires, the firing pin worked loose and the weapon fired normally after that. Or vice versa, the first rounds fired normally and then the firing pin broke/got stuck and the shooter stopped after noticing a problem with the weapon slam-firing.

AKMS[/quote]

I agree… I would be checking the firing pin.


#19

There is one other possibility. Later production Universal carbines reduced the cam shoulder on the bolt that is supposed to prevent an out of battery ignition from happening. Two such guns that I examined had no cam shoulder at all. I know of at least three cases of Universals being damaged by case heads bursting and have heard of several more. I think they were trying to reduce costs but I will not fire any of the later Universals myself and do not recommend them to others. they are the versions with the open cam slot in the carrier and dual recoil springs. Earlier Universals used GI parts and are fine but the redesigned ones have been trouble prone in my experience.


#20

“The sectioned .30 Carbine case is actually a Chinese made round with a Berdan primer and fake L C 52 headstamp.”

I have been off this topic for awhile, but I did go back to look inside of one of my “Belted” .30 Carbine LC 52 cases. Sure enough, it has a Berdan primer. So what’s the full story on Chinese LC 52 headstamps? I have not heard of that one before.