Why proper M2 .50 cal headspace is critical


April 27, 2005, 04:18 PM

Apologies if this has been posted before.

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Dave R
April 27, 2005, 04:27 PM
Haven't seen it before. Not for the bandwidth-challenged.

Something I don't understand. It looks like 2 shots are fired, and then the kaboom occurs, without the action cycling again. Did it cycle and then fire prematurely? Otherwise, I don't see how it happened.

April 27, 2005, 04:33 PM
I agree. There's a long pause after the second cycling.
The movie is running very slowly though, so it's hard to get a good idea of timing.

I think anyone near that would not be a happy camper though. :eek:

Texian Pistolero
April 27, 2005, 04:47 PM
Not sure, been thirty years since I headspaced a Ma Duece.

Two much headspace, and you have an unsupported case, hence fractured fairy tale.

April 27, 2005, 05:12 PM

April 27, 2005, 05:30 PM
I think I still remember that the M2 has to cocked twice to get the first round in the barrel.

April 27, 2005, 05:33 PM
It didn't fire twice, it takes two strokes of the charging handle to chamber a round and that is what you are seeing.

I've seen this happen in person once, carnage but the guy lived minus one testicle and LOTS of scars.

It usually is the result of someone over confident not using the guages, or by someone tweaking it for a little more rounds per minute and getting caught. Set them up loose and they shoot faster, set them tight and they are a little slower but there are limits.

Texian Pistolero
April 27, 2005, 06:36 PM
Actually...the drill is...VERY SIMPLE....

but you DO.....have to DO...... it RIGHT.


April 27, 2005, 08:25 PM
I'm guessing they expected failure to occur... Did they SAY that it was excessive headspace? I'd almost think a plugged barrel or a hot round.

April 27, 2005, 09:14 PM
That's why you are supposed to fire that pig from INSIDE the tank! :D

April 27, 2005, 11:19 PM
I've seen this happen in person once, carnage but the guy lived minus one testicle and LOTS of scars.



April 28, 2005, 03:07 AM
Holy crap. :eek:

April 28, 2005, 08:38 AM
Over-charged round?
Squib round for shot 1?
Round charged with c-4 sted of normal powder?

cracked butt
April 28, 2005, 08:43 AM
Other than the huge amount of hot gas given off, the gun looks like it held up pretty well, at least to my novice eyes. Mr. Browning designed good stuff. The guy standing next to or behind the gun might not hold up so well though.

April 28, 2005, 09:12 AM
Interesting - but I wonder if there's any significance to the date that's shown at the beginning?

April 28, 2005, 09:31 AM
Troops in Iraq are destroying several M2's per week due to improper headspacing (you have to headspace the M2 every time you get ready to use it). The video is meant as a training film to show the troops why following the TM to the letter is very important, forgetting one step (I think its pulling back the charging handle) will cause excessive headspace as in the video. It was taped at Rock Island Arsenal by the US Army. All of the above I discovered while reading the thread about the video at ar15.com in general discussion, but I cant find the thread again (even searched for all sorts of words I thought were in the title).


April 28, 2005, 10:17 AM
There is just short of two ounces of jacketed bullet and about 240 grains of powder in every 50 BMG round. That is not a live round on a squib, or C4 or anything like that. The power of the 50 is hard to believe if you haven't been around them, figure about 12,500 lb/ft of energy for a standard ball round!!!!!! Compare that to 350 for a 45 acp or 2600 for a 308, BIG difference.

A blown case from excess headspace in the M2 is basically a casehead separation, so all of the hot gasses and metal being blown out come out in all directions after the extractor gets cut/blown off. The bottom is open and that is where the really dangerous parts and pieces are blown out, if you are standing behind it shooting it you are in trouble.

Most barrels want to be 5-9 clicks out from threaded all the way in, and you can just spin them in and back them out say 7 and be fine on a gun you know with barrels you know. BUT, if there is a little piece of crud on the threads or something and the barrel stops 10 clicks short of true bottom, then you come out 7 you had BETTER be using the gauge or you WILL blow it up. It only takes two seconds to check the headspace.

April 28, 2005, 10:42 AM
We had the gauges right on the side of the main control panel where the TC sits in a little crown royal bag. :)


April 28, 2005, 01:25 PM
Looks alot like the engineering range at FN Herstal. The charging handle gonculator is typical Herstal.

April 28, 2005, 01:50 PM
The charging handle gonculator is typical Herstal.
I never knew there was a technical term for "remote-controlled charging handle puller thingie". :o


Sergeant Sabre
April 28, 2005, 01:54 PM
Over-charged round?
Squib round for shot 1?
Round charged with c-4 sted of normal powder?

There is NO shot #1. What you are seeing is the device pulling the bolt back, locking it, and then releasing it. The "Clank" you hear is the bolt slamming home. First on an empty chamber, then on a loaded one. When you insert ammunition into the feed tray of an M2, it takes TWO pulls if the charging handle to chamber a round. That's what's happening here.

April 28, 2005, 01:56 PM
"All, Please take a moment to look at this short video clip and feel free
to use it for training, etc...it was put together by one of our Senior TACOM
Small Arms Equipment Specialists at Rock Island who operated our Small Arms
> Support Center(SASC)in Balad, Iraq; essentially a "mini Depot" repair
> facility for all Small Arms...his comments are below.
> USAMC LAO Ft Riley
> This was done at the XXXXX here at Rock Island to re-create the
mistakes that continue to occur in Iraq. The troops screw the barrel into
50 without pulling the bolt back to release the locking spring. They
then loosen the barrel up 3 to 4 clicks and attempt to fire it.
> I would see between 5 to 8 of these guns a week at the SASC in Balad.
> It destroys the gun, and can injure the soldier."

5-8 a week, god damn.

April 28, 2005, 02:10 PM
Ah, yes, gonculators. The first known use for the word gonculator was at Smith & Wesson. "Gonculators" was a jargon/slang term for the handheld computers used during the semi-annual physical inventory.


Owen: "Hey Timmah, Did you see all the gonculators next to the pistol office?"
Brett: "Yeah, physical inventory is next week"
Owen: "Darnit Timmah, I hate using those gonculators!"
Brett: "HAHA, I never have to do inventory!"
Owen: "That's because you were raised by wolves and can't count!"
Craig: "Owen, can't you see Brett is doing something useful? Go back to your desk before I banish you to the range, and make you shoot .44's all day!"

Owen scurries out...

Later on, a young engineer named Owen started to use the term gonculator for any random doodad. He has spread the term through several gun companies, much as Typhoid Mary spread, uh, typhus. Apparently all of these companies have overcome the infection.

April 28, 2005, 05:30 PM
That charging assembly is the one used for the M296 model of the .50 cal. This is the model used in a gun pod configuration on the OH-58D Scout helicopter.

How do I know this you may ask? I work on them daily! Yes, if headspace is not set right very BAD JUJU! Makes pilots say bad words to the ground crew. :cuss:

At least when this model is used, there is no one actually holding on to the weapon.

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