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View Full Version : What happened here? (M2HB)


sir9usr
06-01-2012, 4:56 PM
Decided to take out the semi M2HB since it's been about a year since I last shot it.
http://i1097.photobucket.com/albums/g356/flea70/fleaM2HB.jpg

Checked headspace with the "Go-NoGo" gauge and all was good. Fired about 30 rounds when this happened...
http://i1097.photobucket.com/albums/g356/flea70/50bmgdouble.jpg

I'm figuring that once the round was fired, the empty case somehow separated while the bolt was still traveling rearward and it chambered a new round into what was left of the split case (the round in the rear is still live). Thankfully the extractor of a M2 is fairly robust so I was able to extract both(?) rounds easily.

For the life of me, I can't remember where I purchased the reloaded ammo (3-4 years ago) I either mail ordered it or picked it up when I went to Vegas GS (I know - reloads=problem #1). The brass is stamped LC 07 (Lake City) and was loaded with a 750 grn AMAX bullet. It's pictured on the left next to a TW45 (Twin Cities?) brass round fired last year. If you look at the base it definitely looks like its rubbing/stretching.
http://i1097.photobucket.com/albums/g356/flea70/LCTWsidebyside.jpg

The LC casing is distinctively taller than the TW case so I'm thinking the brass is too thin for an AMAX bullet? (even the shoulder looks longer) or am I losing headspacing? The problem is that the "Go-NoGo" Gauge is only a bar that measures between the bolt face and the barrel breech...(doesn't measure true headspace). I just picked up a Lee 50 bmg press so should I trash the LC casings?

http://i1097.photobucket.com/albums/g356/flea70/50bmgsidecomparo.jpg

Thanks in advance for any advice!

russ69
06-01-2012, 5:47 PM
Case head separation. This is caused by two things, brass that has been reloaded too many times or excess headspace. Measure for excess headspace first.

sir9usr
06-01-2012, 10:45 PM
Thanks Russ69 - looks like i'll need to invest in a set of true headspace gauges. A spare barrel might also be a good idea...

jfwlb
06-02-2012, 3:57 PM
WOW
I have shot the Ma Deuce for over twenty-five years while in the military and have never seen or heard of that happening before.

Quick question: when you said you checked the head space, did you just check it, or did you also adjust the head space using the barrel-click method? I have seen many dumba## privates either not adjusting it or getting it wrong when checked by their Sgt.

I have even seen a barrel fly out of the front when the charging handle was racked because somebody did not remember to actually screw in the barrel.

I hope you resolve your problems, the M2 is my favorite weapons platform.

John

Army
06-02-2012, 4:49 PM
The "soft", brighter ring is case head separation in progress.

The standard GI headspace gage is perfectly fine for any use. Remember to not cram either end in, only moderate pressure is needed to slip the go side into the face, it should NOT simply slide in easily. Make sure the firing pin is cocked, so as to get a full gage reading.

Also make sure your barrel lock spring is indexing tightly. If it's slipping under fire, headspace can grow very fast.

m35a2
06-02-2012, 8:15 PM
Seen that with LC once fired brass. I frequent a crowd that has semi M2HB and bolt rifles. About 2 years ago we came across a boat load of once fired brass. it was cleaned, sized and loaded. When we went out, the first two or three went off w/o a hitch, then there was a stuck case. Took the toy apart, got the case out, re assembled, head spaced and went at it again. 2 or 3 later, same thing. I don't remember how we figured it out, but we re linked non LC reloads and all was good. On another outing, another set of LC was put through the toy and broke a case after a few down the pipe. When we got home, the brass that wasn't reloaded was inspected. The cleaned brass showed a ring apx 3/8 inch up from the base...right where the case seperated after firing. This wasn't figured out in a day at the range, it took a few times out to gather the info. Since that was figured out, no LC once fired have been used, WC and Brit stuff is OK in the semi. The LC stuff is OK in a bolt though, just not a belt fed.

ojisan
06-02-2012, 8:25 PM
The shinier ring about 3/8" up from the head is where the brass is stretching.
If you look inside the case you will see this is right where the thickness of the case head and shoulder transition into the thinner straight sidewalls of the case.
If you can't see insside the case, you can take a paper clip and bend over the end a little to make a tip, you can drag the tip inside the case from bottom to top and feel where the case is belling out inside.
This can be a sign of too much headspace or simply that the case usefull life has been reached.

huckberry668
06-02-2012, 8:58 PM
I have first hand experience with this exact problem and it's not the case life or 'headspace' issues. It's over-sized chamber diameter. When the diameter of the chamber is too large it allows the brass to expand too much laterally. The momentum of the expansion pushes the brass at a high rate of speed and cuts up against the edge of the chamber. that's why you see the bright ring at 3/8" above the extractor groove.

Here is how I know.. a few years back I started a project to accurize FN-FAL rifles. I designed a barrel nut and a new barrel contour and modified a tube hand-guard to free float the barrel. Douglas cut 2 fully chambered XX barrels for me. I was able to set the heads-space to dead zero on a 'Go' gauge since it used a barrel nut design. I then indexed and drilled the gas port and put an Israeli heavy barrel gas block on.

With new ammo I got the same bright ring like yours on every round and 60% to 70% case head separation on once fired brass. I took apart the gun and compared it to surplus barrel and the only difference is the chamber internal diameter. Several surplus barrels that didn't have this problem had chamber diameters about .007" smaller than the Douglas.

Douglas took the barrels back to look at them and told me the chambers were way out of spec. If you can take the barrel off, measure the ID.

CSACANNONEER
06-02-2012, 9:41 PM
Uh, sorry Huck,

This is typical of a case that has been reloaded too many times or bad headspacing. I've seen the same thing
happen many times. I've seen it happen in match chambered 50s with in spec chambers. Since it obviously has not been an issue for the op before, suggesting that its due to an out of spec chamber doesn't make any sense.

sir9usr
06-02-2012, 10:29 PM
Thank you all for your replies - I figured someone on here has had experience with this. I never even considered the barrel lock spring slipping which I'll look into. When I check headspace, I screw the barrel in all the way until it stops and then back it off about 2-3 clicks and check it repeatedly with the G-NG gauge. In the meantime, I'll try to measure the chamber end to see if it's out of spec. Time to scrap the LC brass...

The Gleam
06-03-2012, 3:50 PM
Uh, sorry Huck,

This is typical of a case that has been reloaded too many times or bad headspacing.

I agree to the same, but suspect reloaded too many times. Check headspacing again anyway, but the ring, the unknown reload, etc., seems likely to be once reloaded too many.

huckberry668
06-03-2012, 8:12 PM
I agree to the same, but suspect reloaded too many times. Check headspacing again anyway, but the ring, the unknown reload, etc., seems likely to be once reloaded too many.

I figure that's the most obvious since he said it was reloaded and everyone already jump on that so I didn't bother. It didn't make any sense to me when it happened to me either. Took me a couple of weeks to diagnose. I figured I'd share another rare possibility since my head-space tolerance was .000" and it still happened.

CSACANNONEER
06-04-2012, 11:26 AM
I figure that's the most obvious since he said it was reloaded and everyone already jump on that so I didn't bother. It didn't make any sense to me when it happened to me either. Took me a couple of weeks to diagnose. I figured I'd share another rare possibility since my head-space tolerance was .000" and it still happened.

I, for one, appreciated hearing about your experience. But, I think it is a lt less common and couldn't be possible in the OP's case. Since, he has fired the gun many times and an out of spec chamber would have shown itself long ago. However, it is very common, even with brand new ammo, to have this happen in FA M2s.

Army
06-04-2012, 4:39 PM
... However, it is very common, even with brand new ammo, to have this happen in FA M2s.
Wait, this is a FA M2?

Re-do your timing! Every time you swap barrels or change the headspace, re-check the timing also.

Separation like this can happen when the bolt is not totally forward before the firing pin is release, or it is already moving to the rear before chamber pressure has fallen enough.

Severe out-of-time can result in an out of chamber detonation when that case head gives way long before the bolt is forward. Pretty "exciting" when your gun goes skyward as that grenade goes off between your legs :)

CSACANNONEER
06-04-2012, 4:56 PM
Wait, this is a FA M2?

Re-do your timing! Every time you swap barrels or change the headspace, re-check the timing also.

Separation like this can happen when the bolt is not totally forward before the firing pin is release, or it is already moving to the rear before chamber pressure has fallen enough.

Severe out-of-time can result in an out of chamber detonation when that case head gives way long before the bolt is forward. Pretty "exciting" when your gun goes skyward as that grenade goes off between your legs :)

No, the OP's gun is semi. I was just saying that case head seperation is not uncommon in any M2. When we started sending kids back into the sandbox a few years ago, I heard that more than a few top covers got blown off because, no one was teaching them how to maintain the gun, time and adjust the head space it properly. I've seen a lot of once fired MG brass which was fired from M2s with so much head space that the brass was trash and couldn't be reloaded again. In fact, I bought 4000 rounds like that about 18 months ago.

Army
06-05-2012, 4:15 PM
Ah, took your response wrong. Thanks :)

CSACANNONEER
06-05-2012, 6:06 PM
Ah, took your response wrong. Thanks :)

It was poorly worded. I was/am still tired from a FCSA match this last weekend.