Why rifle safety features are important - AI-AW50


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Zak Smith
May 24, 2010, 01:16 PM
A couple other SnipersHide members and I went out Sunday morning for some extreme long range shooting. There were two AI-AW's present: a GAP-barreled .260, and a factory .308; one AWSM in .338LM, and one AW50. The wind was real bad, but we were able to put a bunch of hits on a target WAY out there - we estimate 1600 or 1700 yards based on the dope we needed to apply to hit it.

We were shooting some 750gr AMAXs through the AW50...
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4862_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4862_img.jpg)
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4874_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4874_img.jpg)

... and at some point noticed this ...

http://demigodllc.com/photo/PAWNEE50/smaller/D463_4881_img_c2.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4881_img_c2.jpg)

Hmm, that's the pressure release "valve" (really a plastic disk) that covers the two vents from the bolt area. The AW50 has one such vent on either side of the receiver to safely vent pressure away from the shooter if there is a case rupture. Hey, wait, did that just fall out or something? Weird.

Well I was convinced that it couldn't have just fallen out, so I started to look through the fired brass and here's what I found:

http://demigodllc.com/photo/PAWNEE50/smaller/D463_4881_img_c.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4881_img_c.jpg)
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4881_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4881_img.jpg)

So there was a gross defect in one of the LC cases. At some point we shot that round and didn't notice anything different - except it was almost certainly one of the "misses" - and kept shooting. Neither the shooter or observers noticed anything different at the time, nor did it affect the ability to make hits after the bad round (maybe 5 or 10 more rounds were shot until we noticed).

Being able to take a ruptured case head while igniting over 230gr of powder, make the condition safe for the shooter and not even noticeable at the time, and continue shooting accurately is a very strong testament to the engineering and design that went into this gun. In a lesser gun, this failure could have caused serious injuries and rendered the rifle inoperative.

When we went over the footage later, we actually found the footage of the bad round:

http://www.youtube.com/watch?v=257Du_JrCGg

And the obligatory "group" photo

http://demigodllc.com/photo/PAWNEE50/smaller/D463_4855_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4855_img.jpg)

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mregunz
May 24, 2010, 03:03 PM
Yep no dought,Safety is very impotant and goos construction on like the mod. 770 rem.And it has some serious safety features I belive I certianly,wouldn't shoot full house max reload 's in it.43,000 saami or less presure.The lug's are way to small,the press fit barrel,and the 2 piece bolt all big red flag's for weak link's I think.And in the early 1900's when 03 came out the military discovered the 2 piece firing pin was a weak link in the gun.So I belive a 2 piece bolt is just as bad....GOOD SHOOTING,Good Hunting .Those are some mighty fine.lookin rifles

R.W.Dale
May 24, 2010, 03:13 PM
Yep no dought,Safety is very impotant and goos construction on like the mod. 770 rem.And it has some serious safety features I belive I certianly,wouldn't shoot full house max reload 's in it.43,000 saami or less presure.The lug's are way to small,the press fit barrel,and the 2 piece bolt all big red flag's for weak link's I think.And in the early 1900's when 03 came out the military discovered the 2 piece firing pin was a weak link in the gun.So I belive a 2 piece bolt is just as bad....GOOD SHOOTING,Good Hunting .Those are some mighty fine.lookin rifles
HMMMMM

you do realize that the rem 700 uses a THREE piece bolt.


Neat report Zack!!! Could you post a pic of the plug in question in place for comparison

Zak Smith
May 24, 2010, 03:17 PM
You can see it in the first two photos.

R.W.Dale
May 24, 2010, 03:19 PM
Ah! You most certianlly can.

Carry on

1858
May 24, 2010, 03:43 PM
you do realize that the rem 700 uses a THREE piece bolt.

Not necessarily .... :D ... bolt handle designed/made/indexed/TIG welded by me. Bolt made by Pacific Tool and Gauge. All three of my Remington's have these one-piece bolts now.

http://128.171.62.162/hawthorn-engineering/thr/rem700_308win/photos/308_bolt_pt&g.jpg

http://128.171.62.162/hawthorn-engineering/thr/rem700_308win/photos/308_bolt_pt&g_2.jpg


Zak, how many times have those LC cases been reloaded? You mention 230gr of powder and 750gr A-MAX bullets so I'm assuming that they're reloads. Also, you state "there was a gross defect in one of the LC cases" so are you basing this on the fact that the fracture was parallel to the length of the case (axial failure because hoop stress is 2x axial stress)? A case failure due to case head separation (overworking of the brass) would be radial. Just wondering about your thought process but excellent post and superb photos as usual.

:)

Zak Smith
May 24, 2010, 03:49 PM
Hi,

The LC cases were supposed to be once fired when I got them, and none of those had been fired more than once by me since then - so this case had either one or two firings only. It was "over 230gr", so one can probably guess what load data I was using for match reloads.

I say it's a gross defect because of the failure it caused and the history of the cases. The best explanation I can offer is that there was a weak spot in the brass due to some unknown factor. I do not believe the brass was worked excessively based on its history. I think I will cut the brass open to see if I can determine anything else about it.

1858
May 24, 2010, 03:49 PM
Zak, in the second to last photo there's another red "plastic" plug in the bolt ... is this also a pressure relief port?

:)

Zak Smith
May 24, 2010, 03:50 PM
Yes, all the red ones are that.

1858
May 24, 2010, 03:54 PM
Yes, all the red ones are that.

Hopefully the ones used by the British military are multicam versions .... that big red dot could stand out on a dull day! :D Maybe next time you can get both plugs to pop out ... good luck with your brass inspection and please post the results if you feel so inclined.

:)

Zak Smith
May 24, 2010, 03:55 PM
No kidding. I am good about inspecting brass while prepping it so I am pretty sure there was no visible indication of this weak point.

mregunz
May 24, 2010, 04:10 PM
Krochus,my 700 might have a 3 piece bolt,but if it does there isn't abig gap where the head is pinned on the bolt.and the lug's on mine I measured Are7or8 times more surface lockin in the action than on a junk 770.And if ur countin the brazed bolt as a 3rd piece.I don't think that really count's as far as a 3 piece bolt.And I'am not sure my 700 has a even a 2 piece .I'll ask my gunsmith.And if it does It's 100 times sounder and better put together than a junk 770.

TexasRifleman
May 24, 2010, 04:14 PM
Just curious, is that a part that would normally be carried as a spare or was this a surprise to actually need another one?

I assume there's some reason for not leaving the hole open all the time or is it covered just to keep gunk out?

Very interesting stuff, thanks for posting it.

Zak Smith
May 24, 2010, 04:21 PM
I believe it's just to keep stuff out of the action, since it opens to where the back of the barrel meets the front rim of the bolt. Also, in conjunction with the safety ports themselves, their absence indicates something bad happened. Per AINA's insistence, I will be sending the rifle to them so they can check all the parts exposed to gas for potential gas erosion. I would be very very surprised if anything needed to be fixed.

Maverick223
May 24, 2010, 05:57 PM
Bummer, but I wouldn't want to risk the possibility of loosing the warranty by not complying with their request. I am certain all will be well though, that is one massive pressure relief port (or valve as they erroneously term it).

:)

Dave Markowitz
May 24, 2010, 06:37 PM
Good example of why one should always wear eye protection. Not all actions handle escaped gas that well.

Zak Smith
May 24, 2010, 06:42 PM
I don't know if they call it a valve or a port or what -- I've never seen an official parts diagram.

Malamute
May 24, 2010, 09:57 PM
I had a similar thing happen shooting a 1903-A3 Springfield (made by Remington) back in the 80's. I was shooting FA 28 rounds I believe. 1928 to be sure tho. I didn't notice anything happened until I had picked up brass and saw the hole in the base similar to yours. It was factory ammo. I always wondered if it was just a bad case, or if the brass had somehow weakened over time. I "saved" the rest of that ammo after that happened tho.

Maverick223
May 24, 2010, 10:07 PM
Brass doesn't normally degrade over time, but I am unsure if the corrosive primers would degrade the brass (I think it might). Better send it to me for proper disposal. :D

rodinal220
May 24, 2010, 10:13 PM
Do you know if the LC brass was fired through a M2 Browning??I wont use MG brass because M2s are known for being hard on brass due to M2s having generous head spacing.This could explain the incipient head failure.Most onced fired .50 brass has been fired in a MG.


I only run virgin .50 BMG brass in my bolt gun.If you have a hard time finding virgin brass and are forced to use MG brass inspect the brass carefully.Use a simple wire tool like the one on this link to check for incipient head separation.

http://www.hevanet.com/temple/50reloading.html

Wes Janson
May 24, 2010, 10:31 PM
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4881_img_c.jpg

There does definitely appear to be radial stretch marks on the web of that case, near the top of the rupture. To my (untrained) eye, it appears that the gas first escaped at the forward end of the split, and then vented/cut back towards the rear as it flowed out of the case. Once-fired .50 BMG brass is invariably sourced from beltfed Brownings, generally M2HBs, and has typically been stretched out considerably in excess of what a normal bolt-action chamber would permit.

Personally, I've probably had close to a dozen full-blown case head separations in my M3HB, and they're little more than a minor inconvenience as long as you have a case extraction tool. Long term cumulative effects of the gas pressures over larger number of rounds are unknown, but my chamber and bolt suffered no ill effects. Incidents like this are why many .50 BMG reloaders suggest to inspect the insides of fired cases for the beginnings of a separation ring.

1858
May 24, 2010, 10:57 PM
This could explain the incipient head failure.

If the case has failed it's not incipient is it!

A cylinder under pressure (with no defects) will always fail due to hoop stress and not axial stress. Hoop stress is 2x the axial stress and failure due to overpressure will result in a crack that runs parallel to the long axis of the cylinder. In Zak's case (no pun intended), the crack is significantly longer in the direction parallel to the long axis of the case. Incipient case head separation manifests itself as radial thinning of the case wall (near the case head) which typically results in an annular separation. I don't think you can assume a case head failure here due to excessive head space.

:)

Zak Smith
May 24, 2010, 11:05 PM
Hi,

I don't know the ultimate origin of this piece of brass. I prefer to use either brand new brass or once-fired brass that has been fired in something other than a MG-- however, at the time I loaded this ammo I had some LC ready to go. If I come across a case that does not easily full size, I throw it out. From now on, I may use *only* brass in those preferred categories and sell off the LC. Who knows. We'll see how it cleans up.

Looking at the case in person, I don't see stretch marks that are very out of the ordinary for cases fired in a bolt gun. I do see a ring at the top of the web where the body of the case has expanded to fit the chamber, then tapering down as the web thickens.

What I find interesting about the external appearance of the rupture itself is the powder pattern. In the quoted photo, just under the (C), there is no powder fouling trace for about half the length of the slit. It looks like the gas flowed mostly clockwise out this slit, at least opposite the spot lacking fouling.

Anyway, I hope to find out more when I section the case.

Thinking about what 1858 wrote about hoop stress, I wonder if the web area was either undersized (and thus had less chamber support) or was weak in this case (or in this area) for some reason, ie, a defect.

1858
May 24, 2010, 11:20 PM
What I find interesting about the external appearance of the rupture itself is the powder pattern. In the quoted photo, just under the (C), there is no powder fouling trace for about half the length of the slit. It looks like the gas flowed mostly clockwise out this slit, at least opposite the spot lacking fouling.

I would add that the 90 turn at the end of the slit is where the gas (or crack propagation) took the path of least resistance since the case wall starts to get thicker at the web.

:)

Zak Smith
May 24, 2010, 11:25 PM
I'll post more as I find out more about both the case itself and any effects AINA finds in the rifle. They did tell me that another rifle had something similar happen using c.a. 1950's brass and it toasted the chamber.

Now, where can I get a .416 barrel for my rifle... I know all that brass is new.

-z

JTW Jr.
May 24, 2010, 11:32 PM
Great picts , I place eye safety right up there with rifle safety features ;)

Maverick223
May 25, 2010, 12:26 AM
Just to fuel my curiosity, what is the date headstamp? Hard to tell, but it looks like "32", or is that an "82" (...or something else altogether)?

:)

Zak Smith
May 25, 2010, 12:29 AM
L c 82

Maverick223
May 25, 2010, 01:12 AM
Figured that much, '32 would be some mighty old .50BMG (though I have an old WWII AP round from 1943). Thank you for satisfying my curiosity.

:)

gunnie
May 25, 2010, 07:03 PM
Zak,

http://www.precisionshooting.com/psm_2010_01_issue.pdf

just a thought, trying to repay you for info you have dug up for itself in the past.

thanx again,
gunnie

Zak Smith
May 25, 2010, 07:47 PM
Good find! I just sent that to the printer for reading later..

briansmithwins
May 25, 2010, 08:30 PM
Not to be a dick, but why is your eye protection on your forehead?

Sure, they look cool up there but they certainly can't protect your eyes from that position.

BSW

Wes Janson
May 25, 2010, 08:49 PM
Not to be a dick, but why is your eye protection on your forehead?

Sure, they look cool up there but they certainly can't protect your eyes from that position.

BSW

I assure you that he's not about to fire that weapon.

You'd be hard pressed to find a photographer sufficiently obtuse to sit at that angle from a .50 BMG muzzle brake...

Zak Smith
May 25, 2010, 08:49 PM
Not to be a dick, but why is your eye protection on your forehead?

Sure, they look cool up there but they certainly can't protect your eyes from that position.
My eye protection was right where it needs to be - in front of my eyes. I wear eyepro 100% of time. You'll have to find the guy in the photo and ask him yourself; I can't answer for him.

Zak Smith
May 25, 2010, 08:50 PM
I assure you that he's not about to fire that weapon.
This is also true for that photo.

briansmithwins
May 25, 2010, 08:56 PM
You'd be hard pressed to find a photographer sufficiently obtuse to sit at that angle from a .50 BMG muzzle brake...

Well, not twice, anyway. I wasn't thinking about the angle...

I'm just sensitive about wearing eye protection as I've worked with a couple of people that were blind in one eye as the result of trauma.

We recently had a guy at a match get a fragment of rock in his lower eyelid from a berm hit. He was wearing his safety glasses and the rock fragment came in under the edge of the lens.

People often ask me (usually during the summer) if the goggles aren't hot. They are, but I like the full protection. BSW

http://i2.photobucket.com/albums/y3/briansmithwins/IMG_5966Medium.jpg

Zak Smith
May 28, 2010, 02:19 AM
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4899_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4899_img.jpg)
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4904_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4904_img.jpg)
http://demigodllc.com/photo/PAWNEE50/smaller/D463_4909_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4909_img.jpg)

Ratdog68
May 28, 2010, 02:30 AM
Yowzer !!! That takes some serious pressure to punch through there... thick walled, and a dished surface too.

Zak Smith
May 28, 2010, 02:37 AM
Here's the case head for comparison

http://demigodllc.com/photo/PAWNEE50/smaller/D463_4892_img.jpg (http://demigodllc.com/photo/PAWNEE50/?small=D463_4892_img.jpg)

This load is way under max so in conjunction with the head condition it is unlikely it was overpressure. My money is on freak case defect.

1858
May 28, 2010, 03:09 AM
This load is way under max so in conjunction with the head condition it is unlikely it was overpressure. My money is on freak case defect.

There isn't much comfort in that since it's impossible to predict or control "freak case defects" but AI has you covered (right?). A point defect would have to be a crack, pit (from corrosion) or inclusion but without further analysis you'll never know. Let me know if you want additional analysis done (no charge) using SEM and EDXA techniques. Regardless, it clearly isn't a case head separation issue so the question is, are you going to continue to use that lot of cases?

:)

gunnie
May 28, 2010, 10:17 AM
luckily, i just got my eyeballs recalibrated by the national standards institute (ANSI). my highly scientific observation (NOT) is the primer shows no signs of excess pressure. i'd be prone to roll with you ~and~ 1858. bad case, delete same lot brass.

gunnie

Zak Smith
May 28, 2010, 12:08 PM
One other general note is that the case wall thickness on the end part we cut off is approx 0.015" different from thick side to thin side, but the crack was not on the thin side-- it was halfway between the two.

1858,

No kidding. Impossible to predict case defects are kind of scary once you start to think about them! I'd love to get to the bottom of what caused the problem - please email or PM me privately and I'll mail you the cut-off case head.

1858 & gunnie,

I have a bunch more brass and the 82-83 LC is the minority, so I am planning to simply not use that brass anymore. I do have some more recent LC, some IMI, and some Barrett, so the question now is: Do I shoot even the more recent LC, or just stick with the IMI and Barrett brass that I know was not fired in machineguns?

-z

Maverick223
May 28, 2010, 12:20 PM
Do I shoot even the more recent LC, or just stick with the IMI and Barrett brass that I know was not fired in machineguns?Take this with a grain of salt, because I haven't a .50BMG, and my experience with one is limited, but understanding the stresses that the brass undergoes when fired from a M2 I would feel more secure with the IMI/Barrett stock that you have.

:)

Zak Smith
May 28, 2010, 12:23 PM
On the other hand LC brass is used extensively for all manner of .50 loads that are going to be shot in bolt guns, and reports of this type of event are very rare.

Boba Fett
May 28, 2010, 12:30 PM
Dang...didn't expect the case to be that thick.


Good to know some engineers somewhere thought of those rifle safety features though...


Good example of why one should always wear eye protection. Not all actions handle escaped gas that well.

+1




Beautiful rifles btw Zak.

Maverick223
May 28, 2010, 12:41 PM
On the other hand LC brass is used extensively for all manner of .50 loads that are going to be shot in bolt guns, and reports of this type of event are very rare.Have to agree with that too, you are unlikely to ever repeat the event, but why tempt fate? I would use what I had (excepting this lot), and use brass of known origin (not MG brass) henceforward.

Good to know some engineers somewhere thought of those rifle safety features though...Speaking of which, this thread is like an AISC convention, failures are like Engineer attractant.

:)

Zak Smith
May 28, 2010, 12:52 PM
In my real job I am a verification engineer, which - I half-joke to my wife - is about asking inappropriate questions to see what answers I get.

Maverick223
May 28, 2010, 01:22 PM
In my real job I am a verification engineer, which - I half-joke to my wife - is about asking inappropriate questions to see what answers I get.Hmm, suppose I just assumed that you were an ME, due to your suppressor business. We won't hold too much against you. :p

1858
May 28, 2010, 01:50 PM
1858, No kidding. Impossible to predict case defects are kind of scary once you start to think about them! I'd love to get to the bottom of what caused the problem - please email or PM me privately and I'll mail you the cut-off case head.

Zak, I just sent you a PM with my address. As I mentioned in the PM, I won't post the results but rather, I'll send you the data (images and spectra) and you can interpret and use the results in any way that you see fit.

As for the LC brass (both lots) ... hmmm ... I'd use it to make .50 cal windchimes and sell them on Ebay or load them up with a "pretty" bullet, no powder and a fake primer and use them as stocking stuffers!! Seriously though, how much LC brass do you have compared to the IMI and Barrett cases?


One other general note is that the case wall thickness on the end part we cut off is approx 0.015" different from thick side to thin side, but the crack was not on the thin side-- it was halfway between the two.

You mentioned that this sort of failure is unusual but you also mentioned that there was a difference in case wall thickness. I use a Redding Case Neck Gauge to measure case neck wall thicknesses. The theory is that an inconsistent neck wall thickness is indicative of inconsistent wall thickness througout the whole case. It would be interesting if you compared the LC brass to the Barrett or IMI using a similar tool. Redding recommends < 0.001" runout during one full rotation of the case neck.

http://128.171.62.162/hawthorn-engineering/thr/reloading/case_neck/redding_neck_good.jpg

http://128.171.62.162/hawthorn-engineering/thr/reloading/case_neck/redding_neck_bad.jpg

:)

Zak Smith
May 28, 2010, 02:09 PM
Maverick223,

I went to school for EE.

1858,

I have, well, quite a bit of more recent LC brass. I'll be in touch re: the analysis.

-z

1858
May 28, 2010, 02:39 PM
I have, well, quite a bit of more recent LC brass. I'll be in touch re: the analysis.

OK ... if you plan on keeping the LC brass I'd suggest that you measure the case necks and sort out batches based on neck runout. I'd start off by using cases with tight case wall tolerances (as inferred from the neck measurements). Maybe there isn't a good correlation between that one case failure and its inconsistent case wall thickness but at this point it's all you have. If after the SEM/EDX analysis a clear defect is observed then perhaps you can chalk it up to an anomaly and go about your business. The question is, what do you need to do to erase this failure from your mind every time you pull the trigger? You may be wondering if a case will explode in your face and you may also be thinking that you'll miss your target if a case fails.

:)

gunnie
May 28, 2010, 03:25 PM
1858,

he said the failure was about 90 degrees out from the thinnest point. if you want to check wall thickness beyond a shadow of doubt, make up a simple test fixture like the link in posting #30.

i searched for a copy of the original article i had read about this in. was an american rifleman circa '70's-'80's. the author also included a test for case head perpendicularity to center line, by centering neck bore on a ball bearing while locating case wall in a simple "V" block type set up, and indicating off of outer edge of the base beyond stamping indentions. said accuracy gains to be the driving force for its case wall usage, but case rupture prevention is a byproduct, though same seems non issue in Zak's case.

gunnie

Boba Fett
May 28, 2010, 03:31 PM
I went to school for EE.


My best friend is an EE working at Rockwell Collins.

EE and ME are fascinating to me....makes me wish I'd chosen one of those paths in college...ah well

At least I get to learn a lot about it from my friend.

1858
May 28, 2010, 03:59 PM
he said the failure was about 90 degrees out from the thinnest point. if you want to check wall thickness beyond a shadow of doubt, make up a simple test fixture like the link in posting #30.

gunnie, I realize that the failure was between the thickest and thinnest sections of the case (the transition region I suppose) but the point is that a case with inconsistent wall thickness has failed. Did the inconsisent drawing of the brass result in inconsistent work hardening? Maybe and maybe not.

I agree that the fixtures shown in post #30 are the way to go to be absolutely sure of wall thickness througout the majority of the case but I'd hardly call them "simple" even if you have access to a machine shop. The Redding Case Neck Gauge is readily available and fairly inexpensive as is the RCBS Case Master Concentricity Gaging Tool (see links below).

http://www.midwayusa.com/viewProduct/?productNumber=311160
http://www.midwayusa.com/viewProduct/?productNumber=310955

:)

gunnie
May 28, 2010, 08:27 PM
..."Did the inconsisent drawing of the brass result in inconsistent work hardening?"...

the simplest way to find this out would be to check wall thickness on the cases that didn't fail. dunno LC spec for thickness variation, but wouldn't be very surprised to learn that 15 thousandths is within max run-out.

gunnie

Zak Smith
May 28, 2010, 09:03 PM
I'll be shipping the failed case and another LC 82 case to 1858 shortly.

1858
May 28, 2010, 09:39 PM
dunno LC spec for thickness variation, but wouldn't be very surprised to learn that 15 thousandths is within max run-out.

Zak,
If you still have the rest of the failed case could you measure the neck wall thickness at 3, 6, 9 and 12 o'clock. It'd be interesting to see if the ratios are the same when compared to your earlier measurements of wall thickness near the case head. This is a rather obvious attempt by me to see if there's any real science behind Redding's Case Neck Gauge.

:)

gunnie
May 29, 2010, 11:09 AM
1858,

get a cheap-o mag base for your dial indicator:

http://grizzly.com/products/Flexible-Magnetic-Base-Holder-130-lb-Force/G9625

or, score a cheap-o indicator with it to save repeated indicator removal from your redding:

http://www.grizzly.com/products/Dial-Indicator-1-2-Range-x-0-00

bend about 1/8" dia round stock until it resembles the side profile of a folding knife belt clip. make sure the bend is enough to clear the offset from neck to case wall I.D. of your particular brass, and contact the round stock on the small radius that would be the initial contact point of above mentioned knife clip. make sure round stock is long enough to get to bottom of casing, just above webbing.

have a welder tack same onto disassembled flex neck lock handle of mag base. welding current could kill magnets. put lock collar back on mag base and bend flex-neck to where indicator plunger meets bent round stock just barely on the inboard side of interior contact radius of bent round stock. remember that the smallest reading you can obtain by moving the brass around will be the correct one.

not as easy to use as designated fixtures for this, but an inexpensive, accurate method for testing wall thickness. an added advantage to this will be the ability to test for unsafe thickness the full length of brass due to multiple reloadings. same will begin just ahead of base webbing due to brass flow from ignition pressures.

gunnie

gunnie
June 20, 2010, 08:37 PM
..."dunno LC spec for thickness variation, but wouldn't be very surprised to learn that 15 thousandths is within max run-out."...

i think i was way off with that statement. my thinking was untill the US purchased some barrett 82A1 rifles in 1990 for desert shield/storm, there was no real need for the 50BMG to be all that accurate, from a belt fed Ma Duece.

got two empties to test same theory. one was an LC 79 (pre 82A1) the other an LC 03 to cover the post 82A1 need for accuracy:

measured both with the transponder of an ultrasound thickness meter located in a holding fixture @ 5/8ths inch from base plate. turned both MANY times, recording all of the readings i got through entire circumference.

the LC 79 read 0.084-0.087---three thous. run out.

the LC 03 read 0.083-0.087---four thous. run out.

feel safe saying LC holds tighter tolerances for the 50BMG than i thought!!!

something very non typical with your failed case.

gunnie

gb0399
June 20, 2010, 08:53 PM
Maybe they should put a hole like that on this M4. Thats the bolt carrier peeled back. The round had a catastrophic failure. The upper and lower both bowed out. The floor plate of the mag blew out. The shooter was fine. Always wear your eye pro

SlamFire1
June 20, 2010, 09:01 PM
Brass doesn't normally degrade over time, but I am unsure if the corrosive primers would degrade the brass (I think it might). Better send it to me for proper disposal.

Powder sure does and it releases nitric acid gas which will cause brass splits. Usually first in the case neck area. But this brass is not that old.

As for this 50 caliber case, brass flaws happen.

Shooting bud of mine, he was using new LC primed cases in his M1a. He pulled the 150 FMJ's, put in a new powder charge and match bullets. The case head on one developed a pin hole brass flaw in the unsupported case head. Blew his magazine out and split the stock.

Brass flaws happen and there is nothing you can do to prevent them.

Due to the unpredictability of everything, always wear shooting glasses. My glasses have saved my eyeballs a number of times.

Zak Smith
June 21, 2010, 12:41 PM
I got a DVD in the mail with the SEM/EDXA images from 1858 over the weekend. I'll get something posted up here soon.

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