MtGun44: Not sure if you are referring to the missing recess in the same way as I am seeing it or not. It sounds like you are forgetting the bolt is rotated closed and the right locking lug is actually supported by the shoulder in front of the feed ramp and the left locking lug is supported at the top of the receiver ring. The pictures don't actually show these areas clearly enough to know what is left of the support areas.
Good point. One lug locks at the top (missing receiver portion here) and the
other at the bottom, hard to tell if the locking surface in the receiver is intact
or sheared, but it looks intact. I guess with the top one gone, the bolt could
move up and disengage the bottom lug.
Nasty mess.
Stick to proper pressure levels - 45K psi loads for the 7x57. Does seem to
make the FR7s a pretty marginal concept for running full power 7.62 NATO
ammo. I have some German ball that is pretty seriously hot stuff - steel
core and the primers are FLAT in HK91. It has the NATO cross and is accurate,
but it would be bad news for any rifle of marginal strength.
How about the proposition that FR7s were intended for the lower powered
aluminum core bullet loads that the early CETMEs were designed for and not
for full power 7.62 NATO? The chamber were the same, I think, and maybe
the Spanish assumed that since they controlled all the ammo, this was an
OK conversion because they were using low pressure loads.
Of course, once they are sold surplus, you will find folks stuffing whatever
they can get to fit into the chamber.
Kaboom.
Bill
If it was easy, anybody could do it.
Hello BillOriginally Posted by MtGun44
I read both your notes on the two rifles.
I like the way you walk down the road and describe what you see on the way without feeling the need to describe the color on the underside of butterfly wings. There are things that may be or may not be but you hit the important aspects succinctly and explain it without diarrheic verbosity. I appreciate that.
Dutch
Mtngun44
If we use the old 45,000 psi which is based on conversion from CUP then the current psi with modern pressure measuring equipment is 52,000 psi. The older pressure figure should be expressed as 45,000 C.U.P. One should also note that this is an American pressure figure used for the 7x57 cartridge and not one of German, Spanish or other European pressure level. Thus one must carefully detemine the relative meaning of "psi" not only with the 7x57 but with other cartridges as well.
"How about the proposition that FR7s were intended for the lower powered
aluminum core bullet loads that the early CETMEs were designed for and not
for full power 7.62 NATO? "
Not a correct proposition; if you can "hable espaniol" and read the Spanish manual for the FR7/FR8 you'll find they were fully intended to be used with 7.62 NATO ammunition and also could be used with the 7.62 CETME cartridge. Interesting to note that numerous lots of 7.62 NATO ammunition have not exceeded the 52,000 psi (3 different .308W rilfes) when measured by myself using a M42 Oehler PBL. Several lots of surplus 7x57 ammuntion excceed the psi of the 7.62 NATO ammunition. One lot in particular averaged over 60,000 psi!
Larry Gibson
What do you think the gold coloured dust is?
That's the vaporized case head. If that was a modern steel action that held together with kind of a case vaporisation, the action would have been brazed shut. I've tested rifles to this level of destruction on purpose. Your looking at over 100Ksi based my experiance. The problem with that statment is that pressure measurment at over about 75Ksi gets dambed near impossable to do it accuratly. The pressure pulse is too quick and too violent for the strain gages and signal processing to keep up with. But this statment is very accurate, that's not brass flow, that's vaporization.
Casting for .38 spec, .44 spec/mag, .45 Colt, 38-55, 45-70 and .50ML.... and the boy's slingshot.
Shake'n'bake powder coating is amazing. Thank you to the guys that developed and shared the process.
I believe the failure mechanism can be determined by a careful examination of the fracture surface. For all we know this could have been a fatigue failure. However, my question to all in this forum is could this type of failure be avoided if the metal has been heat treated? Although some distortion could happen during heat treating, so would it be more "prudent" to go to a case hardening treatment thus increasing tensile strength and wear resistance while still allowing the inner part of the metal to maintain its ductility and toughness. Does anyone have any experience with this? I have a company that quoted me $150.00 to nitride about 15 lbs of low carbon steel do a depth of .01 to .03 mm.
What do you think?
And to give a reference I have a 1916 Spanish mauser chambered in the 7mm mauser round that I am considering treating. And before you try to talk me out of this and convince me to just buy another rifle, I am considering this mainly because of the sentimental value of the gun ( it being passed on from my grandfather). And I dont want to just display it. I want to safely use it.
That failure had nothing to do with metallurgy. The high pressure gas did the damage.
Even a "vented" action can be blown up that way. When you feed high pressure gas into that large of an area, the forces are huge. Look at the damage to the bolt stop. That was all done by high pressure gas running down the left side rail - which is empty when the bolt is locked.
I have blown up plenty of weapons - and got paid to do it. I could probably duplicate that failure a couple of ways. A max load of 4895 & a fully annealed case might produce the same result. Shooting it with a cleaning rod still in it might do it too.
The picture below was from a testing program for a certain group of swimmers. We loaded the M16 under water, so that it was 100% full of water. Fired it under 4 feet of water. Spec. M855 round.
Now, that is as much bore obstruction as you can get. Pressures were very high. The gas blew the magazine catch clear out of the lower receiver, gutted the magazine (loaded with 19 rounds for the test) and slightly bulged the magazine well. The extractor was bent badly, and the action was a chore to open.
The bolt & barrel extension were in fine shape. Headspace checked ok. The upper was fitted to another lower, and that bolt/barrel/extension assembly were tested for another 5,000 rounds & magnafluxed. Still passed.
Guns can & do blow up. We should all remember that. OP, thanks for posting that picture.
B.
since this one is destroyed i would love to have the front sight assy. off of it for mine
The term metallurgy can mean the make up of the material and/or its heat treat or to a failure analysis determining the cause of the failure as swdepew is referring to. A failure can have only 2 causes, overload as you are referring to or fatigue which is caused by a latent defect and occures at loads below the design operating criteria. If the failure is fatigue, the failure could have occurred with any load. The fracture face tells the story.
Last edited by blastit37; 02-08-2011 at 03:38 PM.
US military specifications for the M-80 ball (NATO standard infantry rifle ball that typifies the ammo marked with the NATO interchability headstamp) cartridge is 48,000 CUP or 50,000 PSI EPVAT transducer. Maximum standard deviation is 53,000 CUP or 56,000 PSI.
The M118 Long Range cartridge on the other hand is rated at 52,000 CUP, with a 57,000 CUP standard max deviation of 57,000 CUP. These are not listed under PSI, only measured in Copper units of Pressure.
The Average working pressure of the M118 is 4,000 CUP higher than the average working pressure of the M-80 Ball, its Max Deviation is also 4,000 CUP higher or 9,000 CUP higher than the average working pressure of M80 ball which is around 20%.
The original proof test loads for the GEW88 and the SMLE and No.4 rifles (and possibly the 93 Mauser since it predates the increased proof test loads used for the model 98) were around the same pressure levels as an M118 cartridge that is on the high end of acceptable maximum deviation. Long range target loads for the .308 Winchester can have a average working pressure that exceeds the maximum deviation pressures of the M118 LRSB.
Most .308 hunting ammunition is no hotter than the M-80 ball, but theres no garantee that some or all the cartridges in any box won't push the maximum SAAMI limit of 62,000 PSI.
US Milspec proof test cartridges for the 7.62 NATO (HPT, High Pressure Test) are listed as 64,000-67,000 CUP.
The vast majority of documented failures of converted military rifles chambered for the NATO cartridge appear to have been due to defective ammunition from a single source.
Theres no available information on these since last I heard the company that made this ammunition or the Importer was neck deep in lawsuits and still trying to settle liability claims.
In that sort of litigation documented evidence may never be released to the public.
I have no problem with the older rifles so long as the action is not overstressed by the increasingly hotter loads being made available for the .308 and Long range sniper and MG loads in 7.62 NATO.
PS
In looking through Hatcher's research on low number springfield receiver failures I found one instance of a low number fracturing with pieces simply falling to the floor when a downloaded guard cartridge was fired. There was no sign of excessive pressure or an accidental doubled charge. His theory was that the faster burning 9.1 grain charge of Bullseye had reached peak pressure very suddenly giving the action a short sharp impact rather than the slower build up of pressure from a normal charge.
If so then many rifles that failed after firing very light loads of fast burning powder probably were not victims of accidental double charges as is often taken for granted.
No matter what the cause (and I have my own suspicions regarding the Spanish rifles) it's just one more reason to shoot nice comfortable cast loads........saves the gun and my shoulder!
I have 2 Spanish rifles I have shoot 7.62 nato rounds thru both but I mostly shoot reduced cast reloads. I also got 1 in 7mm never shot that one,no cases to reload yet. love all my mausers. some time people pick up wrong mil ammo that's not marked and blow up rifles. I never load max loads. but I am old man.
Don
Looking back at this post.
Please look very closely at the first picture. On the left side of the receiver ring, look at
the fracture surface, starting at the vent hole. It has two textures and colors there locally,
but the inner color/texture blends into the full depth of the metal as it reaches approximately
flush with the end of the barrel. The part over the top if the barrel looks possibly dirty and
slightly polished, which is a hallmark of a fatigue crack. This location looks to be at the end of
the barrel threads in the receiver - and a thread root is a stress concentrator. It is entirely possible
that the crack originated at the inner surface of the vent, traveled until it hit the bottom of the
thread and the followed the thread around to the other side. As with all fatigue failures,
the crack reduces the available material in the stress path until the remaining material cannot
support the load and it fails suddenly.
This is why there are two different surface textures in a fatigue failure - the crack is old and
corrodes and polishes against itself, but the final failure is bright, new and usually rougher.
I wish I could look at that fracture surface under about 10X magnification in really good light.
Bill
Last edited by MtGun44; 02-11-2011 at 03:06 PM.
If it was easy, anybody could do it.
I concur with MtGun44 and bohica2xo; this catastrophic failure was caused by an extreme overload of fast burning powder or a severe bore obsruction.
I might note, since this thread is referenced in the newer thread concerning a like occurence with a M96 action, that it was with a M96 in 6.5 Swede that SEE was first documented as fact and replicated some 25 years or so ago (I have posted the Handloader article on such on this forum). I will also note that very similar catastrophic failures of other actions (M70, M700s, Weatherby's, M14s, etc.) have been posted on this and other forums. The fault lies with the human operators and what they put in the rifles for ammuntion, not the actions. All are indicative of severe overloads with fast powders, bore obstructions or SEE (itself a self produced bore struction).
Larry Gibson
A good failure , but I have another idea about , FR8 and M96 cock on closing it mean when you close the bolt the firing spring compress , if some "smart" gunsmith touches the trigger sear to have a light pull the firing pin could be released before you turn the bolt to engage the receivers lugs , if the cartridges is ignited and the bolt not partial or fully closed , with 3/8 of the base of the cartridges outside the chamber all the pressure it's contained by the front ring , and it's not engineered to do it , it just explode ; this is why you see the bolt lugs intact and the lower reciever lug not shredded... the Spanish M93 have a guide on the left wall of the receiver , it's very difficult if it fail closed to open and retract 2 inches the bolt...
Just my idea
Daniel
Don't these have a firing pin retraction camming action?
Pin retraction is necessary to prevent pin wear or breakage during ejection cycle.
Its been many years since I've owned a 1895 but seems to me the firing pin could not contact the primer unless the bolt was fully locked.
An overly long firing pin, or a broken off firing pin tip jammed tight in its hole could ignite a primer on the forwards stroke of the bolt.
PS
Contary to what some believe, erosion and wear to the bore can create hazards and excessive pressure situations.
If the throat is badly eroded and the charge does not bump up the bullet enough to seal properly, blowbay can heat a bullet jacket to brazing temperatures before it travels past the eroded section. By then the bullet has lost much of its impetus and can be seized up in the bore while pressures are still building. This results in a pressure peak directly behind the bullet. If far enough up the bore a barrel failure will result before the pressure wave backs up to the chamber, if not far enough up then the casehead blows and action fails.
This can happen more easily with some light loads than with full house loads. A heavier charge being more likely to bump up the bullet and force it past the eroded section without seizing.
Other factors.
Excessive carbon and metal fouling infiltration of aligator checking in the leade. This reduces effective bore diameter swaging down the bullet slightly leaving windage to allow blowby.
Crazecracking. A real phenomena despite what some may believe. I've seen sections of lands cracked away in midbore by craze cracking.
Last edited by Multigunner; 02-11-2011 at 09:52 AM.
Sorry Daniel, but none of that applies here.
That bolt has been moved since the failure. After the smoke cleared, the bolt was probably still locked into the lower lug. Even if it had been blown clear out of the lower lug, it would not have rotated.
If the cartridge had been fired out of battery, ther receiver ring would still be intact, and the bolt stop would have mechanical damage - not gas damage. The extractor would probably still be on the bolt. I have done that test more than once, it is not particurlarly destructive.
The gas damage on that rifle is extensive. The proposition that the steel failed before the cartridge is bunk. The dark area at the top of the ring is a burn mark and likely the origin of the inital tear. Most people do not realize just how thin the ring is on a Mauser until they see one in this condition. The lower lug is far better supported than the upper.
The gas damage inches away (and past the charging cut!) to the bolt stop is very telling. That damage is consistient with other rifles I have examined that were blown up with high pressure events. The vaporized brass sprayed around the action is another clue.
Again, this failure had nothing to do with metallurgy. The same factors that blew this rifle apart would do the same thing in a M70 or M700 if duplicated. As to what the exact factors were - that will remain unanswered in this case.
As for a "gunsmith" causing this by "touching the sear" - nope. The original 2 stage trigger appears to be in the weapon, but cock on close or open the firing pin can not advance until the bolt is rotated. Even if you hold the trigger back it will not fire out of battery.
On rifles like the FR8, that have been stored in bulk & handled by many, there is a big concern over headspace. People swap bolts around all the time when there are hundreds of rifles laying around - and they do not know better. They were rebarreled at one time too. The only thing I would do with an FR8 before shooting it would be a headspace check.
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