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Discussion in 'The 10 Ring' started by deadandgone, Feb 2, 2013.
Excellent post, Shadow, as usual.
Your post is ok, but this part...
is totally wrong. Nothing is dragging the cartridge out under pressure, and it cannot push itself out. There is something like 5 tons of force needed to pull the case out of the chamber during firing, and less than 1 available to push it to the rear.
The things that caused a problem was a manufacturer ignorant of simple physics creating cartridges that were far over safe limits, and loading them uing a faulty process with non-existent quality control.
I agree that they these cartridges were over loaded...Yes at the peak of pressure the casing stretches to fit the chamber...but
Once the case has started to tear due to excessive forces, and as it stretches to fill voids, the moving metal can work to force itself further out of the chamber like a pry bar or lever. This can be seen by placing cartridges back in the chamber for measuring purposes, in this insident we don't have the brass to see. Some smiled brass have shown more stretch than the original support of the fully chambered round. The blow back action is dynamic and extreme forces change those dynamics...but think about the entire event, not just the highest pressure peak phase. Even as pressure is dropping off some work can still be done before the complete drop off.
Another part of the equation is the emense amount of heat produced, this changes the properties of the brass as it absorbs this energy, the chamber walls act to absorb some of the heat from the brass, but the unsupported areas don't have that advantage. The amount of heat sink is not there, so it is subject to the high heat stress in addition to the high pressure. This combination is probably why we see the blown out brass at the feed ramp area...
I do ask myself what if different brass was used? Would this have still happened?
The point of saami specs is to keep questions like that from arising. If you are working in the limits there won't be a problem. The gun, brass, primers, etc. will handle it. If you run outside the specs you are just guessing as to which part will break first.
With hot rod cars you beef up each part that breaks, and over time the entire system becomes stronger. With reloading, you should be adhering to a spec to insure that parts do not break, as results can be catastrophic.
I still don't see the possibility of the early unlock you worry about, but will concede that I was almost wrong once, as evidenced earlier in this thread...
Sorry Any Cal. Shadow is right in his thinking.
Many auto pistols unlock early. Is it enough to cause a kaboom? No. And one does not need over spec ammo to see it. Every time I go to my range I can always find brass thats been shot from a semi auto pistol that has unlocked a tad early.
Because Glock doesn't make a .41 Magnum. I Can't find a 1911 in .41 Magnum either.
You know this is just not a Glock problem! Here is a story of a S&W Shield KB using Cor Bon Glaser Ammo.
Shadow, the highest recoil spring is 24lbs for G20 and 23lbs for G29. Are they the best remedy for early release ? I think of the problem as expansion outside of the chamber, so if we keep it in chamber longer then it'd be ok.
I wonder what we CAN do, if it is inherent to the design of some hand guns.
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I think those if us who handload hot realize there is too much varianceIn those charge levels. Swampfox made some serious ammo, but...
We can all speculate some here, based on everyone's experiences, however I am not trying to flame anyone and I do read everyone's expressed views and take them in as part of my study...as a reminder this is 40S&W SwampFox Ammo loaded HOT (too hot) in an aftermarket barrel on a Glock 29, extra power RSA and some other things.
Things that do also come to mind...
Read at CCR raceframes...http://www.ccfraceframes.com/faq-barrels.html
Locking blocks, back a while Carrier had his break. While he was testing some hot loads, did the barrel (aftermarket IIRC) have angles of the lock lug different that led to the locing block breaking? Not known...
Deadandgone started experiencing some issues prior to the KB, did the locking block fail? Did that lead to out-of-battery situation? Early Unlock? Don't know...
Went to find brass in the woods where the explosion occurred. When I say woods, a heavily wooded area near my home. Took the wife with me, and we both searched for the casings...unable to find anything. No metal detector, just two sets of eyes...no luck.
Shadow, the instances of "unusual bullet behavior" occured with my xdm 40 cal. Prior to the explosion in the g29, there were no tip offs or clues as to what was about to happen as I was shooting the Glock. Again, a really bad misconception on my part...I knew the ammo was behaving oddly, but I felt safe shooting it in my g29 allmighty. It is simply luck that it didn't blow up the xdm.
I don't want to speculate what would have happened if the xdm had blown up. I am just glad that Glock makes a sturdy gun...and that the main force of the kaboom seemed to go down as opposed to backwards.
I have no brass to back up my thinking....I wish I did, it would tend to solve the mystery part of the explosion. However, given the measurements provided by Shadow, I feel confident that the ammo failed, was too hot, and created the explosion. Had I not been so naive in my thinking, this thread would not exist, so I cannot eliminate my part of this equation.
We can substitute the word ignorant for naive...both words fit just fine. I didn't know any better....my thinking was flawed.
Now, I know. If I were to load ammo that crossed the line between safety and hot ammo....I'd be in business selling Swamp Fox ammo.
Sorry, it kind of hurt to say that, and I will never sell any of my remaining stash of 10 mm Swamp Fox ammo. I won't shoot it, but I won't sell it. Especially the stuff marked "supported barrel only".I know the difference between right and wrong...the line is not blurry for me. And Mike, if you were still alive, I would tell you that....face to face.
And, as Forrest Gump might say, "And thats all I have to say about that."
Shadow, I think that is absolutely a possibility. I would think that a locking block would break while the barrel was smacking it traveling back towards the shooter in recoil. If that is the case, then the broken locking block would allow the barrel+slide to remain locked longer than necessary. This would cause the normal locked dwell time to increase, not decrease, so that would actually make a KB less likely on that round. On the next round, if it chambered for firing, the barrel+slide might not be fully locked in the normal forward position, reducing the travel of the locked slide+barrel. For a typical handloaded hot 180 XTP at 1200fps, if the normal unlocking travel were reduced from .210" to .070", that would most definitely cause a KB! See explanation below....
Physics: It's not just a good idea, it's the law!
OK, I've been wanting to do this for some time now, but never sat down and took the time to do it. But what I've done is to create a spreadsheet to do some calculations on barrel-slide lock time, pressure, slide velocity, etc. Based on a realistic velocity for firing a 180XTP from a G29, and some assumptions that I've made below, I've checked my numbers a couple of different ways, and I'm 99% sure they're OK. It took a while to figure out how to work the math using the English (pounds, feet, etc.) system. The SI system (MKS) is so much simpler!
- Glock 29
- Barrel weight (weighed) 4.0 Oz. (0.25lb)
- Slide weight (weighed) 15.6 Oz. (0.975lb)
- Slide + barrel (locked) 19.6 oz. (1.225 lbs)
- 180gr. XTP fired at 1200fps plus 10gr. of powder(hot, don't try this without working up)
- Slide travel before barrel unlocks from slide (measured) 0.210"
- Spring force 17lbs
- Linear acceleration ***
- Distance bullet traverses barrel 3.145" (measured from where a 180 XTP would be positioned in the 3.77" barrel in chamber when shot is fired)
- Conservation of momentum, M1*V1 = M2*V2, where "1" is bullet and "2" is barrel + slide
- Neglecting slide friction and small amount of momentum transferred to the shooter in the first 500 us of shot initiation (time it takes to get the bullet out the bore).
- Neglecting force of "jet effect" of combustion gasses leaving the barrel after the bullet has cleared the muzzle.
*** The assumption of linear acceleration here is totally bogus, but it does fit within the use of the conservation of momentum equation. The problem with figuring actual time-based acceleration is having a precise pressure curve, then knowing what the force of barrel friction + bullet obturation is. This is still going to require some assumptions, because you can't precisely measure the time vs. pressure curve with load cells. A properly calibrated piezo could (could meaning "properly calibrated" and applied) get you very close. However, we can precisely determine what the velocity of the bullet is when it leaves the barrel, so that is what the spreadsheet is based on. The best method, IMO, would be to attach an accelerometer to the slide. Then you would know exactly how the slide velocity changes as the bullet traverses the barrel.
So what I did in my spreadsheet is to calculate, based on linear acceleration (assumption is a constant force is applied the bullet and powder mass to move them down the barrel). The counter-force to this acceleration must be an equal and opposite force applied by the system of the locked barrel-slide combo and the recoil spring. The resulting force in both directions turns out to be appx. 2320 lbs., and the bullet would leave the barrel appx. 437 microseconds after this force was applied.
In order for unlock to occur while gas pressure was still in the barrel (i.e., bullet has not left the barrel), the slide-barrel combo would have to travel the 0.210" backwards into the unlock point (locking block) faster than the bullet can traverse the barrel. Applying 2303 lbs of force to the 1.225 lb mass of the barrel + slide, the time it would take to reach the unlock point under 2303 lbs of force (subtracting the 17lb spring force) would be 761 microseconds. If I assume that the opposing forces are terminated as the bullet leaves the barrel at 437 us (neglecting gas jet effect), then my numbers for momentum are exactly balanced.
Here's some interesting observations from this exercise:
- Calculated slide velocity is 26.4 fps
- Changing the spring from 17lbs to 22lbs only changes slide velocity by 0.06 fps. (note that a 22lb spring will decelerate the slide motion much more quickly than a 17lb spring, that's really the only benefit to extra spring force)
- Reducing the slide mass by one ounce increases the slide velocity by 1.42 fps.
- Increasing spring force is not going to significantly delay unlock time. Completely removing the spring in this system makes almost zero difference in unlock time. No spring at all would not cause a KB.
- Mass is critical to control slide velocity, but it takes a huge reduction in slide mass for unlock to occur early. The normal barrel + mass of 19.6 Oz, all other factors held the same, would have to be reduced to appx. 6.5 Oz for KB to occur (assuming this "normal ammo" pressure)
- Slide travel to unlock is critical. In this case, all other things held equal, KB would occur if the distance was shortened from 0.210 to about 0.070" (could the KB round have fired somewhat out of battery/incomplete lock-up?)
I tried all kinds of practical changes to the system to induce an unlock condition, and I couldnt, even at 100,000 psi. Of course, I did make some assumptions on pressure-time curve, and neglected the "jet-effect" of gasses continuing to exert force on the barrel-slide combo.
So, I'm not claiming to be a gun expert, and I certainly could have made errors in my assumptions, especially with the linear acceleration, but it seems to me that the system is designed to never unlock under practical conditions, regardless of the chamber pressure.
OK, flame proof suit is on, fire away!
TDC20, I can't argue with the laws of physics. Your numbers do make some sense with regards to the dynamics involved. We are beating this thing to a pulp as we all scratch or heads for answers...
The slide and barrelremaining locked during the entire pressure event should not cause a blowoutunless, gross lack of case support and the overcoming of the strength of thematerials (brass)...or both.
If something moves to increase the unsupported areas, thenmore catastrophic failure is certain.
I think about proof testing which is required by SAAMI, they test beyond thestandard operating pressures for this test...for the 40S&W & 10mmcartridges their proof pressures would be within 130% minimum and 140% maximumof the MPLM (Maximum Portable Lot Mean)
10mm Service Maximum Average Pressure = 37,500psi
40S&W Service Maximum Average Pressure = 35,000psi
Pressures Values of Proof Cartridges
10mm Minimum average = 50,500psi 10mm Maximum average = 54,000psi max e.v. =98
40S&W Minimum average = 47,000psi 40S&W Maximum average = 50,500psimax e.v. = 92
Data from SAMMI publication 205 http://www.saami.org/specifications_and_information/publications/download/205.pdf
Where these cartridges as loaded, within even these limits or did theysurpass even these pressures? We know from the retrieved load data that theywere over recommended data.
Hodgdon shows simular 165gr bullet with 7.8 grains @ 1185 fps with a pressure of 33,400 psi.
We know case support is always a factor to allow forces to overcome thatsection that is the thinest or weakest...
Will the Brass fail at or above these kind of pressures? At what pressuredoes the Brass fail?
I think that's the question that needs to be answered. Based on my exercise, it looks like there are only 2 plausible paths to the KB. One is where the brass fails under excessive pressure, bursts at the weakest, unsupported point, and blasts hot gasses down towards the mag well. The other would be due to a breakage or other defect causing the locked barrel and slide to be positioned considerably short of the normal starting point when the shot is fired, which then causes unlock before the bullet leaves the barrel and the gas pressure falls.
I got to thinking, the best way to test brass failure would be to use the hydraulic method, similar to how they test scuba and gas tanks, called a hydrostatic pressure test. I'm sure you're familiar with this, Shadow. The idea is that water, which is relatively incompressible, is forced to extremely high pressure using a hydraulic action. If the system fails, there is no great explosion or anything exciting like that, the water just runs out. I think if I remember right, Scuba tanks need to be hydrostat'd every 5 years. I think that is true of all high pressure gas tanks.
Anyway, if a test could be performed on a piece of empty brass while positioned in the chamber of a test barrel, we could theoretically answer that question. I don't have access to that type of test equipment, though. Maybe a university materials research lab could do it. The government may have already done it.
This never occurred to me before about after market barrels. I'm going to take a closer look at mine and try to determine if they provide the same amount of travel to the unlocking point, and inspect for damage.
The equations for the timing are very interesting. It shows that, as pressure increases and bullet velocity increases, there is still significant margin in the timing in that the bullet leaves the barrel before unlock occurs. I simulated a 3000fps+ 180gr bullet from a G29, and there was still over 100 microseconds of margin! What happens is that the slide acceleration increases significantly under those conditions, but the bullet is traveling so much faster down the barrel that it still clears the muzzle before unlock. I've concluded that for a fully supported barrel, the barrel may actually burst from overpressure before a KB occurs from unlock, unless some other factor significantly reduces the slide travel distance to the unlock point.
I think I saw an AM barrel that did just that somewhere on GT within the past few weeks. It was a fast burning powder that could have been double charged, and I think it was a .45. Of course, there could have also been a stuck squib bullet in the barrel when the exploding shot was fired, too. Still, excessive pressure is excessive pressure. The barrel fragged from the breech end.
I think "we" routinely run handloads over the SAAMI pressure limits in the 10mm. I can't prove this, of course, but I'll continue to believe that brass that is heavily glock smiled was run well over the intended pressure limits, and dangerously close to KB'ing. The fully supported barrels just allow us to "get away with it" for a while. If the Glock barrels can handle proof loads in the 50kpsi range, then I imagine some hand loads I've read about here are well in excess of that. A lot of folks used to pooh-pooh the results of Quickload software in predicting pressure for some popularly accepted loads. Maybe Quickload is closer to the truth than we wish to admit?
1911 Tuner always said that a recoil spring made no difference in the recoil operated system of a 1911 and by extension, a Glock. I have been waiting a very long time for someone who knows the formulas to run out the problem.
I don't have any reason to flame you, similar specs have been mentioned by other people in other times. Having some kind of numbers specific to a Glock does help to make ideas that were somewhat unbounded considerably more concrete.
Any Cal, I think what TDC20 is sayin is that:
(1) "Changing the spring from 17lbs to 22lbs only changes slide velocity by 0.06 fps" during the first 0.210-inches of slide travel, but
(2) "a 22lb spring will decelerate the slide motion much more quickly than a 17lb spring" after that.
So, the strength of the recoil spring makes a big difference in the process, but just not in the first 1/5th of an inch in rearward travel of the slide.
Remember that the spring's force = 0.5 * k * square(distance) plus mfg rated force.
So at zero distance, it is just 17 lbs or 23lbs, not much against the explosion. But as distance increases, force goes up by half of the distance squared. That goes up by the law of exponential squared. for practical purpose of early unlock, assumption of mfg rating and linear behavior is close enough.
Now, turn to the issue of "nearly" in battery, a strong spring would regenerate enough velocity and force from recoil, to slam it into full battery a little more authoritatively. Right?
Causes for short of full battery that I've seen are:
- Too long OAL.
- dirty gun, too much friction or impeding of slide action (case sliding into extractor not smooth)
- primer not fully seated.
I'm sure there's more, like improper dimension barrels. But in my experience, all of my current 10mm barrels, KKM and SLake, impart no dent on the frames. I did sell another mfgr's barrel because it wasn't reliable in slide action.
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I applaud the sensible application of physics that has been used here. It's been a few years since my last physics class, but from what I can remember the math looks sound. We have to remember (and TDC20 recognized this himself) that we are making a lot of assumptions when trying to deal with this problem.
That said, how do we explain the extreme velocity spread that many have reported when shooting high powered ammo with the stock spring that is significantly reduced when switching to an aftermarket 22+ pound spring?
If it is true that running an aftermarket spring greatly reduces velocity spreads when shooting high powered ammo, then we could reasonably infer that the barrel is staying locked up for a longer period of time before unlocking.
That would then lead us to ask how this could happen, in spite of the mathematical evidence we have been shown to the contrary? I would postulate that either: (1) there are significant variables that we are not accounting for; or (2) there are variables that have not been correctly represented.
A big problem that I can see is that while we're talking about a 17lb stock spring vs. 22+ lb. aftermarket spring we do not know all of the important specifications of these springs. Are these the true spring weights? Are there overall length differences between these springs? What is the actual amount of force being placed on the slide while at rest (pre-load)?
I don't have an answer these questions, but I do think that in light of some evidence we have that contradicts our current mathematical findings maybe we need to take a deeper look before concluding that different springs do not significantly alter lockup time/characteristics.
I should have been a bit more clear. I wasn't saying that a recoil spring didn't do ANYTHING, but that it didn't do anything significant as far as increasing lockup. I realize that the extra poundage will do something at some point, and didn't mean to say otherwise.
The main point Tuner hammered on was that it was a slide return spring, and its main function was to return the slide to battery, and keep it in battery during normal usage. You will see this in the gamer's guns when they run too light a spring with a normal or heavy striker spring, and pulling the trigger pulls the gun out of battery.
I think the idea of velocity swings changing with recoil spring is a myth, regardless of the fact that the guy from Buffalo Bore really believes it. So far I have seen two cases where it should have shown itself, and it didn't do so in either case. What would be needed is someone who understood statistics AND internal ballistics to run some tests that would actually show something, rather than some nearly random guy claiming it works that way.