Author Topic: Gun Kaboom Incident  (Read 1232 times)

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Offline mauserand9mm

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Re: Gun Kaboom Incident
« Reply #15 on: May 27, 2019, 10:56:54 PM »
Squib makes no sense on a semi automatic, as the squib would not have cycled the slide.  So on a squib, there would have been a pause where he had to manually cycle the slide.

Edited: Wow, not 30 seconds after posting this I scrolled down and read another thread on squibs, where several posters mentioned that they HAD had squibs with enough pressure to cycle the slide.  ....

I really doubt that a squib would leave a bullet in the barrel and eject the case. Recoil operates the action, not pressure. The bullet moving forward causes the recoil. Besides, I never heard of this before. The only squibs that resulted in blown autos that I'd heard about were due to manually cycling a fresh round into the chamber after the squib.

Offline shootingsight

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Re: Gun Kaboom Incident
« Reply #16 on: May 28, 2019, 10:14:22 AM »
Recoil comes from the pressure, so it's really one and the same.  Chamber pressure simultaneously propels the bullet forward, but also acts on the base of the case, which in turn pushes on the breech face.  So it is that gas pressure that both propels the bullet and propels the slide back.

With a full load, the volume of combustion gasses increases as the bullet goes down the barrel, and eventually starts to vent once the bullet leaves.  With a squib, the volume does not increase, nor does the pressure vent.  So presumably a much smaller charge is able to action the slide.

Offline mauserand9mm

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Re: Gun Kaboom Incident
« Reply #17 on: May 28, 2019, 06:08:02 PM »
Yeah you are right. There are two components to it however - gas pressure and conservation of momentum (ie recoil). I tried to do some math/physics to see how much each effect has but got stumped. I'll get back on to it when I research some more (have a keen interest in it now). My gut feeling was that recoil was the largest component - could be wrong.

What makes me find it hard to accept that a squib can cycle the action is:
- when I worked up loads in my 9mm, the loads that were too light still fired with reaonable velocity but failed to cycle the action completely, so how can one cycle completely where the bullet failed to reach enough velocity to exit the barrel? (but I guess the presssure is kept captive for longer allowing it time to act and cycle the action?)
- I've had loads as low as 280ft/sec still exit the barrel.

But maybe squibs still had high pressure? - this contradicts being able to expel the projectile out of the barrel though. Maybe squib projectiles were too large - but then how did they manage to be chambered?

Offline shootingsight

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Re: Gun Kaboom Incident
« Reply #18 on: May 29, 2019, 09:13:13 AM »
Sorry I was not more clear.  There is no such thing as 'recoil' which acts independent of the pressure.  The force we call 'recoil' is 100% the pressure of the gas acting against the breech.  It just so happens that the force of the gas against the breech exactly equals the force against the bullet.  F=m*a, so the force of the gas against the bullet is the mass of the bullet * the acceleration of the bullet.  F is also equal to the mass of the gun * the acceleration of the gun (sort of, the math gets messier when you consider the slide moving relative to the frame, but never mind that for now).

So you have gas pressure acting against the gun in one direction, and gas pressure acting against the bullet in the other in an equal but opposite manner, causing acceleration of both.  We call the acceleration of the gun 'recoil'.  Since we established that F for both is equal, the acceleration of each is in proportion to the mass of each.  ie if your bullet had the same weight as the gun, you would accelerate both equally.

The question is then: how much pressure, and how much mass.  In a regular firing, a lot more gas is produced, so it drives the bullet down the barrel.  The balance is therefore mass of gun vs mass of bullet, though the volume of gas incresases as the bullet goes down the barrel, and eventually vents as the bullet leaves the muzzle.  In a squibb, the gas volume is a lot lower, but there are two things that are different: first is that the bullet lodges in the barrel, so effectively the momentum equation has the mass of the slide going one way, and the mass of the bullet + barrel + frame going the other.  So the slide gets accelerated one way, and the frame the other.  Additionally, the gas is trapped and does not vent until the case unseals the chamber, so the impulse lasts a lot longer.

I've never tried running the math in detail, but take from these other posts saying it happened to mean that the math would work if you had the right weights behind the frame and slide, and your primer were powerful enough.

Now you have me thinking if I want to go and intentionally load squibs for different guns, to try this out ....

Offline zhuk

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Re: Gun Kaboom Incident
« Reply #19 on: May 29, 2019, 12:19:42 PM »
Guy at my club once double-loaded Bullseye in his M&P, he was chrono'ing at the time how we found out it was 178PF lol

(that and the *BOOM!* was a bit of a giveaway)

Gun was fine afterwards...had it been an unsupported-chamber Glock, possibly not.

Offline mauserand9mm

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Re: Gun Kaboom Incident
« Reply #20 on: May 29, 2019, 10:56:56 PM »
Sorry I was not more clear.  There is no such thing as 'recoil' which acts independent of the pressure.  The force we call 'recoil' is 100% the pressure of the gas acting against the breech.  It just so happens that the force of the gas against the breech exactly equals the force against the bullet.  F=m*a, so the force of the gas against the bullet is the mass of the bullet * the acceleration of the bullet.  F is also equal to the mass of the gun * the acceleration of the gun (sort of, the math gets messier when you consider the slide moving relative to the frame, but never mind that for now).

So you have gas pressure acting against the gun in one direction, and gas pressure acting against the bullet in the other in an equal but opposite manner, causing acceleration of both.  We call the acceleration of the gun 'recoil'.  Since we established that F for both is equal, the acceleration of each is in proportion to the mass of each.  ie if your bullet had the same weight as the gun, you would accelerate both equally.

The question is then: how much pressure, and how much mass.  In a regular firing, a lot more gas is produced, so it drives the bullet down the barrel.  The balance is therefore mass of gun vs mass of bullet, though the volume of gas incresases as the bullet goes down the barrel, and eventually vents as the bullet leaves the muzzle.  In a squibb, the gas volume is a lot lower, but there are two things that are different: first is that the bullet lodges in the barrel, so effectively the momentum equation has the mass of the slide going one way, and the mass of the bullet + barrel + frame going the other.  So the slide gets accelerated one way, and the frame the other.  Additionally, the gas is trapped and does not vent until the case unseals the chamber, so the impulse lasts a lot longer.

I've never tried running the math in detail, but take from these other posts saying it happened to mean that the math would work if you had the right weights behind the frame and slide, and your primer were powerful enough.

Now you have me thinking if I want to go and intentionally load squibs for different guns, to try this out ....

Still trying to wrap my head around it. Newton's 3rd law - for every action, there is an equal and opposite reaction. I think you'd find that if you took two otherwise duplicate loads with the same pressure and for the same duration, one with a projectile and one without (ie sealed barrel), the recoil would be different between the two. If the barrel where plugged the pressure would push it forward as the slide went back, and the pistol may have zero net "recoil" but would probably move about abit- still the same force in both cases. The mass that the force is acting on has an effect, or rather what it is doing. So the projectile does contribute to the net recoil but I'm not sure if this also increases anything to the slide movement.

I'd like to experiment with squibs too now, but I know I would be frowned upon at the range. I wouldn't be keen on knocking out stuck projectiles either (fear of damage to the rifling - I'd use a 22 case over a steel rod to knock the bullet out BTW. Wooden dowl can split and get stuck.)
« Last Edit: May 29, 2019, 11:04:39 PM by mauserand9mm »

Offline noylj

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Re: Gun Kaboom Incident
« Reply #21 on: May 30, 2019, 02:37:11 AM »
Just my two cents:
Why do they allow over-SAAMI pressure rounds in competition anyway?
There may be some powder in combination with some bullet weight/profile that can meet major without exceeding SAAMi pressure, but I haven't seen it.
Thank Luger for making a strong case for folks to play with.

Offline noylj

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Re: Gun Kaboom Incident
« Reply #22 on: May 30, 2019, 02:41:19 AM »
In a closed system, you have a balance of forces, like a balloon. While a closed system, there is no real action or reaction. The bullet will be pushed down the barrel and there may be some small push back during the microseconds of bullet travel, but pressure is still balanced in all directions. However, once the bullet leaves the barrel, you have an open system and recoil equal and opposite to that of the bullet (the barrel at that point is like a small rocket being propelled back due to escaping bullet and gas).

Offline mauserand9mm

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Re: Gun Kaboom Incident
« Reply #23 on: May 30, 2019, 07:52:20 PM »
Yeah but even if the projectile never left the barrel, the pressure would force the slide back, and the reaction to the slide moving backwards is the rest of the pistol being pushed forward - I think "net" recoil would be zero because no mass is leaving the closed system. I think you only get "net" recoil is because the forward moving mass (projectile and powder) is leaving the system, as you've said.

So does that mean that only the pressure cycles the action, and the only effect from the projectile leaving the barrel is "net" recoil of the pistol ie without any effect on the cycling of the slide? Actually I think that's it.

So the question is how come the pressure can operate the slide and not eject the projectile? I've loaded loads that ejected the projectile but didn't completely cycle the action. If I kept reducing the load the pressure would drop and the projectile would leave at a lower velocity, until eventually the projectile would not the barrel. Even though the pressure is reduced at this point, it still has to go somewhere - cycle the action? Most squibs I heard about, or have witnessesed, were due to no powder. The primer has enough power to jam the projectile in the barrel but not eject the case. Don't know if it manages to move the slide at all. (Probably doesn't allow the case to expand properly and seal the chamber, so leaks out quickly after the projectile leaves the case.)
« Last Edit: May 30, 2019, 08:12:36 PM by mauserand9mm »

Offline shootingsight

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Re: Gun Kaboom Incident
« Reply #24 on: May 31, 2019, 09:11:13 AM »
You get the same pressure acting in both directions, and Newton's law says that momentum is conserved, so the momentum (mass x velocity) of the bullet + gas will equal the momentum of the gun, except that the sign will be opposite, because velocity is in the other direction.

So 'recoil' is based on the mass ratio of the gun versus the bullet.  Shooting a heavier bullet will increase recoil, shooting a lighter gun will also increase recoil.

Pressure x area is force, so 50,000 PSI x 0.01 Square Inches (9mm base), means 500 lb of force acting on the bullet.  F=ma, so 500lb divided by 115 grains (plus powder load) will give you an acceleration.  Acceleration x time will give you a speed, so multiply the acceleration by barrel time and you get a muzzle velocity.  Obviously it is never as easy as that, because you lose some force due to friction, the chamber pressure is not constant, bla bla bla, but the concept gets you started.  That SAME 500lb force is acting on the gun, for the same amount of time, but say a gun weighs 2lb (14,000 grains) instead of 140 grains (bullet plus powder), so if the bullet achieves 1,000 fps, the gun will achieve 10 fps.... or at least a revolver will.  A semi gets messy, because some of the energy is used to compress the slide spring.

A squib only needs enough energy to compress the slide spring.  bleep it, now I'm thinking I need to take apart a gun and measure the slide spring to calculate how much energy.  I need another project like I need a hole in the head, but bottom line is that despite being messy, you can probably get within 20%, despite the simplification of the math.

Offline Fuzzy Sights

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Re: Gun Kaboom Incident
« Reply #25 on: June 01, 2019, 01:02:14 PM »
A lot of local shooters shoot Major 9 and use range brass.  There have been a couple of incidents where loads safe in most 9mm brass was not safe in heavier and thicker brass (S&B, etc.).  Fortunately only one has resulted in damage to the firearm (a Glock).  Personally I am paranoid and shoot only one headstamp in 9mm when developing a load (Speer or Win).

JW