Alternative Measure Pressure?

jski said:
Woe, woe, woe, are you saying that every time you fire a round in a revolver, the case slams up against the recoil plate/shield? That the lateral pressure against the chamber wall prevents nothing? I want to be very clear here.
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That is correct the thrust back against the recoil shield (often called bolt thrust) of a revolver is directly proportional to both the chamber pressure and diameter of the chamber. A first order approximation is the pressure times the cross sectional area of the chamber. If you really model it correctly their is a small amount of resistance from the friction of the brass against the chamber walls but that resulting force is really small. In addition the brass itself is not strong enough to support the pressure/force without the recoil shield there to support the brass. Think of it as the brass acts as a gas seal the steel of the revolver contains the pressure.
 
The link above discusses rimless rifle cases fired from a boltgun where the bolt stops the case + lateral pressure against the chamber
 
Let me ask another question: if the cases in a revolver are slamming up against the recoil plate wouldn’t/couldn’t I see that in a full moon clip in a 45 ACP wheelgun?
 
jski said:
Are there videos of this?
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Given the speed of that event and the really tight space through which you could see it happening it would take a very deliberate effort to video that with very expensive equipment. I would not be surprise if it has been done but I can't find any videos.

You can sort of prove it to yourself. Take a freshly sized and primed case and put it in your revolver and fire it. In many cases you will find the primer partial backed out of the case. Do this safely if you do and remember it may be difficult to open.

ETA: as minor tangent this is why if you see the quick draw shooters that are shooting wax bullets propelled only by the primer they often drill the flash hole out larger to reduce some of the back pressure created by the restriction of the flash hole. Keeps their revolvers from locking up.
 
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The whole issue with reading case head expansion is that it is highly dependent upon case support which is a factor of the dimensions of the chamber. Unless a gun is a higher end gun the chamber was probably cut with a tool used on hundreds if not thousands of chambers, and it’s a wear item. Sometimes wear items take damage earlier in their wear life than they should and if that damaged tool still produces a passable chamber then it keeps running. There are tolerances for chambers just like there are tolerances for everything else including excess head space. So with so much working in different ways around the case head you just don’t know what a case is gonna do until you have done it a bunch and get a feel for THAT chamber. All that same bunch of variables also applies to the manufacture of brass. How big is that flash hole for the primer again? Add varying brands and loads of ammo and variables increase significantly. 9mm… is it normal brass or stepped brass? 45acp small or large primer? 5.56 crimped or not? What heat treat? Military or commercial?

Sure it’s a good thing to watch and understand when your pushing pressure high up near (or over) max load, BUT it’s highly dependent on so many factors that there’s really no science to it. It’s about like watching primers and “reading” them for pressure. Great practice, but not the end-all be-all of pressure guesstimating.
 
Guys, this is quite the education and I greatly appreciate it. I would say very few people, even experienced shooters, understand this.
 
mcb said:
You can sort of prove it to yourself. Take a freshly sized and primed case and put it in your revolver and fire it. In most case you will find the primer partial backed out of the case. Do this safely if you do and remember it may be difficult to open.
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Yep, I did sort of prove it to myself when I conducted that test (mentioned in post #16) many years ago to try to determine if oil, (or water, or WD-40) would deactivate primers. I primed a half-dozen cases, then put gun oil in a couple of them, water in a couple more, and WD-40 in the other two. The next day, I dumped the liquids out of the cases, put the cases in my revolver (a .357 Blackhawk if I remember right) and fired them - after having to stop several times and remove my revolver's cylinder because the darned primers backed out of the cases, which stopped the revolver's cylinder from turning. :oops:
BTW, CCI primers were only about a penny apiece back then, and they all went off. Although, a couple of them did sound kind of "weak.":)
 
I always just assumed the case may move back slightly but certainly not slam into the recoil plate with the primers being reseated after being punched out of the case. That’s extraordinary.
 
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jski said:
I always just assumed the case may move back slightly but certainly not slam into the recoil plate with the primers being reseated after being punch out of the case. That’s extraordinary.
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A whole lot happens in that millisecond. And now that you understand more, you can start looking at more stuff when considering a new gun purchase. I look at a few firing pin cuts and how much excess space is there because I know I’m going to push most things that I load for, and I’m not shooting it if I’m not loading for it. Glock has one of the worst oversized and oddly shaped firing pin cuts I have ever seen consistently with any brand. They also have less chamber support than many brands. There’s only 1 Glock in this house and it’s my wife’s 42, that’s probably not gonna change.
 
Don't worry, eventually something based on real science or contemporary tech will come in from New Zealand or Canada to address actual pressure measurements :rofl:
 
jski said:
Woe, woe, woe, are you saying that every time you fire a round in a revolver, the case slams up against the recoil plate/shield?
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"For every action, there is an opposite but equal reaction." Sir Isaac Newton (aka Newton's Third Law)

If the bullet is going forward (down the barrel), then the case is going backward (toward the breech face) with the exact same force. This because the gas in the chamber is pushing equally on both. It's been this way since 1679.

Mr. Newton beat Samuel Colt by ~190 years, so Mr. Colt was forced to include this as an "added extra". And it's been in every handgun ever since. ;)
 
rfwobbly said:
"For every action, there is an opposite but equal reaction." Sir Isaac Newton (aka Newton's Third Law)

If the bullet is going forward (down the barrel), then the case is going backward (toward the breech face) with the exact same force. This because the gas in the chamber is pushing equally on both. It's been this way since 1679.

Mr. Newton beat Samuel Colt erby ~190 years, so Mr. Colt was forced to include this as an "added extra". And it's been in every handgun ever since. ;)
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Admittedly my assumption (never really questioned it) that the lateral pressure on the case wall against the chamber would prevent the backward motion of the case was wrong. But even if that had been true, Newton’s 3rd Law would have come into play.
 
Recoil is the opposite reaction you speak of, thrust on the breech face from propelling the projectile.
 
In revolvers the hammer hitting the case moves it forward, pressure pushes the case back to the stop, and then the pressure pushes the cylinder against the forcing cone to create the seal. Your revolver should get a brass head impression on the stop and at the same time there should be a circle formed at the front. The brass is a gas seal and just something to hold the ammo together until it gets fired (unless it's a level 1 45 colt then forget the tight brass seal).

To much headspace makes the primers flatten as the case gets a running start. The same load in a carbine may show very little primer flattening. An unsquarly cut forcing cone can cause gas escape or flex the frame and or cly pin causing shots to not fall in tight patterns.

The sloppier the cyl gap on both ends the more and inconsistaint the flex will be. You have to have some at the head end to accomendate different brass makes and some at the cone so the cyl will turn when hot or cold and with a little crud built up on it.

Just an observation that can be seen on about any revolver. This one has about .007 clearance but still closes the gap but it's not the most accurate firearm in the rack. It flattens primers more than it should also. Loads are loaded to starting or lower charges in most cases but it is a magnum and shoots point of aim with the right loads.

IMG_20231009_185609046~2.jpg
 
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The concept of equal and opposite reaction is being misapplied here.

The correct idea is that when you pull on a rope, the rope equally pulls back on you, i.e., a force "couple".

This does not mean that the bullet and the rear of the cartridge case experience equal force. Take for example the 223. If gas pressure is the same throughout the case, the rear of the case experiences much more force than the bullet, because force is pressure times area, and the rear of the case has much more area than the base of the bullet.

Recoil is most easily modeled with momentum. Momentum is conserved, where force is not.
 
I’d love to see a high speed video of these dynamics in action. That would be an education for many! Of course, including myself.
 
I do have one question tho: If it is the case slamming into the recoil plate in a revolver the reseats a partially ejected primer, what reseats a 45 ACP partially ejected primer fired from a 1911?
 
jski said:
I always just assumed the case may move back slightly but certainly not slam into the recoil plate with the primers being reseated after being punched out of the case. That’s extraordinary.
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Good reading but there is a reason for strong bolts, slides
 
fxvr5 said:
The equivalent; the slide's breech face.
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Also remember in most other actions other than revolvers there is little to no gap between the breach face and case head. Revolvers require that clearance to allow the cylinder to rotate. A semi auto can close tight on the case, and most do, pinching the case between the case head at the beachface and case mouth in the chamber (or the front of rim in the case of a rimmed cartridge) so the primer has much less room to move.
 
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jski said:
Are there videos of this?
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Videos I am not sure about but I can provide a few images as they apply to rifle cases. Below are some 7mm-08 Remington cases I primed and fired in a 7-08 bolt gun. The cases were simply primed, no powder and no projectile means no real pressure to speak of. No cartridge head slamming into a bolt face, just a boring pop. :)

7mm-08 Savage Axis.png

Since there was not adequate pressure to violently slam the cartridge head into the breech face the primers are not flattened.

Primers Flat 308.png

Flat primers as a result of slamming back against the breech face.

Edit: The off center look of the second image is a result of poor camera angle. :)

Ron
 
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