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Smallbore has posted some time ago his experience of firing an unlocked Jones rotary underlever double with the lever open. In other words the gun was held closed by mere hand pressure. He did not notice anything untoward.

The forces acting on a double during and immediately after firing are a bit of a mystery. Even Autocad stress simulation does not adequately show the force development, it leaves out the friction component between shell case and chamber for instance, at least in the versions I saw.

How that piece came loose in the OP Smith seems, to me anyway, to be a result of pressure or corrosion than strain on the action from normal firing cycles.

Well I am certainly not buying that they are opening by Inertia as the movement is not in the right line for that. Until such time as I hear a better explanation I will stick with what I have stated. If someone has a better idea I'm all ears, but that is all I have come up with.

Assuming that there is enough force to cam open a system like the Smith, would that not create enough force for the barrels to continue their downward travel until the forend iron smashes against the underside of the action body?

If we fasten an action in a vice how much weight needs to be put on the barrels to cam open the action?

https://youtu.be/U_2gNhjAkjo

Note around 0.50 seconds the top lever moving right and returning. That would be interesting to analyse, is it due to parts inertia or camming? Fascinating stuff.

The video you posted is very interesting Shotgunlover, and if anything, I think it tends to verify Miller's theory of tapered bolting surfaces having a tendancy to be cammed open upon firing.

There would be a big difference in a sustained force of weight being applied to the barrels of a gun clamped in a vise, and the milliseconds impulse produced by the dynamics of firing. It would seem that the top lever spring returned the bolt and top lever back home within a fraction of a second in the video. One could imagine that it could actually pop clean open with enough camming force and a weak enough top lever spring to be momentarily overcome.

I have never experienced this in my own L.C. Smith's or my one and only Ithaca NID, but watching your video suggests that it is indeed possible. I can't recall the exact loads Buck Hamlin was using for his "Nuclear Loads" in his Damascus testing, but I am sure they were way above any normal sane proof load by the time the L.C. Smith in question was blowing open. It was even more impressive that he had lengthened the chambers in this ratty, rusty, pitted Damascus gun so he could stuff even more powder and shot into it. It would be cool to see an ultra slow motion video of those tests.

Yes as I recall Buck had opened the chambers to 3�" & was firing massive loads of Blue Dot with very heavy shot charges when the gun started opening. He had started with the heaviest loads listed for the 3�" magnum in the manuals & worked "UP" from there. I can't recall that I have ever heard of this being a problem with Smith guns using regular, even max, loads. It has been a problem with some NID's. As I recall it was a poor condition hammer gun with pitted barrels, yet he never "Blew" anything, just started opening it so quit at that point.
I do not know if he had the gun mounted un-movable for these tests or not. If not it may well have been the recoil motion being sharp enough that the "Barrel Dip" in recoil was putting enough force on the bolt to cam it around. Anyway you cut it thogh this gun was taking far heavier loads than it was designed to handle.

This was my Wifes grandfathers LC Smithgun on the Texas Prairie. How many times would the gun have been shot and used to wear this much??I learned to shoot clays with this and did not know the difference. I also made that custom forend about 1963

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Keith,

Is it possible that the relatively small and weak uderbolt spring of the Citori in the video has enough power to rebolt the lock up against the forces of the barrels being cammed open as well as their weight?

Personally I think not. I have a Citori and know how much the barrels weigh!

What actually happens to the shotgun action during firing is not at all clear. In the past I asked the super slo motion guys to do a clip of the action but they seem bent on the muzzle end which is visually more exciting.

One thought to ponder, anyone ever heard of a Jones underlever being cammed open? That would be a revealing as to what forces are acting and how on a SXS action during firing. My suspicion is that the Jones action would not cam open because the inertia of the underlever does not allow it, but I am open to any proof anyone might offer to the contrary.

It is also useful to include strong self opening actions in our thoughts, ie Purdey, Holland, and the added camming power during firing.

Shotgunlover, I agree that if the toplever, and the bolt, cammed open enough to completely clear the bolting surfaces, the gun would possibly begin to open and the bolt would not be able to go back home until the barrels were returned home.

You saw how much the top lever moved, and you know that would not be enough movement to actually totally unlock and open the gun. If the forces of firing could be sustained for more than mere milliseconds, the barrels would not rebound back and could continue to open the breech. But since the impulse is very short, and the bolt has not totally opened, the top lever spring certainly could return the bolt to full lock position just as it would upon normally closing the gun.

As Miller suggested, some guns have more tapered bolting surfaces than others. If Jones, Purdey, Holland, etc., ever developed a self opening gun that allowed itself to be popped open upon firing, they would immediately scrap that design and return to the drawing board. Guns that don't stand the test of time and guns that slowly self destruct end up getting scrapped. That's why we don't see too many loose Foxes or L.C. Smiths, and why we don't see too many tight Crescents or JABC's, even though they made a lot more Crescents and Crescent variants.

I cannot imagine any inertial force generated upon firing that would rotate a top lever to the right, can you? But there are all kinds of forces, vibrations, harmonics, etc. happening in that split second after the primer detonates. Hanging my pickup truck off the muzzles would certainly bend my barrels, but would not duplicate those firing forces. If there actually was such a left to right top lever rotating force, firearms designers could capitalize on it and design a gun that actually bolted tighter upon firing. I don't pretend to know the absolutely correct answer, but Miller's explanation of a tendency for a tapered rotary or under bolt to be partially cammed open upon firing still makes sense to me. I would love to see an absolute and irrefutable answer, and I'm sure that either you, Miller, or myself would be reasonable enough to accept whatever that turned out to be. Until then, it makes for interesting discussion.

"I cannot imagine any inertial force generated upon firing that would rotate a top lever to the right, "

Think of the stout sprng inside a Benelli bolt. It is compressed by the inertia of the rear half of the bolt during the first recoil phase. Compressed enough so as to unlock the action and perform primary extraction of a fired shell when the phase changes.

A top lever with more mass on the left side than on the right, and I have seen some so formed, at the end of the recoil phase, when the gun decelerates on the shoulder of the user would turn under inertia. I suspect the problem would be worse if the spring was also in line with the barrel axis.

In the Benelli autos we know the need to have the user's body to stop the main mass of the gun and thus initiate the second inertia phase, where the bolt travels back due to its inertia. Firing one from the hip can lead to failure because it does not allow the bolt's inertia to act.

Also think of how single triggers utilise inertia, though in smaller parts and weaker springs, or how safeties can self engage.

The camming open view somehow does not mesh with Greener, page 135 The Gun and Itse Development: "... the strain exerted by the force of the explosion is in a line with the teh axis of the barrels; to support this strain the double grip affords no power whatever. The work it [the double grip] does requires no particular strength. For the barrels may be held to the bed of the breech-action body by the thumb and forefinger, even though a full charge be fired". Greener seems to discount any camming force being exerted on double gun locking parts.

Definitely interesting topic. We need some high speed video of controlled experiments. A problem gun fixed to a free travelling bed to see if the opening can happen without the user's body stopping the main mass of the gun.

Or a more crude experiment of tying a problem "self opener" to slings and firing it. See if it would open under free and unhindered recoil.

OK, but a top lever on an L.C. Smith which is left of center, or even somewhat worn and at center, would not tend to rotate to the left when the gun suddenly decelerated during recoil against the shooters shoulder. And the top lever spring in a Smith gun is not tensioned in line with the bore axis. I see your point, but that would not explain an L.C. Smith or Ithaca N.I.D. opening upon firing, but camming of the rotary bolt would.

I agree that it would be interesting to see some high speed video of what actually happens at the moment of firing under various conditions and with various makes of guns. I'd also like to see a video of someone holding the breech closed on an unbolted gun with their thumb and forefinger during firing with a full charge as Greener suggests. But I am not volunteering my thumb and forefinger, having been peppered in the forehead with gasses by pierced primers, and once being totally blinded for about 20-30 minutes after a complete head separation on a .22-250 cartridge. Ouch!