Most of my basculating firearms have a greener third closure, one has a Purdey nose, and one a Doll's Head. The BBF with the Doll's Head was slightly loose when I got it. How effective is it as a third closure compared to the others? is the "neck" connecting portion stretched, since it was indeed loose? Questions meditations. Steve
A well fit dolls head provides the draw necessary to prevent the forward thrust on firing that exerts so much force on the hinge pin. It is located at the point where it can offer maximum support. Other guns utilize a draw located at the front of the rear lump and engages the bridge in the action. So, in theory the dolls head provides the necessary restraining mechanism to keep the gun from self destructing itself. The problem as I see it is few were fit well enough to actually do what they were designed for. One notable exception would be the dolls head found on Westley Richards which offers maximum strength. I think some of the American guns, such as Lefever, also work quite well. So, yes the principle of a well fit dolls head is sound from an engineering standpoint.
Pigeon shooters ordered high grade Parkers without the doll's head for easier access to the empty shells. I don't know who first came up with the idea, but about all graded Parkers without doll's heads were of pigeon configuration. They apparently knew that the doll's head was not neccesary to keep their guns together.
Well fitted and with the necessary bite they are effective . But like all mechanical devices they need to be kept in good order and if the rest of the joint comes slack then so does the dolls head [club head , spade head ] . Problem is that on 100 year old guns that have not been well maintained or been to the local black smith ,no slur on blacksmiths here , then no it will not be much good . Point of fact I have rarely seen a cross bolted gun in which the cross bolt actualy serves a useful function and many from which they have been removed .
Errm, if the Rigby rising bite classifies as a "dolls head" then I think we can take it as a given that it adds strength as it is universally recognised in the trade as the strongest double rifle joint but was so expensive to produce it was abandoned. The Westley Richards dolls head is a masterpiece too, just my opinion (Iīm not saying you need them, just that they are tough. I actually donīt like them on dangerous game doubles as I think they might slow down reloading but if you ever get the chance to see a Rigby rising bite in function it is a wonder ) best
Joe Wood has hit the nail on the head. I think the reason so many claim they do "Nothing" is that they in fact do absolutely "Nothing" to prevent the bbls from opening. That of course is not what they were designed or intended for. The Lefever uses a Doll's head with square front shoulders, which I feel is good as they have no tendency to wedge open their seat. On one parts Lefever I have which is in quite rough overall condition & on which the adjustable ball joint has been loosened I can back it up so it clears the hinge socket, close the gun & bolt it & it is tight on face from the Doll's Head alone. If fired a lot with only this support I don't know how well it would hold up, but working in conjunction with the hinge then it gives support on both sides of the chamber, IE both top & bottom, it will take an awful lot of proof to convince me that is not a good thing, even if the frame is strong enough to hold the forces in & of itself.
The French Ideal has a dynamic doll's head, with reciprocating wedges rising to engage the barrel extension. The shape is such that the joint is always tight, the parts wear in, keeping contact through the years. Most other doll's heads are kind of delicate affairs with static fit and no provision for wearing in.
The theory is that the doll's head resists the backward bending of the action on firing. Notice that no authority analyses what happens after the action has bent backwards. My guess is that if it does indeed bend, then it springs back to the original position with some force. It becomes a hammer, and so we must ask what is the "work" being hammered and what part becomes the anvil.
The traditionally held belief that the cartridge case pushes on the breech face by itself, and the barrels remain static, is a little suspect. My (unproven as yet) view is that barrel and cartridge become a single unit and both together push against the breech face. Indications that this is so are the imprints left by the barrels on the breech face.
If the barrel and cartridge push back together, then there is no need for any third bite. As people have noted on anothr thread, a double can be fired with no bolting in place, a sign that there are no forces acting to separate barrels from action during firing. And if this turns out to be correct then there is no role for any doll's head, not even the super tight fit one on the Ideal.
A few thoughts on this theory. "IF" the gun is tight & on face & the barrels & cartridge come back together there should be no "Hammer" as the parts are already in full contact with the breech. "IF" on the other hand the breech springs away giving a gap & then springs back forward till it hits the barrel breeches this could account for the imprint on the breech face just as well as if the barrels hit it. A good test of this theory is to remove the bolt from a Browning A-5 & fire it & see if the barrel & bolt recoil together as they do when locked. You can do the firing though, I'll Pass. The other thread incidentally is referring only to the rotational portion of the forces & has nothing at all to do with this axial thrust. "IF" everything worked as in your theory then you should never see a frame cracked at the bar & breech junction as there would be no force there.
If you take a serious look at the dollshead on a Parker, you'll see it's of little value in terms of adding any strength. What it does provide is the guide slots for the individual ejectors and the stop for them. The crossection remaining after considering the slots and necked area, is very small.
As for the need for more locking strength, I beleive the forces trying to separate the barrels from the breach are relatively small.
Well fitted dolls heads, side clips, hinge joints, cross bolts, under bolts, rotary bolts, under lugs, etc. all will contribute to a tight and long lived action, as does good action design. When these features are poorly done, the forces of firing begin the process of beating the gun to death starting with the first shot. Well made and well designed guns stand the test of time. Cheap guns quickly become rattletraps. The proof is in the parts boxes at every gun show. Although many more cheap Crescent and cheap Belgian doubles were sold at the turn of the last century, there are many more of the higher quality guns still in everyday use today.
The net is sprinkled with clips of people firing zip guns made with two sections of pipe and they hold OK. Richardson industries even offered such a gun which was basically two pipes fitting into each other with no bolting of any kind. You might be surprised as to how an A-5 would behave if fired unlocked. Provided the chamber is not highly polished I would be willing to fire one, you can watch from a safe distance.
Frame cracking occurs, I have photographed a few such accidents. The question is why the frame broke, because it was pushed back by the cartridge head alone? Has anyone ever figured out the Poisson effect and its contribution to the firing cycle of a shotgun barrel? The Poisson effect covers the radial expansion and axial contraction of thick walled cylinders under pressure. The breech end of shotguns falls within the definition of thick walled cylinders. Can such rapidly developing dimensional changes, even though small, affect a shotgun action? If so how?
How come some US made doubles with apparently weak lockups (L.C.SMith, Lefever) hold up over the years when triple bolted doubles shake loose?
These and other questions are puzzling. If some high speed photographers could film the action we will get an idea of what actually happens during the firing phase and the recovery from it. But most of them prefer filming more sensational shots of the shot exiting the muzzle.
SGLover; I realize there are many differences of opinion on a lot of things, but personally I do not consider the lock-up on either an L C Smith or the Lefever as "Weak". It is true that each has only one bolt, but that bolt is situated as far as possible from the hinge taking advantage of the extra leverage & quite obviously has proven to be entirely adequate on both. If you do a smoke test on the fit of guns with all those multiple bolts you might be surprised at just how many actually fit & thus provide anything at all useful to the bolting. This will be especially true om anything other than a very expensive & well fitted gun. The vast majority of US made double rely on only a single bolt to hold the barrels closed. In the US many, many more guns were sold to "Commoners" than in the UK. The US makers "I Think" wisely concentrated on a single adequate bolt to keep the thing shut & did so with great success. It is also noted that .22rf & many low intensity handgun cartridges in semi-auto form all operate on the "Blow-Back" principal, IE an unlocked bolt is blown back out of the chamber by the cartridges back thrust. As the cartridge's intensity increased it became necessary to go to a locked breech design. One old Spanish design by Astra did use a blow back design for the 9mm Largo & a few in 9mm Parabelum by the use of an extremely heavy bolt to slow down the back thrust simply by its inertia. This is also the principal by which the famous "Tommy Gun" operates chamber for the .45 ACP round. I "Very Seriously" doubt that an ordinary shotshell case has enough Grip on the chamber walls to make them a single unit as such.
All SKB, Miroku, Browning and most other modern production SxS use a double underlug, no extra bolting. Never have seen one get loose from shooting modern full pressure ammo. A few damaged by lack of cleaning/lubrication or stupidity. Merkel uses a cross bolt and the double underlug, the crossbolt is probably not needed. The most basic lock up of modern guns may be the Stevens/Savage 311 and variants. These guns get good mileage.
I would also like to see high speed pics of just exactly what happens when the gun is fired.
Interesting point about blowback actions. But if you recall one of the problems in blowback actions was case sticking, and one of the ways invented to overcome it was the grooving of the chamber which allowed gases to surround the case and thus equalise external and internal pressures.
The blowback cycle starts once the inertia of the bolt has been overcome and by that time the bullet has left the barrel, pressures are at about zero. I suspect the same would happen in an Auto 5 without bolting if the chamber is not polished slick.
An interesting point about zipguns is that they keep together as long as the "barrel" mass is such that it does not overpower the frictional grip of the case on the "chamber" walls. When a heavy "barrel" is used then the "bolt" pipe does fly back smartly. This much is viewable on Youtube.
I am not advocating the manufacture or use of these abominations. But their behavior gives some interesting clues about what happens when a shotgun is fired.
American made shotguns are not weak, I did not mean to imply this, I did not express myself well in that post. On the contrary, they are plenty strong. However to the European conditioned shotgunner the single top bite seems weak. We Europeans assume that the only proper bolting for a SXS is via unerbolts, possibly aided by a top extension.
The simple practical top bite is not the only area where US makers pioneered new and possibly better ways to do things. The Lefever ball joint is a brilliant example of design foresight. It avoids all that messing about when it comes to tightening a loose shotgun. Amazing that it was not copied, but perhaps not, European makers tend to suffer from "mental inertia" as Gough Thomas pointed out.
Well I have semi-auto pistols in .22LR, .32ACP & 9mm Makarov by Ruger, Colt, Walther & East German in the case of the Makarov, forget the exact maker. Not a single one of these has any grooves in the chambers or anything else special about them. They will all function reliably even with a dry chamber. I think those grooved chambers were for some special experimental uses which never really took hold. ""IF"" the bolt did not move prior to the bullets exit, it would not move at all. It is true it will have only moved a very short distance prior to the exit, but that movement is sufficient to impart the necessary inertia/momentum to the bolt to continue its rearward travel. When the projectile exits the muzzle the gas rushes out dropping the pressure instantly, if that bolt had not already received its rearward impulse it certainly would not receive it then.
We definitely need a slo-mo film of the action on firing. I left a message to the slo-mo guys who post on Youtube but so far got no reply.
Whatever happens to a break action during firing I feel that it is not what we have been told so far, that the breech face receives a hammer blow from the cartridge head, which flexes the action back, and the explanation stops there. If it does go back it must recover. It does not just gape open from that point on.
A slo-mo sequence might help us understand why some guns shake loose and some do not. And it might surprise us about the utility of third bites and fitting on the circle etc.
This is not quite what you are looking for, but it does suggest strong backward force by the shell casing against the breech (watch the second iteration of this "experiment" in the second half of the video).
Totally agree on that Shotgunlover. I'd love to see such footage. Many people have argued aboud third bites and their construction and that is based on one's understanding of the physics, not real data. The people who have some real experience are the one who made long lasting shotguns & double rifles that were shot a lot and whom staid in business for a long time. Westley-R comes to mind as an example.
There are usually two ideas behind the 3rd bite. - the first one is to keep the gun shut (Purdey et al.) - the other one is to keep the action from flexing under the backward force at the breech. This is a clear fact of life as otherwise nobody would be rounding the action root. The old doll's head without bite only tries to address this second phenomenon.
Some third bites do both: Greener (not the best), Webley screw grips ,Rigby Bissell Rising bite ,Ideal , Westley Richards C bolt, etc.
Of course, the best doubles to investigate this phenomenon are not shotties, but double rifles.
As was mentioned; IMO all the gizmos work if fitted correctly. Were they possibly dropped mainly because of better metal developement and of course cost?
The Beretta 680 series over under with removable and replaceable side thingies is an example of a useless extra that actually does what it is advertised to do when fitted properly. When fitted properly, the barrels are actually cammed toward the breech and stay in the cammed position while in the firing position. You can actually feel the barrels tightening up against the cams as you close the gun. On guns without the replaceable cams, or on guns with barrels that did not come on the action being used, you can't usually feel the beginning of the camming action. The camming action is so slight that the trunnion contact is not lightened to any extent and you have full contact at both the cam and the trunnions. The 680 series action is so "correct" that the fitted thingies are not used in lower end guns and their longevity record is as good as the more expensive models. Kind of like Purdeys with and without side clips and third fasteners. By the Beretta action being "correct", I mean that the trunnions and the cams only serve to add to the locking lugs that protrude from the receiver and plug into the barrel breeches. I think the gun could be safely fired with any two of the features deactivated. It would be an interesting experiment.
Obviously the "Springing Back" of the standing breech upon firing does not exceed the elastic limit of the steel, or it would remain gaped. W W Greener did tell about fitting one of his guns up so that instead of the cross bolt being moved by the lever he simply fitted it with a knob so it could be inserted or removed by hand at will. He fitted a strip of brittle mat'l between the bbl rib & breech. Firing several ordinary service loads up to the max with the cross bolt removed did not break the strip. He continued with heavier loads un til he did begin to break the strip. He then began inserting the cross bolt & continued on with still heavier loads with no further breaking of the strips as long as the cross bolt was in place.
The Greener experiment and Field magazine trials are echoed by Gough Thomas, who also did the dot of plasteline on the action flats experiment.
What would be useful is an experiment that would exclude the Poisson effect as the cause of the phenomena observed.
The plastic limits and recovery of the action during bending imply a forceful process. I am wondering if the recovery of the action body delivers a hammer blow to the barrels, pounding them onto the cross pin.
I also wonder if cheap folding guns, where the barrel lumps are trapped in place via a through cross pin, avoid this pounding. Folding guns seem to be less prone to shaking loose. But that might be a false conclusion drawn from the ones I examined.
The practical reason for my preoccupation with these things is that a clarification would allow more robust design and safer repairs. It is not just theory.
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