doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com How to tighten a Smith

Guess the fella smacked the lug a little too hard





Thanks to Norm for the alert

Cool I didn't know the hook was brazed on! MKII

The hook, spacer, top rib and extension are all one piece; shown on this radiograph



The joint is apparent on this Trap Grade



Pre-1913 No. 2 with a silver spacer

Why would someone have to "tighten a Smith"?? Their ads all said "never shoots loose"!!

The more you shoot a Smith the tighter it gets! Bobby

Maybe it got so tight the hook broke off!?!?

Even an LC Smith can only hold up so many fully loaded tractor trailers or so many twenty story buildings.

Maybe when someone was out hunting, they needed it as part of a tow bar to get a broken-down vehicle home.

At least it has been elegantly repaired to original condition.
CHAZ

"Maybe when someone was out hunting, they needed it as part of a tow bar to get a broken-down vehicle home."

Every time. Never fails, and I always hate that crap, "Look, he has an LC Smith, ask him"

Many thanks to David Elliott who dissected a hopeless Smith barrel showing the hook and rib extension are not one piece, and are indeed brazed.

"The extension and hook are two separate pieces, not one as the X-ray seems to show. The barrels are milled to the required angles and the extension and hook are fit to create the assembly. The extension has a locating pin that fits into the hole created when the barrels are put together. The hook comes in from the bottom and the assembly is complete."

That's kind of disappointing.

That is not so hard to believe it is in two pieces, time is money and to make that in one piece would be very expensive to machine.
I thought in Brophy's book it showed that "V" cut but was not clear enough to show everything.

Not only that, but this design has stood the test of time, and passed with flying colors. How many others have you seen that have either the rib extension or underlug breaking loose? In Sherman Bell's Damascus testing, the barrels blew up before any of these brazed joints failed.

In Buck Hamlin's destructive testing of Damascus, a badly pitted old L.C. Smith was blowing open upon firing with extremely heavy "nuclear loads", but the barrels held. I have often wondered how a rotary bolted gun can blow open without either breaking the rotary bolt or the recess in the rib extension. That part was never explained.

The rotary bolt opens due to pressure on the slopping surface camming it around, sort of like squirting a watermelon seed. Different makers used different means to prevent this occurring in their designs, but this seems to have been a major problem with the otherwise excellent rotary bolt.
Winchester used a very shallow taper on its underbolt so the friction preventing it moving was greater than the force trying to move it. To keep it from sticking making it difficult to open they placed the stop screw in the notch. With their underbolt Parker Bros used a steeper taper which eliminated sticking, but to prevent the gun opening they used little side rails with parallel surfaces. If te bolt opened even the slightest these parallel rails on the bolt & luig came in contact thus preventing further opening. I have never owned oine but from what I have heard the Ithaca NID rotary bolt seems to have been more prone to opening with ordinary loads than was the Smith, not sure how the Fox fared on this aspect.

The rotary bolt moving under pressure makes sense to me, as I had a LC Smith that would partially open when fired. It was a weak top lever spring, replacing it fixed the problem.
CHAZ

Treblig 1958
It may seem disappointing that the extension and hook are separate pieces but I can assure you the assembly is incredibly strong. The ribs and spacers came off easily with a Bernz-o-matic tourh and Mapp gas. Anyone can do this in their garage. The hook is held with a top plate and screw. It too had a small amount of brazing but was mostly held with solder. The barrels were then clamped by the hook securely in a vise and heated with oxy/acetylene. I was amazed at the amount of heat it took to get this thing apart. The lines of the individual parts did not appear until the thing was approaching a bright orange. I had to soak it a good three or four minutes, pulling and pushing on the tubes before I got any movement at all. Once apart, I was very impressed by the design and fit of the parts. I'm guessing that it was fit up in a jig and furnace brazed, ribs and such added later. I'd like to know the history of the barrels in the beginning of the thread but under normal or heavy use I don't see how they would come apart.

Dave Elliott

"The rotary bolt opens due to pressure on the slopping surface camming it around, sort of like squirting a watermelon seed."

The slope in locking surfaces is around 6 to 7 degrees. I find it hard to believe that the forces tending to throw a double gun open are so great that they can force such shallow angled surfaces to act as cams.

If those forces were so great doubles would not be able to fire when held by two layers of scotch tape (per Gough Thomas), or no locking bolt in place (Greener).

More likely is the design that locates mass in the "wrong" place so that the inertia during recoil gets the parts moving. Note how Hoof reports fixing his opening problem by replacing weakened springs. This echoes my experience with this problem.

Slow motion videos on Youtube show that the opening levers and hammers (of hammerguns) oscillate under recoil. And let us not forget that inertia in Benelli autos is strong enough to compress a stout recoil springs that cannot be hand compressed.

I'd always assumed that the lug was one piece. But I now see how the barrels were constructed. The barrels don't appear to be beat on any more than other O grades. So,the presumption is that extreme heat caused the cracks?

The inertia of a bolt acting axially with the bores is subject to the forces you mention. The rotary bolt has no motion which would be moved in an opening direction by inertia. I am not an engineer, but seem to recall that around 7� is the point where friction is about equal to applied force. I believe one problem with rotary bolts is that the angle actually increases across the locking area due to the decreasing radius to build in the wear compensating taper. If the bolt is not absolutely perfectly fitted it can end up with more pressure out to the right side of the lug where the taper is greater. Elmer keith once reported on an Ithaca 10ga NID which he said was the "Most Automatic Gun" he had ever fired. Upon pulling the trigger it fired, opened & ejected the empty. He sent it back & they refitted the bolt & cured it. They "Did Not Change the Moment of Inertia" by simply refitting the contact area of the bolt. A stouter spring of course increases the forces necessary for opening the bolt whether it be from inertia or otherwise.

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!

Being virtually strictly a SxS man I am not really familiar with how the Benelli operates. That said however all mechanisms with which I am familiar which operate by inertia have the inertia parts aligned axially with the bore or very nearly so. This is true of single trigger inertia blocks as well as the bolts of recoil operated guns, of which I do have several, just not shotguns. The rotary bolt on a Smith, Fox or Ithaca is set in line with the bores "But" it rotates at right angle to that line. There are no inertial forces acting in that direction.
The inertia on a sliding underbolt would actually tend to tighten it upon recoil starting, but would transfer to opening as the guns recoil was stopped by the shooter.
Greener was of course extolling the virtues of his Cross Bolt in his statement. It must be fully realized the "Back thrust" of the firing is directly in line with the bore axis. Since the hinge f a normal double is below the barrel line then some of this force is transferred to an opening action, though not as great as the direct force placed upon the standing breech.
"IF" of course there were no case head thrust there would be no need for any bolting at all except just enough to keep the gun closed for firing. The action could as well be made of a piece of pine. I think a bit of thinking & common sense will show this is not the case.
Greener did further show by firing his gun with the cross bolt made so as to be placed in position or removed by hand that his action was strong enough to hold all normal loads without the cross bolt. he did this by placing a non elastic strip across the gap securely held on both sides. upon increasing to heavier than normal loads he began to break this strip without the cross bolt but with it in place could load still heavier & did no succeed in breaking it with any load the gun would otherwise stand.

One other thought worth mentioning which I have not stated up until now. The rotary bolt on the smith & I presume also on the Fox & Ithaca are tapered in two directions. inside of the bolting finger is tapered so it draws the barrel down tighter to the frame while the back surface of the finger is tapered so it securely bolts the standing breech up to the barrels. "Both" of these surfaces need to be precisely fit so there is an equal bearing upon both. As the loads increased above normal loads on this Smith that Buck was testing it may as well have been the frame flexing enough to cam the bolt around rather than the opening. Once starting to rotate the bolt the barrels could then begin to open & both forces might well work together to cause the gun to open. It would indeed be interesting to know when Elmer Keith sent his 10 gauge NID back for re-fitting of the bolt to know for sure just which surface they had to re-work.