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

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.