Modern 66 / 73

[375Short]

In the modern Uberti/Taylor/Cimarron 66 and 73 toggle link action the same parts are used concerning bolt, toggles, pins and bolt extension. There are a number of things I don’t understand about this family and hope someone can take a few minutes to explain.

I understand looking at a 92 or 94 a chunk of steel rises into battery when the lever is closed locking the bolt forward against the cartridge base, basically. It is strong and easy to see how it works.

Where does the 66 / 73 get what little strength it has? What parts provide the strength to hold the cartridge into the breech when it’s fired? To me it appears the pins on the bolt, through the frame and perhaps lever share the load . It also appears that the frame simply contains the parts but doesn’t contribute to the strength except at the frame pin location and perhaps the lever. Is that the mechanical strength reason that the brass 66 and steel 73 almost are chambered in the same cartridges with the exception of .357mag?

If one of these two models survived an almost catastrophic failure from high pressure or prolonged wear and tear at what location does that appear in the action?

I have shot both for years and can take them apart and reassemble in a snap but I just don’t understand where it gets its strength to do its job. I like to understand. Im probably no the only one that will benefit from some enlightenment.

[cedestech]

The 66/73 models should not be used for high pressure loads.

Same parts, just 73 frame is made from steel as opposed to gunbrass.

The "lock up" is essentially the same as your finger or knee joint being locked and the straight back force is all onto a 1/4" piece of steel that the rear of the links toggle on.

They are cool guns and hold fantastic, lock time can be measured with a sun dial though...

[DAVIDMAGNUM]

This may help

1873 Cutaway.jpg

[375Short]

That is a great cutaway. Thanks for posting it.
It appears the weakest link is the hinge that joins the two toggle halves if visualizing the parts containing the rearward thrust of a cartridge when fired.I’m glad there are two. It also clearly shows why the addition of a lever (in battery) safety was a big deal in the 73 over the 66. History along with all the rifles new and old being used every day are a testament to a system that works but to the eye it looks like a frail trapeze act. Especially when compared to how other center fire arms lock into battery.

[Porpoise]

The frame takes the thrust through the links which are located by the pins. If the pins took the thrust they would not last long. Pretty sure if the pins were copper you wouldn't notice till they started to wear

[Rotnguns]

cutaway winchester 1873 Linkage.jpg

The pin joints on the linkage are more robust than they seem - they are "stirrup joints" that load the pins in double shear, as shown in the oblique cutaway above. Note that the middle pins are not highly stressed; the front links bear against the rear links as shown. The front and rear pins carry the load. But consider: SAAMI spec for a .45 colt is 14 000 psi; given an inner case head diameter of 0.48 inches, we're looking at an impulsive force magnitude of about 2500 lbf. From what I could find, linkage pin diameters are slightly less than 0.2 inches; not sure if those are the smaller or larger pins. In either case, machine dowel pins are easily able to support such a load in double shear, as shown from the McMaster dowel pin data sheet for 3/16 inch diameter solid dowel pins. Another possible failure mechanism would be crushing of the links in contact with the pins, but there's plenty of material for the pins to bear on.

[375Short]

Great education. Thank you. I better understand the system. My 73 and 66 copies are all Uberti’s. Having competed with, cleaned, changed a few parts and other general tinkering one learns that quality control and heat treating must not be of great concern at the factory. Screws are hard as cold butter. Numerous internal barrel issues through models I currently own and ones that have passed through my hands. I’ll just assume the links, pins and frames could possibly be of the same dubious craftsmanship and always error on the side mild loads for whatever cartridge they are chambered for. Kind of like owning a Travel Trailer, something always needs attention.

[Rotnguns]

Thanks for the information about the Ubertis. Sounds like you've got a very good understanding of how they work. I've never owned a Uberti, but I had the impression that they were well built. It's disappointing but I suppose, not too surprising, to learn that quality is taking a back seat during manufacturing.

[cedestech]

The frame takes the thrust through the links which are located by the pins. If the pins took the thrust they would not last long. Pretty sure if the pins were copper you wouldn't notice till they started to wear

(Says to self, why do they make me do this?)



Generic picture of a set of links (there are 2 of these, left and right).

You can see the holes in the links. One side has the pin that goes through the bolt, the other the frame.

When the link is “locked” it is stretched out flat (the 2 holes are as far away from each other as physically possible).

You will notice the round area of each link on the outside of where each hole is. This fits into a concave area ground into the bolt and frame respectively.

THEY DO NOT TOUCH. If they did, there would be witness marks and that area would need lubrication because it would be a tolerance fit.

Since they don’t touch, there must be some magical force keeping the bolt in battery if you are susceptible to believing in that… or maybe, it’s the pins since they are literally the only other thing in the gun attached to the links.

It is shaped that way so if a pin in the bolt or frame failed the bolt will jamb into the cavities of the bolt/frame and the bolt will stay locked as opposed to taking up the spot in your face your eyeball is using…

Do what you want, shoot the loads you want to shoot. I don’t care. There is a reason the 66 was replaced with the 73 (changing from brass to steel), then 92 and 94 (Marlin and Winchester) and a couple others and they all have bolts that “lock” with a chunk of steel that fouls the bolt.

I have no clue how mechanical things work so YMMV…

[Rotnguns]

Great picture, cedestech! Shows that there are actually four pins in the linkage we're discussing: the two front and rear pins that go through the parallel links on both sides of the mechanism, and the two smaller pins that hold the two links together on either side. I angled the attached image in an attempt to show this:

The two smaller pins holding the links together, as shown in your picture, actually are both stirrup joints loaded in double shear, but they each only take half of the impulsive force from firing because they each only connect one side of the mechanism; thus, they are smaller. I should have clarified this in my original post, rather than just saying that they were not highly stressed, which is not totally correct.

[cedestech]

My point is the area of the link A doesn’t touch the frame so no load is carried by it. The load is through pin B (and it’s twin on the bolt). Not shown is the frame and bolt have cut outs that “catch” the links if there is a pin failure. Also, the pin in the bolt and frame are one pin through the piece (bolt or frame) and the entire recoil pulse is being transmitted into the pin and frame by a piece of material a bit wider than 3/8”.

These rifles were not designed for high pressures/sharp recoil pulses and high round counts.

Are they cool? Yes. Are they fun to shoot? Yes. Can they be accurate? Yes. Should you hot rod them or even shoot hot modern loads out of them for thousands of rounds a year? I wouldn’t. Will they fail catastrophically ? Probably not but they will get sloppy and hopefully you’ll notice it before the fail safe design of the link to frame geometry gets demonstrated.

I just don’t want to see anyone hurt. Take my diatribe for what it’s worth.

[Rotnguns]

My point is the area of the link A doesn’t touch the frame so no load is carried by it. The load is through pin B (and it’s twin on the bolt). Not shown is the frame and bolt have cut outs that “catch” the links if there is a pin failure. Also, the pin in the bolt and frame are one pin through the piece (bolt or frame) and the entire recoil pulse is being transmitted into the pin and frame by a piece of material a bit wider than 3/8”.

These rifles were not designed for high pressures/sharp recoil pulses and high round counts.

Are they cool? Yes. Are they fun to shoot? Yes. Can they be accurate? Yes. Should you hot rod them or even shoot hot modern loads out of them for thousands of rounds a year? I wouldn’t. Will they fail catastrophically ? Probably not but they will get sloppy and hopefully you’ll notice it before the fail safe design of the link to frame geometry gets demonstrated.

I just don’t want to see anyone hurt. Take my diatribe for what it’s worth.

Actually, the links do indeed carry the impulsive firing load - they transmit the load to the pins and ultimately to the frame through the large pin at the rear. That's why they have to be quite robust - they must resist crushing failure at the interface between the pins and the links in the stirrup joints; they also have to be thick enough to avoid buckling. Fortunately, they appear to be overdesigned by a fair margin. Agree that they are fun to shoot, but certainly not at high pressure levels!

[cedestech]

My point is the area of the link A doesn’t touch the frame so no load is carried by it. The load is through pin B (and it’s twin on the bolt). Not shown is the frame and bolt have cut outs that “catch” the links if there is a pin failure. Also, the pin in the bolt and frame are one pin through the piece (bolt or frame) and the entire recoil pulse is being transmitted into the pin and frame by a piece of material a bit wider than 3/8”.

These rifles were not designed for high pressures/sharp recoil pulses and high round counts.

Are they cool? Yes. Are they fun to shoot? Yes. Can they be accurate? Yes. Should you hot rod them or even shoot hot modern loads out of them for thousands of rounds a year? I wouldn’t. Will they fail catastrophically ? Probably not but they will get sloppy and hopefully you’ll notice it before the fail safe design of the link to frame geometry gets demonstrated.

I just don’t want to see anyone hurt. Take my diatribe for what it’s worth.

Actually, the links do indeed carry the impulsive firing load - they transmit the load to the pins and ultimately to the frame through the large pin at the rear. That's why they have to be quite robust - they must resist crushing failure at the interface between the pins and the links in the stirrup joints; they also have to be thick enough to avoid buckling. Fortunately, they appear to be overdesigned by a fair margin. Agree that they are fun to shoot, but certainly not at high pressure levels!

Obviously… miss typed. I will endeavor to stay off this sight for another year or so…

Maybe Jason will come back and explain how silhouette will be restored to it’s former glory by the elimination of the score books…

[375Short]

I appreciate all respondents time and effort answering my question. I learned, others probably did as well.

[Rotnguns]

I appreciate all respondents time and effort answering my question. I learned, others probably did as well.

My pleasure! What else is a retired mechanical engineering professor to do Thanks for this most informative thread!