Conversion Cylinders ... Safe?

[hickstick_10]

its not the impact of the ball im getting at. its the pressure BEHIND the ball, if there wasn't a few thousand psi behind the ball, it would never leave the barrel. And this creates a pressurized connection between the cylinder face and the barrel breech, like 2 steam pipes butted/joined together which when you take pressure multiplied by cross sectional area of the bore, gives you the force which is trying to push the barrel away from the cylinder.In the pressure behind the ball idea I would have thought the Remington would win hands down

So many firings, puts so many cyclic loads on the wedge, I'd rather rather have a solid frame of steel with a threaded barrel taking the loads, then glorified piece of sheet steel. The open tops win the looks category hands down though, I think the Remington style is damned hideous.

But like I said, im just a student, il keep tinkering with the free body diagram, at least until it points that im FOS (when im not swamped with godamned homework):barf:

 

[Dino.]

Okay, I emailed Cimarron Sales (Chiappa) and asked ...

"Can you please tell me if the 1872 "Open Top" pistols are built to handle modern loads? Or are they restricted to "cowboy loads" only?"

Their response ...

"They are made to take standard factory ammunition, not just cowboy loads, but not plus p either."

 

[Ben Towe]

A box is stronger than a U. There's your answer. I'll agree an open top is more pleasing to the eye though.

 

[Dino.]

A box is stronger than a U. There's your answer. I'll agree an open top is more pleasing to the eye though.

I would think this has more to do with the walls of the cylinder as opposed to the construction of the frame.

If the cylinder can't handle the load, it doesn't much matter how the frame is constructed, does it?

 

[w_houle]

Meh, I just shot whatever was commercially available through my R&D.. Usually this
https://www.budsgunshop.com/catalog/product_info.php/products_id/66102
The only problem I have with .45 Colt is it has a standard OAL of 1.6" and the cylinder likes them at 1.58". So I usually spent the time waiting on those I go to the range with filing bullet noses down to make them fit.

 

[Hardcase]

A box is stronger than a U. There's your answer. I'll agree an open top is more pleasing to the eye though.

All things being equal, I agree with you. However, there is "strong" and there is also "strong enough".

 

[mykeal]

A box is stronger than a U. There's your answer. I'll agree an open top is more pleasing to the eye though.

Maybe. And maybe not. Depends on the size of the members, the materials used in their construction, how the loads are applied and many other factors.

But, in this context, you've misidentified the design. The open top Colts are not a 'U'. You've failed to consider the role of the arbor, wedge and the lower receiver/frame joint. Draw the COMPLETE structural diagram, then take some cross sections, apply the loads and construct the free body diagrams and then see what you get.

 

[zippy13]

Because I've done the free body diagrams and can see how the loads are distributed.

If you assumed a reasonable application of loads, then you realize (because the geometry of an open top revolver results in a cantilever reaction) the center pin resolves all the load while the bottom strap serves to stabilize the cantilever. If the pin is in tension, then the bottom strap is in compression. With a full frame revolver both straps work together to resolve the load (the top strap taking more than the bottom since it's closer to the barrel and the center pin is not involved since it isn't fixed).

The cross-sectional area of a closed frame revolver's straps greatly exceed that of an open top revolver's center pin. Consequently, the corresponding unit stresses will be significantly greater in the open top's center pin given the same loading. (Actually, it's not the total area of the pin that's critical, but the contact area of the wedge.)

Since a closed frame revolver operates at much lower unit stress than a comparably loaded open top model (and, I've ignored the fact that a closed top revolver has moment resisting connections where the open top doesn't), IMHO PetahW's expression "inherently stronger" is appropriate. That's my two-cents worth.

 

[mykeal]

The cross-sectional area of a closed frame revolver's straps greatly exceed that of an open top revolver's center pin.

That's simply incorrect.

a closed frame revolver operates at much lower unit stress than a comparably loaded open top mode

And so is that.

 

[zippy13]

mykeal,

The cross-sectional area of a closed frame revolver's straps greatly exceed that of an open top revolver's center pin.

That's simply incorrect.

You may be correct, let's have a look…
I'll compare a Colt Navy replica with a '58 Remington replica. The diameter of the Navy's pin is 0.424" giving a gross area of 0.141 sq. in. The wedge cut-out reduces the gross area by 0.06 sq. in. to net area of 0.081 sq. in.

The '58 Remington's top strap has a gross rectangular area of 0.189 sq. in. A sighting channel and chamfers reduce that to a net of 0.171 sq. in. The irregular bottom strap is smaller with a minimum net area 0.036 sq. in., resulting in a total net area of 0.207 sq. in.

It seems you are simply mistaken, the closed top model has over 2-1/2 times the net area of the open top. IMHO, a factor of 2.5 justifies my use of greatly exceeds to describe the difference. Of course, your specimens may provide different results.

a closed frame revolver operates at much lower unit stress than a comparably loaded open top model

And so is that.

Early in my engineering studies, we learned one of the basic building blocks: P=F/A (unit stress = force/area). Material selection is typically based on its maximum allowable unit stresses. A doubling of the area halves the unit stress is a concept I've applied throughout my professional career. Its universal application includes firearms. Consequently, based on the dimensions of my specimens, for the same load, the Navy Colt will have about 2 1/2 times the unit stress of the '58 Remington. Perhaps you have a different perspective on one of engineering's basics.

 

[arcticap]

Consequently, based on the dimensions of my specimens, for the same load, the Navy Colt will have about 2 1/2 times the unit stress of the '58 Remington. Perhaps you have a different perspective on one of engineering's basics.

When fired, isn't the "exit stress" exerted on the Colt by the projectile focused on the small surface of the wedge where it mates with the inside edge of the arbor slot, and also where the slim end of the arbor is mated into the frame at the back of the recoil shield?

By comparison, when the Remington is fired the barrel is being secured in place by virtue of it being threaded in to the steel housing of the frame that surrounds it.

If what you're asserting about the "frame" is correct, then is that even applicable?
I'm asking because the assertion doesn't explain why Colt arbors seem to more than just occasionally loosen up over time while the Remington barrels do not. And that doesn't only happen to the brass frame Colts but also to the steel frame Colts too.
So then what does make the Remingtons appear to have a stronger and more secure barrel/frame attachment system verses the Colt? The notion seems to be based on an actual structural weakness of the Colt's barrel/frame attachment.

 

[zippy13]

Arcticap, you've hit the nail squarely on the head, it's the connections that are critical. Engineering failures are more likely to occur at the connections. Those unfamiliar with the connection alteration that resulted in the Hyatt Regency walkway collapse might find Wikipedia's entry interesting.

One of the members took exception to the comment, "A revolver with a top strap is inherently stronger than any open top," and was going on, ad nauseum, to substantiate his position. When he got to the point, "Because I've done the free body diagrams and can see how the loads are distributed," I felt it was getting way too deep and it was time to clean out the barn. Comments by others indicate that I'm not alone in questioning the application of free body diagrams.

Since the most obvious difference between the designs is the top strap, I limited my comments to the straps. Free body diagrams might be used in the 19th century to determine the strap reactions, and subsequently the forces in the connections. Most are aware that problems associated with the open top design typically occur at the connections. My brass navy replica was retired because of connection problems.

Unfortunately, I didn't realize that I was feeding the troll when I stated, "The cross-sectional area of a closed frame revolver's straps greatly exceed that of an open top..." Can you imagine my surprise when the member responded with, "That's simply incorrect."? Rather than respond in kind with, "Liar, liar, pants on fire," I took the time to take the appropriate measurements to calculate the areas to substantiate my position.

Back on topic: If I was interested in a cartridge conversion based solely upon the strength of the cap and ball's design, my choice would be the Ruger Old Army. Yeah, I know, it's not period appropriate, but the frame is hell-for-stout.

 

[mykeal]

Here’s my observation: 1) Deleting the slot area in the Colt arbor is invalid as the slot is partially occupied by the wedge. Arbor pin loads are transferred to the frame and vice versa, bypassing the open area. Note: if the wedge is not effective in transferring loads the pin would carry no load at all, since the cylinder is free to move axially on the pin. Thus the entire diameter of the arbor pin (0.1466 sq in) is effective in carrying loads. Colt arbor: .436” diameter, thus 0.1466 sq in area.

2) Your analysis ignores the Colt lower frame joint, which is effective for all loads except tension. Application of basic free body load diagrams shows that this joint carries compression and bending moment loads when the revolver is fired, thus it’s area (0.0983 sq in) is effective and must be included. Colt lower frame: 0.237” X 0.415”, thus 0.0983 sq in area

This gives the Colt design an effective area of 0.2449 sq in.

My inspection of the Remington design, based on measurements of a .36 cal Pietta specimen, gives 0.1845 sq in for both the Remington straps (0.1461 sq in top and 0.0384 sq in bottom), but I’ll accept yours as valid for your specimen.

So I see the Colt as having the higher effective area by 0.2449/0.207 = 1.1832.

I do most certainly agree that doubling the area halves the stress if the load is the same. The problem with your statement was, as I saw it, the error in comparison of the two effective areas, not the principle you identified. My comment still stands based on my presentation above.

Arcticap’s discussion is interesting. He’s absolutely correct in his observation that the Colt loads are carried through the arbor to the recoil shield; there are components carried through the frame by the lower frame attachment as well. Remington barrel loads are transferred to the top and bottom frame straps at the barrel/receiver joint, then via those straps to the recoil shield. The only part of his discussion I’m in disagreement with is the observation that Colt arbors “seem to more than just occasionally loosen up over time…”; I don’t have that impression. It’s certainly not my experience, as I own a number of Colt open top revolvers that I’ve shot thousands of rounds through over some 35 years; none have loose arbors. Certainly the brass frame open top Colts have this problem, but I believe that’s a materials problem combined with abuse, and it’s not present in the steel frame guns. I’d like to see data on that if it’s available.

As regards the Ruger Old Army, we agree on that point. It’s clearly, in my opinion, the best (including ‘strongest) black powder revolver ever made by anyone at any price.

Finally, let’s agree not to use pejorative language, such as ‘ad nauseum’, ‘feeding the troll’ and ‘Liar, liar.’ My comment (“That’s simply not correct’) was a simple declarative with no personal prejudice involved. It contains no reference to your person, intellect or personality and doesn’t merit name calling in response.

 

[zippy13]

mykeal,

Sorry about the pejorative language. When you responded without any data my troll-o-meter went off. I'm curious to see where our basic differences arise. I'll make some observations and you can send up a flare when you don't agree, okay?

Our area of concern is how the loads are resolved in a open top Colt F-model compared to a closed top model, in this case a Remington model of 1858. The question at hand is the unit stress in the elements that transfer barrel loading to the frame (or the rear portion of the Remington's frame).

The R-58 has one piece frame unit with a large central opening bounded by top and bottom straps that transfer the load between the front and rear portions. The cylinder pin is free floating and doesn't resolve any portion of the load.

The Colt F-model has an "L'' shaped frame with a cylinder base pin. Loads from the barrel are transferred to the base pin via a wedge in double shear and to the lower portion of the frame (strap) via a simple bearing surface with two locating pins.

During the firing event, a load is first applied to the barrel as the ball departs the cylinder and contacts the barrel's forcing cone. Until the ball exits the muzzle, the barrel and chamber act together as an expanding-volume pressure vessel (with leaks at the forcing cone gap and nipple hole). The majority of the pressure is taken by the walls of the bore and cylinder with some reacting against the base of the bullet and the back of the cylinder. This generates equal and opposite forces between the barrel and the back of the cylinder, and puts the barrel's restraint in tension.

In the R-58, the barrel's forward load [P] is transferred to the front frame section via a threaded connection. Then, the two straps distribute the load to the rear portion of the frame. Since the bore is unevenly spaced between the straps (see schematic, below), the upper strap carries roughly .75P and the bottom .25P. Using your numbers for the area, this equates to a unit stress of [.75P/0.1462] 5.13P psi for the upper strap and [.25P/0.0384] 6.51P psi for the lower strap.

With the Colt F-Model, the barrel's forward load is transferred to the barrel wedge and to the lower strap bearing surface. As is typical with all bearing surfaces, the lower strap can transfer only compressive loads (the pins are for locating and aren't moment resisting). Since the barrel isn't located between the reactions, the load can be resolved as a cantilever (see schematic, below). Using the dimensions of my specimen and your numbers, the base pin is in tension 1.625P with a unit stress of [1.625P/0.1466] 11.08P psi and the base strap is in compression .625P with a unit stress of [.625P/0.0982] 6.36P psi. Note, the stress in the base pin will increase at the wedge-way.

From this, it appears the Remington's maximum unit stress is (6.51/11.08) about 59% that of the Colt.

 

[Delmar]

Arcticap, you've hit the nail squarely on the head, it's the connections that are critical. Engineering failures are more likely to occur at the connections.

This would the case, especially in an open top that came from the factory with a poorly fitting arbor, as some do. Given what I have learned, I would never put a conversion cylinder in an open top, without making sure the arbor fit well first.

 

[arcticap]

I don't know about which frame is stronger in theory and on paper. All I know is that arbors can loosen up.
I found at least 2 folks reported having loose arbors with their steel frames here and many more having brass frames.

Madcratebuilder has one .44 and Oquirrh has one in .36:

http://thefiringline.com/forums/showthread.php?t=390305&highlight=loose+arbor

http://thefiringline.com/forums/showthread.php?t=353239&highlight=loose+arbor

From reading it becomes apparent that sometimes there are alignment issues with the arbor not being parallel to the bore and problems with the arbors being either too long or too short. When they're too short the wedge literally bends the arbor upward and closes up the barrel cylinder gap.

There's issues with the cylinder repeatedly slamming into the recoil shield and exerting even more stress on the arbor attachment, and the arbor attachment methods used by some manufacturers differ to where some can loosen.

You'll only have to worry about it if or when the wedge gets hammered enough to indent or bend it do to a cylinder gap slammin' the recoil shield and forcing cone back and forth till it breaks the locking pin on the back of your abor and the arbor rotates loose.
Other than that there's not alot to worry about.

http://thefiringline.com/forums/showthread.php?t=352233&highlight=loose+arbor

The crux of the Colt arbor and frame strength issue clearly becomes more glaring if comparing the brass frame Colt to the brass frame Remington. The brass frame Remington appears to have a better track record than the brass frame Colt. I don't think that it's as much of an issue about the relative strength of each of their brass frames but rather about trying to identify the relative weakness of each of their designs.
With the Colt design, the arbor & frame is subject to more stress forces than the Remington due to all of the well known alignment and manufacturing issues including the strength of the arbor, wedge and attachment points.

Just look at the relative amount & diameter of threading of the Remington barrel verses the threading of the arbor at the back of the frame if there is any arbor threading at all.

That's not to say that Colts are bad or weak or anything else. It's a safe design, adequately constructed and they work quite well. And its not about bashing the Colt but trying to understand why people think and then say that the Remington top strap design is stronger.
The Remington design seems to be stronger vis-a-vis the amount of shooting stress that it needs to endure, whereas the Colt doesn't seem to be as strong considering the amount of shooting stresses that it needs to be able to endure.
And I do want to emphasis that the Colt seems to need to endure more shooting stresses because its design is more complicated and harder to manufacture as well which results in everything not lining up as well.

I really don't care if it's one critical part or many, but there are weaknesses that aren't reflected on paper when examining which frame is stronger.
And it doesn't matter which frame is stronger. When folks say that they think that the top strap design is stronger, they really mean that the Remington design seems to be more durable. Whether the top strap itself is stronger isn't really the issue.
It's like trying to correct a person's English.
We all know what people mean when they say that the top strap frame is stronger.
It means that the Remingtons tend to have less problems by virtue of their stronger design.
While the arbor may be part of the Colt frame, the wedge isn't actually part of the Colt frame at all from a technical standpoint.
I think that it's only part of the design and not part of the frame.
So mykeal, maybe folks are indeed technically correct when they say that the Remington frame is stronger. The Colt frame won't stay together without a wedge which isn't even part of the frame at all.
All that the Remington needs to work is a cylinder pin which is what the definition about the differences of their frames boils to too.
The 2 piece Colt frame won't stay together without a wedge. The Remington won't work without a cylinder pin, but the Remington frame exists as a single unit while the Colt's doesn't without a 3rd party wedge.
So to criticize about how people supposedly misuse terms such as "stronger Remington top strap frame" and "Colt frame" can be criticized from both ends and different angles.
We shouldn't criticize people over semantics when we all know what they mean.
So which is the stronger design may not be based on the frame of either of them at all. It's the Colt wedge arbor system verses the Remington cylinder pin.
So what if most folks just like the simplicity and durability of the Remington better?
Why try to convince them otherwise or to correct their English when the Colt frame doesn't even have an aligned barrel attached to it?
It's a 2 (or 3) piece Colt verses a 1 (or 2) piece Remington depending on how one wants to define it. But not about a frame verses a frame, since of the two only the Remington has a solid unitary barreled frame.

For reference, here's a lot of previous threads about Colt arbors and the problems associated with them:

http://thefiringline.com/forums/showthread.php?t=357714&highlight=loose+arbor&page=2

http://thefiringline.com/forums/showthread.php?t=352233&highlight=loose+arbor

http://thefiringline.com/forums/showthread.php?t=355307&highlight=loose+arbor&page=2

http://thefiringline.com/forums/showthread.php?t=352233&highlight=loose+arbor

http://thefiringline.com/forums/showthread.php?t=395043&highlight=loose+arbor

http://thefiringline.com/forums/showthread.php?t=346504&highlight=loose+arbor

 

[breed]

i wounder how colt managed to keep the open top in production for some 30+ years. and i think they were still selling them darn near to the 1880's. it seems I've read of more then one old open top conversion being carried and shot well in to the 1920's. i wounder what old wild bill would have said if you told him he was carrying a inferior gun.....lol

 

[Delmar]

...i wounder what old wild bill would have said if you told him he was carrying a inferior gun.....lol

I don't know, but is it possible that the abor on the original Colts fit better than it does on some of the Italian repos?

 

[sundance44s]

So ..with all said and done ..I suppose if you welded the wedge in place on an open top Colt , it would be indeed as strong as a 1858 Remington .
But good luck when it comes time to clean it .
Of course you could peck the wedge in and tighten up the Colt between shots ...anyway ...range time with both will indeed show the truth of it .
It isn`t rocket science ..its so easy even a cave man could see the difference.

 

[zippy13]

So ..with all said and done ..I suppose if you welded the wedge in place on an open top Colt , it would be indeed as strong as a 1858 Remington .
Or, you'd just hasten a base pin/frame connection failure .

This afternoon I was shooting my Ruger OA and loaned my buddy a Remington replica. Have you ever have one of those naughty cap days?... when the caps think their role in life is not to just go pop, but to go pop and then run and hide where they can maximize their potential to jamb the works. I don't know how many times I had to pull the pin to free the wheel -- a year's worth in one afternoon. I was wishing the Ruger's pin was as easy to withdraw as the R1858's. Now Sundance44s is talking about a Colt with a welded wedge - - Yikes! How about we work on a way to just solder the wedge, that way we could un-solder it from time to time