Why cowboy cartridges for cartridge conversion

The primary limitation is frame strength. The old cap and ball revolver designs, especially those with no top-strap, are significantly weaker than modern single or double action revolver frames with solid top strap. So these conversion guns cannot take the forces from loads producing pressures greater than traditional (SAAMI Spec) 45 Colt loads. The cylinder may also be a limiting consideration since the wall thickness of those conversion cylinders can be pretty thin.

The warning is because it is fairly common to load 45 Colt well above SAAMI Max Pressure for 45 Colt since most modern 45 Colt revolvers can easily handle the force associated with this greater operating pressure. A conversion revolver cannot in most cases hence the warning to use 45 Colt that more close replicates the traditional loadings. Hope that helps.

Londez, the primary limitation is the cylinder. You mention the Remington and the conversion cyls for the Rem. pattern that have a removable cap or "drop cyls" (containing an individual firing pin for each chamber) may be limited slightly because they have less contact/ support from the recoil shield. That is important because the cyl cap becomes the breech face. The conversions that use a conversion ring have better support because the ring is the breech face and has full contact with the recoil shield. Either system is period correct for the Remington.
The open top Colt pattern didn't use the "drop cyl" type conversion but they are offered today. Likewise, the conversion ring setup for the open top offers the same full support for the cyl.
Both of these platforms are plenty strong enough for the conversion cyls they support. The fps limitations are put there for manufacturers protection and I believe one manufacture still lists 1000 fps. I'm pretty sure that no 1st tier factory ammo (lead bullet) exceeds 1000 fps.

Contrary to popular belief, the the open top design is considerably stronger than the perimeter frame or top strap design. I actually bent a Remington frame while loading an oversized ball. You'll shear a lever screw on an open top before you pull the arbor doing the same thing. That's not my "proof" of strength by the way, it's just two personal incidents that happened to me.

Mike

Before any conversion the guns were intended for use with black powder. And the black powder generates a longer smoother pressure build. So it's less of a shock to the metal. And since these are copies of the originals and generally made to a lower price point they are made to do fine with the lower pressure and not much more. So what they are asking is that you don't load to exceed that limit. And that means up to and no more than around 850 fps and a lower pressure according to those makers that specify that limit.

Get a chance to shoot a BP gun be it cap and ball or black powder cartridge and you'll instantly feel what I'm talking about. It's more of a THUMP than a CRACK!

londez said:

Thankyou gentlemen. Very informative! Does anyone know why the bullets have to be unjacketed?

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A lead bullet will, in general, generate a lower peak pressure compared to jacketed bullet of the same weight pushed to the same velocity. This is in part due to it being easier to engrave the lead bullet into the riflings. The lower peak pressure is good and the lower engrave force is also good as this will reduce the stress on the frame as the pressure drives the bullet into the forcing cone and into the riflings.

Bore wear is another issue with jacketed bullets. The original black powder revolver barrels and modern copies are made from relatively mild alloys which work fine for lead bullets but wear quickly with a steady diet of jacketed.

Not sure I buy the wear issue. Copper or brass on steel has a significantly lower coefficient of friction than lead on steel. Hence the need to lubricate lead bullets but not jacketed bullets. Both lead and copper/brass are significantly softer than even mild steel let alone the medium carbon steels common in gun barrels.

Friction coefficient has nothing to do with the greater force required to engrave the harder alloy into the rifling and the resistance (and wear) it provides once engraved. Just push two bullets down a bore, a lead one and a jacketed one, and see which provides greater resistance.

45 Dragoon said:

Contrary to popular belief, the the open top design is considerably stronger than the perimeter frame or top strap design. I actually bent a Remington frame while loading an oversized ball.

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Mike, the bottom part of the frame has (almost) nothing to do with the top one - those are two separate issues. On a cartridge revolver you have a cylinder that is violently slapping the frame forward as the bullet accelerates in it AND (bullet) hitting the forcing cone as it engraves into the rifling. Compare that to a cap & ball design, where the bullet only engraves the rifling while the cylinder is forced to the back - the first applies much greater force. On a modern revolver frame stretching always manifests itself at the top of the frame, never at the bottom part. This is the sole reason why Colt went with the top strap design on the 1873 revolver - open strap design would simply not hold the beating of the quite portent .45 Colt. Now, I'm not saying that I don't like open tops (I love them!) and I don't say that they are inferior - they are a great design if only used as originally intended, i.e. as a Cap & Ball revolver.

Mizar said:

Friction coefficient has nothing to do with the greater force required to engrave the harder alloy into the rifling and the resistance (and wear) it provides once engraved. Just push two bullets down a bore, a lead one and a jacketed one, and see which provides greater resistance.

Mike, the bottom part of the frame has (almost) nothing to do with the top one - those are two separate issues. On a cartridge revolver you have a cylinder that is violently slapping the frame forward as the bullet accelerates in it AND (bullet) hitting the forcing cone as it engraves into the rifling. Compare that to a cap & ball design, where the bullet only engraves the rifling while the cylinder is forced to the back - the first applies much greater force. On a modern revolver frame stretching always manifests itself at the top of the frame, never at the bottom part. This is the sole reason why Colt went with the top strap design on the 1873 revolver - open strap design would simply not hold the beating of the quite portent .45 Colt. Now, I'm not saying that I don't like open tops (I love them!) and I don't say that they are inferior - they are a great design if only used as originally intended, i.e. as a Cap & Ball revolver.

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Still not buying it. The gun barrel even and old cap and ball revolver is still much much harder than a jacketed bullets. Medium carbon steel typical used for gun barrels is Brinell hardness of 250-300 maybe a touch higher with modern steels. Copper is 40-50, even Brass is only ~100. Lead is usually in the 10-30 range Erosion form hot propellant gases is going to be far harder and wear faster on barrels than the bullet is.

mcb, have you seen a hardened steel shaft eaten away by the oil seal? It's pretty much the same here.

Mizar, I appreciate your words but it seems that most folks tend to forget that the arbor IS the "top strap" "stand in" for the Colt open top. The top strap framed S.A. creates a taller window (bigger equals weaker) in the frame to contain the cylinder. The arbor on the other hand is rather thick which is where it's tensile strength is. It is only half the distance from the base of the frame and is supported extremely well at both ends creating a rather short (short = compact= strong )"half-window" if you will. Even though the the barrel is attached with a wedge, the wedge is (should be) under tension which keeps all clearances closed while assembled (this encompasses the arbor length correction et al.). Loose wedges allow the open top to destroy itself. This is especially true for cartridge open tops firing smokless rounds ( which is what lead me to what I do now for a living). This is just a short explanation of a fairly deep topic of comparing the two differing platforms. Before I forget, you may notice that "solid" wedges (with just a cutout for the screw head clearance) is used on the cartridge conversions and the '71 Open Top instead of the almost cut in half wedges to allow room for the spring . . . stronger wedges tend to work better/last longer.
I'm definitely not saying open tops are "King of the hill" by any means but they are quite substantial when all things are set up correctly. The engineering is there (archaic as it may be!).

My belief is that economics is why Colt went to the top strap. Not to mention a much more compact revolver. An open top is much harder (expensive) to produce CORRECTLY than a top strap frame. And besides, Sam wasn't around to say no !!

Mike

It occurs to me that when Uberti makes a cap and ball revolver, it is proofed under Italian rules for a muzzleloader.
When they make a finished gun in the configuration of a cartridge "conversion" it is proofed for the specs of that cartridge; there is no CIP standard for "cowboy" ammunition.
I guess the question is, are their C&Bs overbuilt so they can use the same parts for cartridge equivalents?
The aftermarket cylinder vendors are obviously playing it safe.

The matter of "pressure curves" smokeless vs black is an interesting point. Have you ever seen a pressure curve of FFFg vs Bullseye? I haven't. There has been some work for Damascus shotguns, showing smokeless loads that do not exceed black powder pressure peak or rise time.

It may be like cast bullets in Glocks... "Don't do it" vs "I do it all the time."

londez,
Shooting smokless rounds out of a true blackpowder era revolver is an issue for those "in the know". And, I'm not all that sure the " those that know" know all they need to know!! Lol!!

First of all, the current frames from the Italian reproductions are excellent support systems for the conversion cyls made for the specific revolver. The main "piece" in the puzzle is the cylinder which has been designed to "do what it does". You should have zero worries if you stay within the stated limits from whichever manufacturer you choose.

Here's a little something for you and others to think about. The material in a cartridge cylinder is thinest at the rear and thickest at the front. Likewise, the material in a cap &ball cyl is thinest at the front and thicker at the rear. So, generally speaking, if one were to have a cylinder failure . . . I would submit that a cap & ball cylinder would be more dangerous (tearing front to back) than a cartridge cylinder (tearing back to front). It's a thinker . . . .

Mike

kinda gives a different spin on those "dangerous" open tops . . .

mcb said:

Still not buying it. The gun barrel even and old cap and ball revolver is still much much harder than a jacketed bullets. Medium carbon steel typical used for gun barrels is Brinell hardness of 250-300 maybe a touch higher with modern steels. Copper is 40-50, even Brass is only ~100. Lead is usually in the 10-30 range Erosion form hot propellant gases is going to be far harder and wear faster on barrels than the bullet is.

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Lead bullets need lubrication not because of potential bore wear but to prevent them from leaving large parts of themselves down the barrel due to friction. The melting point of lead is very low compared to copper or brass alloys and will easily be exceeded at high velocity or pressures which causes leading. Gas cutting of too hard a lead alloy also causes leading but will normally happen in the first few inches of barrel while running out of lube will lead the last part.

Ian McCollum is a nice guy with plenty of (historical) knowledge. With that said he is actually quite, let's call it "unfamiliar" and leave it, with the technical aspects of firearms operation, firing mechanisms, action timing and etc. When one is shooting an old revolver with "not-up-to-the-modern-standards" strength he should adjust his load and powder of choice accordingly. Frames are stretching because of Mr. Newton's third law, not by peak pressure itself. People are simply concerned by the fact, that shooting a vintage revolver with unsuitable smokeless powder that CAN bring higher peak pressure for achieving the same velocity as a black powder load can rupture the cylinder, not to stretch the frame.