GP100 in 45 colt

[mcb]

For fun with the morning's tea...



A hypothetical revolver cylinder. 1.550 inches in diameter and 1.610 inches long. Five 45 Colt chambers cut in it at maximum tolerance per SAAMI specs to make the resulting chamber walls as thin possible. The bolt hole circle was my best guess from looking at pictures, at .950 inches. This resulted in .065 inch walls between chambers and .055 between the chamber and OD. A simplified 45 Colt Case (no primer pocket or flash hole) was placed in one chamber. The cylinder was modeled as carbon steel 4140 quenched and tempered to HRC30. A static Finite Element Model run with 14,000 psi pressure applied to the inside surface of the brass cartridge. The peak resulting von Mises stress is ~67 ksi. The yield strength for this heat treatment of 4140 is ~116 ksi so we are at 58% of its yield strength. Deformation in the above model is plotted at nearly 200 times normal. Maximum deflection at any point in the model was less than .001 inch.

For comparison. I measured my S&W 625 and it has a wall thickness between chambers of ~.072 inch and chamber to OD of ~.070 inch and it will safely shoot 45 ACP +P at 23,000 psi.

I would be happy to update the model with more accurate dimensions or material properties if someone has some info to share. The bolt hole circle dimension from a 44 Special would be awesome. I used 4140 as it is commonly used in firearms but I have no idea what Ruger uses in their blued guns.

 

[<*(((><]

@mcb Thanks for the model, that's interesting to see. Hopefully, someone with a 44 Special will get your the bolt hole circle.

Coming from a pretty ignorant knowledge of metallurgy as it relates to pressures (myself), is there a linear correlation in cylinder wall thickness and pressures?

Meaning the % difference between your S&W 625 compared to your hypothetical revolver cylinder of 10% of chamber wall dimension and 21.5% chamber to OD; does it correlate linearly with the difference in pressures between 45 ACP +P and 45LC (23,000 psi vs 14,000 psi) of 39.2%. Meaning all other things being equal between the two cylinders metallurgy wise, does the fact that both dimensions of the chamber wall dimension and chamber to OD is less than the 39.2% difference in pressure will that correlate linearly with it being safe, or does it not work that way?

Hope my question is clear enough, it would be interesting to know just for my head scratching.

 

[CraigC]

The .44Spl GP has an outer chamber wall thickness of 0.062".

None of which addresses the already very thin forcing cone.

 

[DPris]

Or, we could just simplify it & say there isn't enough room in the existing GP for a .45 caliber version, Ruger isn't going to push the existing envelope to make one, Ruger isn't going to create a special version of the GP with frame modifications to make it practical, and Ruger just flat is not going to build a .45-caliber GP.
Denis

 

[strangelittleman]

Why do so many want a 5-shot .45 LC GP100? I don't understand the attraction.

 

[mcb]

@mcb Thanks for the model, that's interesting to see. Hopefully, someone with a 44 Special will get your the bolt hole circle.

Coming from a pretty ignorant knowledge of metallurgy as it relates to pressures (myself), is there a linear correlation in cylinder wall thickness and pressures?

Meaning the % difference between your S&W 625 compared to your hypothetical revolver cylinder of 10% of chamber wall dimension and 21.5% chamber to OD; does it correlate linearly with the difference in pressures between 45 ACP +P and 45LC (23,000 psi vs 14,000 psi) of 39.2%. Meaning all other things being equal between the two cylinders metallurgy wise, does the fact that both dimensions of the chamber wall dimension and chamber to OD is less than the 39.2% difference in pressure will that correlate linearly with it being safe, or does it not work that way?

Hope my question is clear enough, it would be interesting to know just for my head scratching.

If you make the thin wall pressure vessel assumptions (not bad approximation for the outside weakest part of a revolvers chamber) then yes it scales linearly with pressure and linearly with wall thickness . Double the pressure double the hoop stress in the wall. Double the wall thickness you cut the stress in half. In reality given the geometry involved in this problem that is probably correct enough just for a first approximation.

The .44Spl GP has an outer chamber wall thickness of 0.062".

None of which addresses the already very thin forcing cone.

In the vain of making this a worst case, I assume the .062 wall thickness of the 44 Special is measured on a minimum spec chamber diameter for 44 Special. That make the calculated bolt hole circle the largest possible with current known dimensions. The result is a .969 inch diameter circle (.019 larger than my earlier estimate) When I put that dimension into my earlier model the chamber to OD wall gets pretty thin. .0455 while the wall between chambers goes up to .079. I re-ran the FEA with this updated geometry and we get a new peak stress of 79 ksi or about 68% of our assumed 4140 steel's yield strength. That is getting a bit sketchy, but the static model I am using and all the dimensions and assumptions I have used so far are to create a worst case analysis. Still seems plausible, but admittedly difficult.

The forcing cone/barrel shank issue may very well be the deal breaker. Not too worried about raw barrel pressure as the frame is pretty beefy around the thin shank and the pressure is dropping fast by the time we get there but breaking the shank off do to other dynamic forces generated by the bullet's travel down the bore and recoil dynamics could make failure a real possibility. Though the frame is probably big enough to allow for a slightly larger barrel shank to be used without compromising the over build frame. That analysis cannot be approximated with a static FEA analysis.

Or, we could just simplify it & say there isn't enough room in the existing GP for a .45 caliber version, Ruger isn't going to push the existing envelope to make one, Ruger isn't going to create a special version of the GP with frame modifications to make it practical, and Ruger just flat is not going to build a .45-caliber GP.
Denis

Agreed, Ruger ain't making one, but that makes for boring discussion. Any maybe, just maybe a third party will pick up the torch...

 

[ATLDave]

I'm no engineer, but I doubt any manufacturer would put out a firearm that was 68% of the way to failure on every shot.

Does anyone know what pressure the SAAMI 45 Colt proof load is?

ETA: Page 181 of this document appears, to my untrained eye, to suggest that the proof load for a 14,500 PSI 45 Colt round would be ~21,000 PSI.

 

[ray15]

I'm no engineer, but I doubt any manufacturer would put out a firearm that was 68% of the way to failure on every shot.

Did you see the picture of the Taurus Judge cylinder posted in this thread?

 

[ATLDave]

I'm not counting things you find at the bottom of a Cracker Jacks box.

 

[ray15]

Even if you are making Cracker Jack, you are a manufacturer.

 

[ATLDave]

I cannot argue with that.

 

[mcb]

LOL, yeah trying to use a Taurus Judge to support my side of the discussion was probably not the strongest of supports...

 

[mcb]

I'm no engineer, but I doubt any manufacturer would put out a firearm that was 68% of the way to failure on every shot.

Does anyone know what pressure the SAAMI 45 Colt proof load is?

ETA: Page 181 of this document appears, to my untrained eye, to suggest that the proof load for a 14,500 PSI 45 Colt round would be ~21,000 PSI.

Running 21,000 psi proof pressure in my model puts us at 118 ksi or 101% of yield strength. Going to need to use something better than 4140 HRC 30. But 4140 is far from a high end alloy. Simply stepping up to 4340 we can get to 160ksi yield strength from a similar heat treatment with only a modest cost increase (dreams should be affordable too). Now even at proof pressures we would only be ~73% of yield.

 

[CraigC]

Or, we could just simplify it & say there isn't enough room in the existing GP for a .45 caliber version, Ruger isn't going to push the existing envelope to make one, Ruger isn't going to create a special version of the GP with frame modifications to make it practical, and Ruger just flat is not going to build a .45-caliber GP.
Denis

Exactly!

Agreed, Ruger ain't making one, but that makes for boring discussion. Any maybe, just maybe a third party will pick up the torch...

To what end? Personally, I've had many discussions with custom gunsmiths on what is and isn't possible, exploring all the possibilities in building a custom gun but don't enjoy spending much effort discussing something that will never be any more than academic (mental masturbation).

The third parties have already decided that there isn't enough room.

Simply stepping up to 4340 we can get to 160ksi yield strength from a similar heat treatment with only a modest cost increase (dreams should be affordable too).

I'm all about making dreams come true and have several custom guns in mind that may seem silly to some but there comes a point where you have to decide that the costs and effort cannot be justified when something more useful is already available.

 

[MTNSTRYDER]

Why do so many want a 5-shot .45 LC GP100? I don't understand the attraction.

The 45LC is more versatile than most other rounds and if you roll your own it can do more than 44 or 357 ,load your own shot shells,light,heavy,fast,slow the 45LC does it all.
To Rugar PLEASE MAKE THIS GUN!

 

[DPris]

Not listening, huh?
Neither Rugar nor Ruger will make one.
Denis

 

[cfullgraf]

I'm a big fan of the 45 Colt cartridge but I really do not expect to find it produced in a Ruger GP100 or S&W L-frame.

There is a tread on the "High Road" from back in 2014 concerning making the S&W M69 in 45 Colt and it basically said that it was not reasonably possible. rcmodel said it would not work and I trust his knowledge, experience and judgement.

I agree that the same could be applied to the GP100.

In my opinion, it is time to move on.

P.S. I enjoy shooting my Ruger GP100 44 Special and S&W M69 44 Magnum. Since I reload, it really does not matter whether I reload 44 Special or 45 Colt.

 

[murf]

looks like the barrel is thin enough on the 44 special:

a .023" increase in that barrel diameter doesn't look practical.

murf

 

[CraigC]

The 45LC is more versatile than most other rounds and if you roll your own it can do more than 44 or 357 ,load your own shot shells,light,heavy,fast,slow the 45LC does it all.
To Rugar PLEASE MAKE THIS GUN!

Pure nonsense. The .45Colt is not more versatile in any platform and in this platform, it would be LESS capable. Try reading the thread.

 

[Panzerschwein]

Or, we could just simplify it & say there isn't enough room in the existing GP for a .45 caliber version, Ruger isn't going to push the existing envelope to make one, Ruger isn't going to create a special version of the GP with frame modifications to make it practical, and Ruger just flat is not going to build a .45-caliber GP.
Denis

And the .44 special can do anything a .45 Colt can, especially when you exclude magnum.45 Colts that a .45 GP would not be use able in.

 

[mcb]

And the .44 special can do anything a .45 Colt can, especially when you exclude magnum.45 Colts that a .45 GP would not be use able in.

We could do a magnum 45 Colt GP100 (ie "Ruger Only" loads) If you don't mind spending a little money. Make the cylinder from a martensitic alloy steel like Aermet or similar. Yield strengths over 300 ksi are possible along with high hardness in the HRC50's without becoming brittle. You could run up to 40,000+ psi chamber pressures safely with that material. Bump the barrel shank up 1/32 -inch in diameter to address that issue. If you really want to push it bump the barrel and firing pin down in the frame .020-.025 inch and we could really crank the Ruger Only loads. Probably not profitably or good for your wrist...

 

[Panzerschwein]

We could do a magnum 45 Colt GP100 (ie "Ruger Only" loads) If you don't mind spending a little money. Make the cylinder from a martensitic alloy steel like Aermet or similar. Yield strengths over 300 ksi are possible along with high hardness in the HRC50's without becoming brittle. You could run up to 40,000+ psi chamber pressures safely with that material. Bump the barrel shank up 1/32 -inch in diameter to address that issue. If you really want to push it bump the barrel and firing pin down in the frame .020-.025 inch and we could really crank the Ruger Only loads. Probably not profitably or good for your wrist...

Ha! Very cool.

I wish someone could make something along the size and weight of the Charter Bulldog, but more durable for a lot of shooting. The one I had went out of time quickly, among other issues. Something like the Rossi 720 would be nice, I can't seem to find any of those for sale.

 

[DPris]

The forcing cone is a primary no-go on such a gun.

And as I've said- Ruger is not going to alter the frame just for a limited-interest .45 Colt GP market.
Denis

 

[wildcatter109]

As CraigC has been trying to point out, it is reality that Ruger will never do this, and the the three gunsmiths he mentioned also will never touch it, I too talked to Bowen and after being told no to any GP-100 conversion, was also told by Clements who has done some GP-100's in the past, that there is now way to safely do a 45 Colt conversion to any altered GP-100 frame that would even be safe for the lightest cowboy loads used in the SAA Colt. This is a wasted conversation. The only way you could ever do it, is to do it yourself, if you really wanted to blow one up go for it! As you know, many do even more needles acts that are dangerous to others besides themselves.

 

[mcb]

And yet Taurus has managed to get 5rds of 45 Colt into a revolver with a cylinder that is ~.020 inch smaller in diameter than a GP100.

Not sure I understand the sentiment of some in this thread to stifle the conversation by simply quoting some "expert" that says its not possible in an attempt to thread cap. I thought the point of a forum was to discuss things...

“Science is the Belief in the Ignorance of Experts” — Richard Feynman.

Asking a gun smiths if it is possible to make a 45 Colt GP100 is sort of like asking the local mechanic to design a new engine for your car. Sure he might be able to drop that 500hp V-8 crate engine into your V-6 Camaro but if you ask him to redesign that engine to lighten it by 30% without a loss of HP you have sort of step outside of his expertise. It might actually take some real engineering and some R&D to make a GP100 in 45 Colt to work rather than just a gun smith mismatching and/or modifying parts.