Barrel Thickness/Outside Diamter

[barnbwt]

Hello, once again!
I'm working on a .357magnum pistol platform design, and I'm having some trouble figuring out what to use (as a starting point) for my barrel dimensions. Running the figures, less than 1/10th of an inch is actually necessary to contain .357 pressures (see the chamber web thickness of an 8-shot 327 if you don't believe me), but actual barrel thicknesses are much greater. I assume the barrel thickness is mostly defined by bending/buckling stress, raising harmonic frequencies, reducing barrel-whip, and providing a big enough interface with the frame. For some reason, there is a dearth of these details online, as far as I can tell.

My only () .357 is a TRR8 with a gigantic aluminum shroud, so I can't really take numbers from it with calipers. Would some of you find gents mind posting up the outside diameter of some (your?) magnums? If possible, I'd like to use an existing barrel and cylinder (the most "failure critical" items in a revolver, I will leave them to more qualified designers) of a common maker for my prototype (not building it, yet, Mr. BATFE, just thinking ahead...).

I am most interested in the usual suspects' "pencil-barrel" diameters;
S&W N-frames (and maybe L-frames)
Ruger Blackhawk (new or old)
Ruger Redhawk (I will assume >>Blackhawk diameter)
Taurus Large-frame (sorry, I don't know my Tauri models well. Their barrels are fine, even if some find the actions questionable)
Colt .357's (sorry, I'm not up on my Colt model names, either)

For extra credit (), I could also use the cylinder outside diameter and outer wall thicknesses. For now, though, I'm basing my design around the TRR8 cylinder. So long as my frame design is stronger than the cylinder/barrel allowables, it shouldn't fail first.

I've not looked into it much, because it's more complicated, but I might try to implement a Dan Wesson-style shroud attachment, or even a S&W two-piece barrel setup. Anyone know how thick those (thinner) barrels are?

And finally, aw, what the heck...What's your favorite method for attaching a barrel to a revolver, and why? DW, crush-thread, thread-shimmed, pressed/pinned, tensioned, welded eek or other?

TCB

**I guess I'll assume .750" outside diameter, for now; I've seen at least a couple Ruger blanks going for that. I would much rather base the design around and off-the-rack replacement barrel, though.

 

[barnbwt]

C'mon, surely someone has a pair of calipers...

TCB

 

[dfariswheel]

I don't have a Dan Wesson to measure, but a neighbor has a thin barrel S&W .357 with a barrel 0.673 thick.

Like accuracy rifles the best method of installing a barrel is to torque in a threaded barrel.
The Dan Wesson system may offer better accuracy due to the tensioning effect of the threaded barrel.
Pinning is unnecessary and something Colt never did, although Colt's were on the average more accurate then the S&W.

 

[rcmodel]

The barrel doesn't need to be any stronger then the barrel shank threads & forcing cone.
The barrel shank, where it screws through the frame, is the thinnest part of the barrel, and takes the highest pressure & bullet impact of any other point on the barrel.
But you do need a shoulder, or thicker barrel, or a flange in front of the barrel shank so it can be tightened against the frame with the front sight on top.

On a .357 Mag:
S&W K-Frame = .507" - .542".
Colt New Service = .605" - .695".
Colt SAA = .615" - .695".
Ruger Blackhawk = 627" shank - .685" threads.
S&W N-Frame = .631" - .668".

rc

 

[barnbwt]

^^^Thanks for the info, RC, very thorough. That'll help my design estimations a great deal. Seems like the average is a tad over .600", so I'll base my strength calculations and frame design on that (for the time being), until I have a barrel in-hand. Once I've gotten my first-pass design worked up, I'll try to post a concept rendering, or something.

Like accuracy rifles the best method of installing a barrel is to torque in a threaded barrel.
The Dan Wesson system may offer better accuracy due to the tensioning effect of the threaded barrel.
Pinning is unnecessary and something Colt never did, although Colt's were on the average more accurate then the S&W.

I still haven't quite settled on which attachment method I like. The thread-on seems the simplest route, but I need to learn a bit more about the Dan Wesson and S&W barrel assembly setups to see if they offer any adavantages for my particular design.

As RC said, the forcing cone area of the barrel and socket are very high stress areas; have the cut threads been known to initiate cracking for failure in this area? Or are the threads cut with a radius in the groove instead of a corner? The lack of crack formation sites is the only benefit I could come up with (besides cost) for a pressed-in type attachment.

Thanks,
TCB

 

[barnbwt]

Okay, I've read up on Dan Wesson and S&W 2-piece barrel attachments--

Is there any difference between them at all? The S&W is done permanently, but the principal apart from that is the same, right?

Because my frame design is a break-top, I'm thinking about a tube/shroud arrangement, with a slight change; Simply have a shoulder at the forcing cone end of the barrel tensioned against a barrel nut at the muzzle. Because the frame breaks open, the barrel can be slid through muzzle-first, eliminating the need for threading near the forcing cone/frame interface. The shoulder would be conical to make it self centering. I'd need to run the figures to see if such an arrangement is actually stronger, though (since the bearing surface of the threads is probably bigger than the shoulder I've described).

For the current design, though, I'll constrain myself to a thread-in Blackhawk barrel for simplicity. RC, you don't happen to know the shoulder (widest) diameter of the Blackhawk, do you?

Thanks again,
TCB

 

[rcmodel]

.750" shoulder ahead of the threads according to my book.

rc