craigc said:
Is that why N-frames shoot loose, because the frame is a "low stress part"?
The reasons that ANY revolver (S&W, Ruger, Korth, Freedom Arms, Colt, etc, etc) "shoots loose" are the same reasons that cause any mechanical device to wear out. Same reasons that require aircraft and spacecraft engines to be rebuilt after limited hours of operation. There is nothing magical about the mechanics of a revolver.
craigc said:
Is that why Freedom Arms uses a tougher alloy, 17-4 as opposed to Ruger's 415, for their CAST frames?
Freedom arms uses a tougher alloy because they are targeting a more limited market (higher price point) than Ruger. If 17-4 is necessary for revolver frames why doesn't Ruger use it? Here's a hint: It's not required for Ruger's market.
craigc said:
The cylinder contains the pressure but the frame withstands the backthrust in one direction and the bullet slamming into the forcing cone in the other.
You obviously don't know that the hoop stress component of pressure is MUCH more critical than the longitudinal effects in a pressure vessel.
Let's say we're running at 454 Casull pressures of 65,000 PSI. That means that the backthrust is 65,000 * .205 = 13,000 pounds, therefore the force of the bullet slamming into the forcing cone is approximately equal. Means that we have to take a total load of around 30K. Even something as crappy as cast 415 has a yield strength of around 50,000 PSI, while 17-4 is around 150,000 PSI and forged 4340 is around 200,000 PSI. What's the load distribution versus the size of the frame and yield stress of 415 or 17-4 or 4340? That'll tell you how many cycles the frame will withstand before it deforms a given amount. I would hope that your Freedom Arms that is probably 4 times the price of your Ruger offers at least some longevity benefit.
To look at what's required in cylinders and barrels, a Freedom Arms Model 83 in 454 Casull for example has a chamber diameter of about .478" and a cylinder wall thickness of about 1/8". You can plug the numbers in for yourself here
http://www.engineersedge.com/calculators/hoop-stress.htm and see why nobody uses a material with a 50,000 PSI yield strength in their 454 cylinders, but it's fine in a low-stress application like the frame.
craigc said:
We're not talking about airweight .38 J-frames that someone might put 500rds through in its lifetime. We have several reports of 329's shooting themselves apart way faster than any steel N-frame.
We're talking about revolver frames in general compared to the other components of the firearm. There is a reason that stronger materials are required in cylinders and barrels than frames.
craigc said:
Yes, S&W did aluminum cylinders for their early 10-shot .22 K-frames and similar J-frames.
How did that work out for them? There's a reason that they only used it in EARLY guns and not in any of their later models.
craigc said:
There are lots of aluminum barrels but they all have steel liners.
Why do you think they have STEEL liners?
200apples said:
45_auto, was it? attempted to compare an AR15 action to a revolver... but what he is forgetting is that in an AR, like an 870 (to offer just one additional example...), the bolt will lock to the barrel so there is less need for a stronger receiver... unlike a wheelgun where the frame must support the forces of recoil.
No, I didn't forget how an AR15 works. I was using it as an example to point out how some engineer (Eugene Stoner) had analyzed the forces reacted by his receiver and concluded that since it was a lower stressed component of the firearm that cheaper, weaker materials could be used in it's construction. Same thing applies to revolver frames compared to their other components which must resist the stresses of chamber pressure such as cylinders and barrels. The hoop stress component of the pressure in the cylinder (chamber) and barrel is the critical design factor. The lower stresses on the revolver frame (no hoop stress) allow the use of cheaper, weaker materials in a cast component.