M92 stainless 357mag barrel

The Rossi Model R92, a lightweight carbine for Cowboy Action, hunting, or plinking! Includes Rossi manufactured Interarms, Navy Arms, and Puma trade names.
Reese-Mo
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Re: M92 stainless 357mag barrel

Post by Reese-Mo »

Jeeze. The guy in that thread was wingin' it at best.
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Re: M92 stainless 357mag barrel

Post by Archer »

Reese-Mo wrote:As for a total rebarrel - which is probably the way to go - I would not put money on threads that are hard to cut. Trust me, I've done it, they are ALL hard to cut. But, thread pitch is determined by what is available on the lathe. Don't ask a lathe to cut 21.6 threads per inch. They don't do that. Same with metric geared lathes. They do the standard thread pitch spacing in whole and fractions of millimeters, based on quarter millimeter steps in smaller pitch and half in larger pitch. Braz/Rossi has to use an industry standard pitch, to do otherwise would be too expensive and useless. As for the wacky diameter, they are ALL wacky. The pitch is more or less ok, thread major diameter... you gotta have the old barrel to check that. Next is the thread profile, which could be 60 or 50 or some other odd angle. That's just a matter of grinding the cutter to the angle that is needed.
Reese-Mo wrote:Jeeze. The guy in that thread was wingin' it at best.
Yeah that was the example I was thinking about as well.

As an engineer who works prototype aircraft programs, I have some experience trying to get obsolete parts, new parts that mate to obsolete parts and special order items. I've also got some experience with what we get back from the machinist even when we are asking for something 'simple' or 'normal'.

We often provide the CAD or even the CAM files necessary for a computer driven mill to do the work.
SOMETIMES the machinist decided the part is 'simple' enough that they want to run it on a manual mill.
A nicely bead blasted satin finished part is a good indication that the machinist decided to beat the machining mismatches into oblivion.

When a stainless steel part shows up with a discrepancy report that says the eddy current machine was turned up too high and 'melted' the end of the part there's a good chance somebody dropped it and when they smoothed off the effects of a 10 lb part coming down on a eighth of an inch edge it came up short.

Alexander Arms has picked non-standard threads on purpose. They MIGHT be threads that can be cut on a standard lathe but they are threads that NOBODY has used even in the firearms industry for anything the last 20 or 40 years.

Essentially we standardized thread forms and pitches across a few decades from WWI through the 50s or so.
Spar parts among the allies in WWI weren't standard. It was better but still a mess in WWII. Those were major drivers in the fastener size industry.

It isn't smart to pick oddball thread forms but it isn't as unusual as it should be.
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Re: M92 stainless 357mag barrel

Post by Reese-Mo »

Arch, I agree but..... I dunno, some of the weirdest thread pitches in the universe tend to be in the firearms industry. Remember when B-Square was in business, and all the oddball tap/die sizes they had? They had stuff like 8-32, 8-36... then 8-40, 8-44, 8-48, stuff that's just not really used outside of guns at all.

IF the barrel pitch was 1mm, that's awful fine for such a large diameter thread. I'd not have guessed that at all. I would have guessed something more like 1.5mm to 2mm

On the other hands foot - cutting a thread pitch that fine, you do in in one take. The major/minor diameter should be something just over .6mm, which is easily doable in one pass.... so I don't have any clue as to the issues the guy in the old thread was having, except, he was wingin' it. And damn right I'd do it on scrap three or four times before I did it on a barrel, because I dont (or didn't) do it maybe five times in damn near 20 years. But a guy who fits barrels, really should have no issues.
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Re: M92 stainless 357mag barrel

Post by Archer »

Those threads you complain about with regards to B-Square are still all over the optics part of the firearm industry.

"And damn right I'd do it on scrap three or four times before I did it on a barrel..."

Absolutely the way to go when you are doing something new, strange or odd. Use every advantage you can get.
I've had mechanics misalign parts by up to 30 degrees on an airplane and I'm still shaking my head over how in the heck it happened. (Had an engineer mess up the markings on a part so that 'FWD' and 'AFT' weren't and it got installed in the assembly backwards before the assembly went on an airplane.) Transparencies, paper or plastic mock ups, pilot holes, dry fitting and spare parts where available and affordable can save a project from dying of a mistake.
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