I'm looking to have some reamers and dies made up for a magnum-length, rimmed .40 caliber straight-wall cartridge. Who's the best for this sort of thing? I was leaning towards Manson for the reamers. For the dies, Hornady seemed reasonably inexpensive and quick for the cost.

I've worked out the math and prepared minimum chamber and maximum cartridge drawings following the CIP format. Ideally, I should be able to turn these over to whomever is right for the job and they run with it.

Purpose is to take a six-shot 686 beyond the 646 to a .40 caliber magnum. Anyone so inclined could use this cartridge as the basis for a seven-shot 610.

I would go with Manson for the reamers. I have had them make me a few custom ones and they were perfect and cut like a dream.

Hornady, RCBS, or some of the upper level rifle die makers should all be able to do the dies.

Let us know how that turns out. I made 2 686s into 40 S&W with moonclips. I would like to know how they hold up to a 40 Magnum.

__________________
protocalldesign.com

I had been under the impression that an L-frame cylinder wasn’t “big enough” for .40/10mm and six shots, and that was the entire reason that the Model 646 used a titanium cylinder.

If this isn’t the case, could S&W have made the 646 with a stainless cylinder?

Also, I know of 10mm Magnum and I have heard of .40 Super, but I have never heard of .40 Magnum. What’s the back story on this round?

Both of my 686 40s have stainless cylinders. They are having no problems at all. I think if they made the 929s with SS cylinders, they wouldn't have had all the problems with them. I didn't make mine 10mm because I didn't know if the cylinder could contain the pressure, and didn't need it for a match/target gun anyway.

__________________
protocalldesign.com

Thanks, all. I'll give Manson et al a call tomorrow.

Re: titanium vs SS cylinder on the 646, the reason they used titanium was more for weight and "coolness" on the short run of 646 PCs. After that, they had a bunch of spare parts sitting around so they built the non-PCs using the titanium cylinders to consume remaining stock.

Re: where did 40 magnum come from, I made it up. I took the spec drawings for 41 magnum, 357 magnum, and 10mm and worked out the math for a .40 caliber magnum. For all you who as kids asked "when is trigonometry actually going to help me in real life," this is the day.

Several folks have had SS cylinders made for their 646's in 10mm. Invariably, the gunsmiths have told them to only use lower power 10mm loads (e.g. silvertips). Generally, my impression is that the concern was the thickness of the cylinder wall at the cylinder stop notch. Everywhere else, sufficient material was presumed.

I intend to address this concern in three ways and be able to run this cartridge at full magnum pressures. First, reamers for traditional autoloading cartridges (e.g. 10mm/40s&w) provide for much more generous openings in the chamber mouth to accommodate smooth, reliable feeding (generally +0.004" or more). Reamers for revolvers are typically much more conservative (generally 0.002"). Second, 10mm/40s&w are slightly tapered, this will be a true straight-wall cartridge. Per SAAMI, the minimum chamber mouth width for 10mm is 0.4291", mine will spec at 0.425". So, I'm expecting at least 0.004" more of material, without taking into account the fact that this will be a one-off and presumably closer to the actual spec than what mass production allows. Not a lot, but something. Third, I'm resizing 41mag brass, so the brass directly beneath the cylinder stop notch will be significantly thicker and more robust than 10mm/40s&w at the critical point.

Worst case scenario, I can run it at lower pressure but still exceed muzzle energy of hot 10mm loads, if not 357 magnum, due to larger case capacity.

Well it sounds very interesting, but it’s viability is far beyond my pay grade. How will it compare to 10mm Magnum?

It should be on a par with 10mm magnum.