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Can I rechamber 586 cylinder for 646?


ltdmstr
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I have a SW 646 which is a 6-shot .40 SW revolver on an L frame. The 646 has a titanium cylinder, which is not real good at ejecting spent cases. I'd like to replace the titanium cylinder with a stainless cylinder. Since SW never made such a part, I was thinking I could take a stainless 586 cylinder that's .38/.357 and rechamber it to .40 SW and drop it in. Seems pretty straightfoward. But something tells me it can't be that easy.

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Toolguy, Hopalong and others will have more insight. You are looking at opening up the cylinder by 0.044 of an inch. 0.022 on each side. That is not much meat to take out but where I would be cautious is at the notches. They are directly in the middle of each chamber, making this point the weak spot on the cylinder. Other than that I don't see where anything else would be a problem.YMMV later rdd

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I have a SW 646 which is a 6-shot .40 SW revolver on an L frame. The 646 has a titanium cylinder, which is not real good at ejecting spent cases. I'd like to replace the titanium cylinder with a stainless cylinder. Since SW never made such a part, I was thinking I could take a stainless 586 cylinder that's .38/.357 and rechamber it to .40 SW and drop it in. Seems pretty straightfoward. But something tells me it can't be that easy.

PM Toolguy at Protocol Design, he is a vendor here.

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Opening up the cylinder by 0.044 of an inch. 0.022 on each side. That is not much meat to take out but where I would be cautious is at the notches. They are directly in the middle of each chamber, making this point the weak spot on the cylinder.

Better to work on titanium chambers finish OR ammo load!

I have no problem at ejecting spent cases (Major PF, 217g bullet) even in long (32 rounds) courses.

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Most smiths who do caliber conversions won't modify an L-frame 686 cylinder for .40 because the walls are too thin.

Has anyone done any destructive testing on a cylinder to find out whether they will actually take the pressure?

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I have shot a couple of boxes of factory ammo through my modified cylinder with no problems. I don't know how it would do with a steady diet of major. I suspect it would be fine since it was originally ok for .357 magnum, but can't say for absolutely sure.

Edit - Looking through the loading manual for .40 S&W, the loads to make major with 180 or 200 gr. bullets are running about 5,000 psi less than max for a .357 mag.

Edited by Toolguy
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Clements Custom does full house 10mm conversions on GP100s. I can't imagine that the L frame cylinder which is essentially identical in size to the GP100 would handle 40 S&W. But the GP100's notch is off center a nice bit too and that helps alot.

But aren't the stop notches the same on the 646 as a 686? If so the 646's TI cylinder would be weaker than the same one in steel. If it were me and it almost was until I decided to hold off on converting my L frame, I would hunt up a 586 cylinder and have it bored to tight SAAMI spec. The alloyed carbon steels like 4140 which is pretty much the gold standard gun making steel GENERALLY has a higher strength than 400 series stainless. If we knew what steels and heat treat S&W used on their cylinders we could know for sure how far it would go. Even heat treated TI alloy isn't a strong as most heat treated steels.

Edited by Shadowrider
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Then you end up with an L-frame version of the 610! Seems like you're going the opposite direction that most folks go when they get the titanium cylinder for the 625 - reducing mass instead of increasing it. I had a 610 and bought the 646. A world of difference between the two. The biggest one was the cylinder on the 610 - reminded me of a flywheel on an old hay baler. The 646 was more responsive to handle and shoot. If Smith had a replacement cylinder I'd still have my 646 :angry2:

Have you tried polishing the chambers?

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I have not polished the chambers b/c I was trying to avoid modifying the stock cylinder. But looks like that's the first thing to try. I had a 610, but the N frame was just massive. Not sure the extra cylinder weight will be a big deal on the smaller frame. At least not for me.

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I think you're going to find that polishing the cylinder, along with careful load selection, will be the practical answer to your problem.

Hopalong is the guy who has the scoop on this, but I know he's been working on the road a lot lately. You might want to run a search--I specifically remember asking about sticky chambers in my 646 back around 2004, and Hopalong had the answers I needed.

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Appreciate the advice. Re: the load data, I really don't want to add another powder to my inventory. Plus I'm loading th 40s on a 1050 and prefer not to mess with the setup.. I was really planning to use my uspsa loads (N320 w/180 g) in the 646s, and still hope I can make those work.

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Having a little experience with my 646 let me give you what has worked for me with mine.

Sticky chambers:

Mine would start sticking after the third moonclip when shooting major with brass cartridges straight from the factory. I also noticed the chambers were in spec, bit on the small end of the scale. My cure. Using the ever faithful dremel tool and the polishing tip l used the polishing compound FLITZ and polished every chamber until mirror shiney. I then loaded up 15 moonclips of the same load l use in my STI limited gun and shot all 15 clips without stopping to check for stickey. NO problems except the cylinder got very HOT !!!!!! Somewhere before l polished the cylinder holes l did test to see if nickle brass helped with the sticking problem and it did help dramaticly.

So now in major matches you will see me shooting my 646 with major loads using nickle brass (juzt in case)

I did shoot an entire match last month using factory Winchester White box just to test if the brass migt stick and had no problem at all (did not clean the cylinder of the gun all match either).

My major load for my 6" AND Liz's 4" 646 is nickle brass, federal small pistol primers, precision delta 180 grn round nose flat point fmj (closest thing to a real round nose in that weight i have found) and Vit N320 loaded to factory length which puts the radious of the bullet just barely out of the case for more consistant reloads. I dont remember the powder charge zo i'm not even going to guess.

Recoil is a fast impulse that is very snappy that i like. My 625 & 25-2 s more kind of shove compared to the 646 even with the 6" bbl.

I am not a metalurgest ( wow 25 cent word ) so i personally cant help on the upsizing of the 686 cylinder. If you do like toolguy and do make one minor loads should be in order until you can get more info from a metalurgest. It may be you just need to reheat treat, or case harden. Just my thoughts on the upsizing.

Hopalon

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Having a little experience with my 646 let me give you what has worked for me with mine.

Sticky chambers:

Mine would start sticking after the third moonclip when shooting major with brass cartridges straight from the factory. I also noticed the chambers were in spec, bit on the small end of the scale. My cure. Using the ever faithful dremel tool and the polishing tip l used the polishing compound FLITZ and polished every chamber until mirror shiney. I then loaded up 15 moonclips of the same load l use in my STI limited gun and shot all 15 clips without stopping to check for stickey. NO problems except the cylinder got very HOT !!!!!! Somewhere before l polished the cylinder holes l did test to see if nickle brass helped with the sticking problem and it did help dramaticly.

So now in major matches you will see me shooting my 646 with major loads using nickle brass (juzt in case)

I did shoot an entire match last month using factory Winchester White box just to test if the brass migt stick and had no problem at all (did not clean the cylinder of the gun all match either).

My major load for my 6" AND Liz's 4" 646 is nickle brass, federal small pistol primers, precision delta 180 grn round nose flat point fmj (closest thing to a real round nose in that weight i have found) and Vit N320 loaded to factory length which puts the radious of the bullet just barely out of the case for more consistant reloads. I dont remember the powder charge zo i'm not even going to guess.

Recoil is a fast impulse that is very snappy that i like. My 625 & 25-2 s more kind of shove compared to the 646 even with the 6" bbl.

I am not a metalurgest ( wow 25 cent word ) so i personally cant help on the upsizing of the 686 cylinder. If you do like toolguy and do make one minor loads should be in order until you can get more info from a metalurgest. It may be you just need to reheat treat, or case harden. Just my thoughts on the upsizing.

Hopalon

I think this is where I'm heading for now. I have a bunch of 200g jacketed flat points, so I will give those a try along with the 180s.

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