686 to 646 Conversion

[cornfed83]

A friend of mine is just starting to get into revolvers after being hung up on the "tacticool" side of things for a while. He is quite insistent on the .40 S&W cartridge and does not seem to overly fancy the 610 especially since he wants to use it for carry. I've been looking for a 646 for him but they are not particularly easy to find as most of you know.

So I started thinking and doing a little bit of research and found that the 686 to 646 conversion has been done in the past. Now I'm not sure on all of the details of the conversions that have been done just yet but what I was thinking for him was starting with the 686, an older model with frame mounted firing pin, probably replacing the standard cylinder with an unfluted cylinder for a little bit of added strength, and rebarreling as well just to make sure it will be more apt to handle the pressure when using less steel between the bore and the frame.

This idea is still in its infancy for me so I'm open to any suggestion and advice as well as experience anyone may have on this conversion.

Finding a capable gunsmith won't be a problem, I call mine Dad. I just haven't ran the idea past him yet so I'm posting here first.

 

[scooter123]

Personally, if you want a reasonable price, I find both the 646 and 610 difficult to find. I have a 6 1/2 inch 610 and one of my biggest regrets is that I didn't purchase a 4 inch 610 at the same time.

I seen a couple of potential issues with your idea.

One is that it will NOT be at all easy to find a 40 caliber barrel for the L frame. So, your father will not only have to be equipped as a gunsmith, he will have to be equipped as a barrel maker. Otherwise he'll have to purchase a full 40 caliber blank and machine it complete to profile.

The second issue is a potential safety concern. Every singel 646 was equipped with a titanium cylinder and I am not aware of S&W ever offering a stainless steel cylinder for this model. It's the main reason why I didn't purchase a 646 when one popped up used at a local gunshop, I don't like the sensitivity to careful handling of the titanium cylinders and wont buy a revolver with one. However, S&W may have chosen to use a titanium cylinder on the 646 simply because a stainless steel cylinder wouldn't have been strong enough for the 40 caliber in this diameter.

Now, on a positive note there is one option that you have not considered that is still relatively easy to find. That is the model 310 Night Guard. It's just been recently dropped from the catalog and never was that popular because they are light enough to be a bit unpleasent to shoot. However, they are light on the hip and that unpopularity means that prices are reasonable and they are somewhat easy to find.

 

[youngda9]

686 in .357 will be much more potent than the .40. A 3" 7 shot version would be great for carry. The .40 will require moon-clips also, PITA.

For the cost of what you're looking at you could get a 696 which would be awesome also.

Since he is "just getting into revolvers" it would be wise to choose a standard offering until he decides he is going to "stay into revolvers", thus justifying the $$ for a custom rig to suit his needs.

 

[WC145]

Scooter's right, the Ti cylinder was for strength, a steel cylinder doesn't have enough meat around the chambers to handle the pressure.

I would think that it will be almost impossible to find a .40 barrel and cylinder for sale as they all went into guns. The 2003 run of non-PC 646s used up the cylinders left over from the 1999 run of PC guns.

If he really wants one tell him to keep shopping, they come available from time to time. I sold mine here in the forum classifieds a few months ago.

 

[cornfed83]

The plan was to buy a blank 40 cal barrel turn that down to appropriate length and profile. Pick up a 686 6 shot unfluted cylinder and expand the chambers to appropriate dimension for 40 S&W, unfluted so that it has the extra beef there to help with the pressure. I've read that this conversion has been done in the past, I just haven't read up on the exact details just yet.

 

[scooter123]

The plan was to buy a blank 40 cal barrel turn that down to appropriate length and profile. Pick up a 686 6 shot unfluted cylinder and expand the chambers to appropriate dimension for 40 S&W, unfluted so that it has the extra beef there to help with the pressure. I've read that this conversion has been done in the past, I just haven't read up on the exact details just yet.

The problem with your theory is that the fluting on the cylinders doesn't weaken the cylinder a bit, however it does reduce the moment of inertia. The weak spot on any cylinder is the Outside Diameter when it thinest at the bores for the chambers.

Now, there is room in the frame window on the L frame for a slightly larger diameter cylinder, so it might be possible to gain another 0.03 inch of wall thickness. However, that larger diameter will then mean that a new cylinder stop that is designed to latch in on a larger diameter cylinder and I suspect that the end requirement may require a total re-design of the lockwork. It might also be a re-design that in the end would prove fruitless, because I suspect that if S&W could increase the diameter of the cylinder on the L frame a bit more they would have done it.

BTW, I understand the appeal of the 40 caliber. Range ammo for a 40 caliber is less expensive than 38 spl. range ammo. At one point the cost difference was over 6 dollars per box. That is one factor that led me to purchase my 610 when it was available and I have put several thousands of rounds downrange with me 610. From a Defense Ammo standpoint it's even better, the 40 is both less expensive and MUCH MUCH easier to find. In my area both Ranger-T and Speer Gold Dots are common at many local gunshops while suitable Defense ammo in 38 +P or 357 Magnum can be hard to find.

 

[wantmoresmiths]

If your friend is dead set on a 646, his options are limited, post a WTB ad here for the 646 or watch for one to come available on Gunbroker. I shoot with a gentleman who uses his 646 for IDPA and ICORE. He told me that shooting the 646 can be somewhat difficult due to the light weight of the titanium cylinder. He tried quite a number of different loads until he found one that was comfortable to shoot. I, on the other hand lucked into a 5" 610, and it is one of the most accurate guns I own. My son has the 6.5" version of the 610 and is thrilled with the way the long barrel dampens recoil.

As far as taking a 686 and chambering it for 40 S&W, you will want to follow this thread. Be sure to read all the way through, lots of good ideas. 40 cal 686? - Brian Enos's Forums... Maku mozo!

 

[TSQUARED]

Personally I believe you would be better off financially paying the premium for a S&W646 than investing in the conversion of a 686.

 

[Stainz]

I've had a long time to regret not buying a last production run 646 from a lgs - he closed them out at $449! I knew it was a deal then... but waited too long - his last one was gone by the time I had decided. A couple of years earlier, I had bought one of his last new 296's ($349) and 696's ($439!). Hind sight is always 20-20. In retrospect, the 5-shot .44 Specials were fantastic buys.

About the .40 ammo... it was also the only ammo you could find at WallyWorld during the last great run on ammo, some 3.5 yr back. Must be a message there.

Stainz

PS If I were the OP and couldn't find the OEM Ti cylinder, I'd scrap the conversion idea and hold out for a 646.