So what exactly goes wrong with a 686 that is fed a diet of .357 loads for an extended time?
How many rounds until they are "scrap"?
How do you know when the barrel is toast ? How many rounds typically ?
When Smith L frames (586/686) are fed steady full house magnums, their cylinder lock-up loses that bank vault solidness. You will notice that under lock up, the cylinder would rotate, in my rough estimate, two degrees or more. I had a 686 I bought from a buddy that probably shot 10,000 magnums during the heyday of metallic silhouette, that was clearly more loose than 2 degrees. It was still almost as accurate as my newer 686.
My current 686 which locked solid when shot only 38 specials, started to have discernible looseness after only 100 magnums.
Can't tell you how many rounds till they are crap, cos I've haven't reached that stage. Could be 30-40K full mags, who knows perhaps somebody with the experience can chime in. But I like my guns tight. So now, my Smiths are shot up to 38 +P+ loads only.
My GP100 doesn't know the difference between 38 spl and magnum
A barrel is worn-out when your groups expand noticeably. Say you could shoot 3 inch groups at 25 meters. Once you notice a progressive deterioration, say to 4, then 5...with all factors remaining the same like your skill/eyes, shooting style/proficiency, ammo load etc, then perhaps the barrel is shot out. With lead .38 reloads, I've heard of PPC competitors shooting 200,000 rounds and still going strong. With jacketed full house magnums, could be much much less, perhaps 30K.
Loss in accuracy can also be a result of wear in other parts, though.
Having said all that, I love Smiths and Rugers for what they are. Smiths have that sweet DA/SA trigger although I don't care much for its SA trigger which is the best stock SA trigger you can get, but I almost never shoot SA anyway. Smiths have the best revolver "look", IMO. I love my Ruger GP100 and Security Six. They may not have the sleek design and trigger of Smiths, but mechanically they are superior with acceptable triggers that get better with use. Ruger triggers can be worked on to approach the feel of a Smith but I doubt if they will equal a Smith's. As well, both the GP and SS seem to fit my hand better than the Smiths.
If you will buy a Ruger, buy the IOWEGAN BOK (book of knowledge) for the GP/SS/Redhawk series, go to rugerforum.net. It will show you how to fine tune your Ruger if you are so inclined. Edit: Sorry, I just checked availability of this fine publication but IOWEGAN, the author said he will print some again in the fall. I was going to buy one because my BOK that the author graciously sent me for free when it was still available for free, does not have the SS/Redhawk updates.
