Other posts about accuracy issues got me thinking.
My gun shot like doo doo, crown looked like doo doo,, sent back to smith to crown barrel.
It came back and I shot an off hand group ran som eplate racks,,, seemed to be fine.
Put up for a couple years.
Now got a pistol bench rest and working up good loads,, It shoots ok, but not all impressive.
Another poster stated accuracy issues are farther back..
So,,,,, did some measuring.
1 I had a squib,,, load with primer only got swithced when i was setting up dies,,
So VOILA land and groove measurement once I wacked out the bullet.
Broke out calipers, a new box of Hornady XTP's .357 and some new bayou cast .358.
So what do I get ? pretty shocking,,, Throats appear to be .357.. I can push the XTP through with a plastic pen. A bit of resistance,, I thought it would fall,, but I have to push a bit Although when I mike them after pushing through all 7 cylinders dia is still .357
So looking like a .357 throat,,, Ideally I think it should be at .358, moving on to barrel
Was getting .352 ish groove,, but then noticed I cant figure out how to measure land and groove , As on this gun the Land is 180 out from the groove,, turned it a hair off to catch both grove, seems I get a .352-.351 issh area when I rotate bullet

So ? what to do ? can ream cylinder throats to .358,, but thinking even though barrel seems tight, if it is at least tighter than throat, none of this is a problem

Joe4d, I bought a new 686 pro like yours a few years ago. Shooting over a rest, and trying a variety of factory ammo, accuracy was dismal. I checked timing, B/C gap, end shake, bore, charge holes. Everything appeared to be as it should. Till I checked the barrel crown, if it could be called that. It was about he crudest I'd ever seen on a new gun. S&W recrowned the barrel, and afterwards the gun was as accurate as my other S&W revolvers.

I don't know how to accurately measure S&W groove diameter either. But as long as throats are not smaller than groove diameter, Id just shoot the gun unless accuracy is obviously poor......ymmv

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NRA Life, COTEP 640

You got me worrying about my new 686 pro. I just bought one yesterday.

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Fear only God

Joe4d, you say accuracy is not at all impressive. What kind of groups are you getting and at what range? I've got a 5" PRO that had some issues with the hand not being correctly fit but accuracy was never an issue. I have found with all of my .357's that bullet weight and velocity seems to be kind of important. I don't have a bench rest. When shooting for accuracy to test loads etc. I shoot sitting, leaning back against the bumper of my truck with my knees up to support my hands and the pistol. Actually a very stable position. At 20 meters it will group around 2" with the occasional flyer caused by me. With my vision and skill level I figure that's the best I could do regardless of what I'm shooting. It does seem to like lighter, faster bullets though (as do most my .357's). For me at least.

DO NOT ream the throats to .358. They are perfect as is. The S&W barrels have 5 lands & 5 grooves so it is difficult to get an accurate bore diam. measurement without special measuring tools. Another area related to accuracy is the forcing cone. If the crown really is fixed now, the forcing cone may need some attention. Most S&W barrels have good rifling with mild to wild f/c and crown problems. Once the 2 ends are made good, 99% of the time it will be match grade accurate.

Thanks guys,, shot it again today on a pistol rest from 25 meters,,, Just not impressed 4-5" groups ? So whats up with forcing cone ? needs to be reamed ? Not getting any lead shavings or spitting that I can see.
I got dun and broke out my 6" bull barrel STI Limited gun I havent shot in 5 years, but I KNOW it will shoot an inch at 25...
Well groups were in the 4" range. So maybe it is just me I cant see.
Is it possible I have the issue where the barrel is compressed at the frame ? The sluged bullet I had was a squib that went half way down barrel,,, so it is possible throat is smaller than barrel

If the barrel is compressed in the frame, it won't shoot groups either. But if a known shooter is doing the same as the Pro 5", then maybe the gun is OK now.