BC (flashgap) variation in 6 shot cycle

[HogBob]

I mistakenly posted this in the Intro thread when I joined the forum.

Unlike most posters here, I'm not very knowledgeable about revolvers since I own only two. One is a Model 686-1 with 6 inch barrel and the other is a Model 66-2 with 4 inch barrel. The Model 66 is reasonably accurate (when fired from a pistol rest) but the Model 686 has been erratic since the day I purchased it new. The clearance between the forcing cone and cylinder face as the cylinder rotates is as follows for the Model66:
1 = .007 inch
2 = .006 "
3 = .006 " "
4 = .007 "
5 = .008 "
6 = .007 "

For the Model 686:
1= .006 inch
2 = .007 "
3 = .0075 "
4 = .006 "
5 = .0055 "
6 = .0055 "

When I had the "gunsmith" at the dealer where I bought the 686 check the variation in the gaps, he noted that the they were within "factory specs" and timing was perfect and the revolver was returned by the sales clerk with a bill for $20. I never had an opportunity to discuss with the gunsmith why it was so inaccurate when compared to the shorter barrel Model 66. Does anyone have any information concerning whether the variations in clearances noted above are normal or why one model is so much less accurate than the other?

 

[Hapworth]

Whereas ideally all charge holes would have both in spec and identical measurements for barrel-cylinder gap, some variation is common. The usual suspect is a slightly untrue cylinder face, though sometimes it can be a sprung (bent) yoke, or both.

The b-c gap variations you report are minor, and the gaps overall are in spec and approaching optimal.

Personally, I wouldn't worry about addressing them provided no other mechanical issues.

As for accuracy problems, that's a thorny one with many possible explanations. I'll refer you to this recent thread on the subject as a good first reference for questions to ask and possible issues to run down; suggest a search, too...

http://smith-wessonforum.com/s-w-revolvers-1961-1980/409450-model-66-1-wont-shoot-straight.html

 

[Petrov]

Doesnt S&W machine the cylinders then heat treat them? Probably just some slight variation from heat treating?

 

[chief38]

I mistakenly posted this in the Intro thread when I joined the forum.

Unlike most posters here, I'm not very knowledgeable about revolvers since I own only two. One is a Model 686-1 with 6 inch barrel and the other is a Model 66-2 with 4 inch barrel. The Model 66 is reasonably accurate (when fired from a pistol rest) but the Model 686 has been erratic since the day I purchased it new. The clearance between the forcing cone and cylinder face as the cylinder rotates is as follows for the Model66:
1 = .007 inch
2 = .006 "
3 = .006 " "
4 = .007 "
5 = .008 "
6 = .007 "

For the Model 686:
1= .006 inch
2 = .007 "
3 = .0075 "
4 = .006 "
5 = .0055 "
6 = .0055 "

When I had the "gunsmith" at the dealer where I bought the 686 check the variation in the gaps, he noted that the they were within "factory specs" and timing was perfect and the revolver was returned by the sales clerk with a bill for $20. I never had an opportunity to discuss with the gunsmith why it was so inaccurate when compared to the shorter barrel Model 66. Does anyone have any information concerning whether the variations in clearances noted above are normal or why one model is so much less accurate than the other?

Your B/C Gaps are not too bad and the consistency between chambers is actually not bad either. I have seen a lot worse.

As far as the accuracy goes on the M686, check the barrel and forcing cone area to see if you have lead / copper build up. For that matter, check the chambers as well. I've seen fowling destroy accuracy more than once.

I find that my M586 shoots best with 158 grain bullets and a very clean forcing cone.