View Single Post
 
Old 10-10-2018, 03:09 PM
HorizontalMike's Avatar
HorizontalMike HorizontalMike is online now
US Veteran
 
Join Date: Nov 2013
Location: South Central Texas
Posts: 585
Likes: 848
Liked 492 Times in 218 Posts
Default Cylinder Gap on Old No Dash 686

After sending off my new-to-me 686 No Dash to S&W for some service work (cylinder release sticky and for "M"), I finally got a chance to fire it and site it properly. I also took the time to take some measurements of the cylinder gap on this gun, as well as my original bought new 686 No Dash. My measurements on at the bottom of page.

I followed the advice that I found on the following website:
castboolits.gunloads.com/Excessive-barrel-cylinder-gap

Check the barrel-cylinder gap WITH EMPTY BRASS IN THE GUN!

PASS dimension is the largest feeler gage size you can insert between the barrel and cylinder, protruding from both sides of the frame window, which permits pulling the trigger six times to rotate the cylinder through a full revolution without binding up.

HOLD dimension is the size which in the same test condition as above causes the cylinder to bind before completing a full revolution, with fired brass in the gun (substitutes for "rear gage").

END SHAKE or END PLAY is the difference between two HOLD measurements, taken both with, and without "rear gage" in place.

New builds before proofing min pass 0.003/hold 0.004

After proofing max pass 0.006/hold 0.008

Customer service max pass 0.007/hold 0.009

Cylinder gap over 0.012" should not be fired as you may stick bullet in barrel.

End Shake over 0.003" stretch crane arbor then recheck gap.

If HOLD gap after over 0.009 refit with "long" cylinder.

Current specs may vary, but this is how I built them in the 1980s.


My Gap measurements

My new-to-me 686 recent GB purchase:
  • Pass = .009"
  • Hold = .010"
  • Endshake less than .001"
Is the above too much gap at this point?
Or should I not worry about it at this stage and shoot the Kayrapp out of it?...



My original 686:
  • Pass = .005"
  • Hold = .006"
  • Endshake less than .001"
Reply With Quote