[IDriveB5]

The cylinder gap in my 686 measures 0.007" and the gap in my SP101 measures 0.008".

Reducing that gap to, say, 0.004" would gain me some velocity, but how much?

[Jim K]

Correcting the B/C gap will require a lot of expensive work by a top quality pistol smith and believe me, won't be worth it. The velocity gain would be insignificant, less than the normal variation in rounds from the same box. But you could run into cylinder binding from powder residue or from the cylinder heating up and expanding lengthwise after a few shots. In fact, an .007-008" gap is about ideal.

Jim

[The Lone Haranguer]

If it ain't broke, keep fixing it until it is. ;)

The barrel has to be unscrewed from the frame (an extremely tight fit requiring special tools and fixtures), the shoulder machined, the threads recut so the barrel indexes correctly, and the forcing cone recut and squared - all this for .002 of an inch which is not significant.

[Kor]

Only if you experience "side-spitting" when firing the gun due to hot unburnt powder granules escaping through the barrel-cylinder gap - and even then, it's not that big an issue unless you're shooting on an indoor range where the particles bounce back off the lane partitions and sting you on your hands/arms/face.

[The Lone Haranguer]

With those gaps, the side blast should not be excessive. There will always be some, however. I've seen photos of coat pockets that a revolver had been fired through. Obviously there was a hole where the bullet exited, but there were also fairly large tears in the fabric - one on either side of the bullet hole - from the cylinder blast.

I had a S&W 66 c. 1995 with a noticeably wide flash gap that (by my specially calibrated "eyeballoscope";)) I estimated at .012" , however, and the side blast was worse than the muzzle blast. I had this repaired under warranty.

[def4pos8]

I recently sent my Model 66 to Mag Na Port for some work, primarily venting of the barrel. I also asked them to cut a "target crown" on the barrel and do an "11-degree" forcing cone cut. A side benefit to all that was that they re-indexed the barrel such that my barrel-cylinder gap is in the vicinity of .004 to .005 inch.

I'm pleased with their work. The cost wasn't crazy. The revolver shoots better. I'm happy.

It's a possibility. . . .

[dagger dog]

I found out how critical cylinder gap can be, when setting up a Dan Wesson .357 Pistol pack , it came with a go no go gauge for setting up the gap. 0.004" is too close for reliable clearence on weapon used for self defense..

[unspellable]

I've actually run tests on this question. Using a Dan Wesson in 44 Mag and one in 22 LR. In order to be statistically significant, I ran 30 rounds at each gap setting. From 0.003 to 0.008 the difference is way too small to justify the effort unless you have an adjustable gap ala Dan Wesson. Around 0.012 the gap will begin spitting junk back in your face. (The 44 Mag load was a factory load that was fairly mild for a 44 Mag.)