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Hi, Phydaux and guys,
Most of the time when a revolver with a tight b/c gap binds up, it is blamed on carbon. That may be the case but more often cylinder binding is caused by heat from firing causing the cylinder to expand lengthwise and close the b/c gap. While some revolver makers consider up to .01" to be within spec, I consider .007" to be close to ideal. Tight enough to prevent gas leakage, but not tight enough to bind even when fired rapidly.
As to some kind of shroud, some ideas along that line have been tried. Iver Johnson had a .22 revolver called the Sealed Eight, which not only had countersunk chambers in case of head failure but had a fairly high ridge around the front of the cylinder to prevent gas escape and lead spitting. (one section was cut away to allow cylinder removal). It didn't actually eliminate the b/c gap like the Nagant does, or increase velocity, but it did prevent sideways spitting and would have prevented gas cutting of the top strap had that been a problem with a .22. (Of course the shield itself would have been eroded with a more powerful round, so it was a case of push in here and it pops out there.) The IJ was a solid frame type; that shield would not be practical on a swing out cylinder revolver since the cylinder could be swung out only at a certain place.
Jim
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