I believe that there's room on this board for different perspectives and references. After all, there must be close to 20 years of collective experience in the THR black powder forum archives.
For example, regarding Colt cap & balls:
" madcratebuilder said:
The old Colt specs called for .006-.008 for the cap and ball revolvers. You can run a closer gap but risk binding if you have any powder residue build up. Colt had this problem with the Walker and changed the forcing cone shape with the Dragoon model for less surface area contact.
I've shoot these with as much as .018 gap and see little or no difference with the same model at .008.
To close the gap you have to set the barrel back, fairly easy on a open top, requires machining on a top strap model." --->>>
https://www.thehighroad.org/index.p...linder-gap-on-a-colt-type-bp-revolver.588340/
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In another thread about SAA's and black powder cartridge revolvers, mec said:
" Most revolver shooter would go looking for a gunsmith if the gap exceeded .005. One famous in-print guru used to say that anything over .003 was unacceptable.
I thought I remember that S&W allowed a .010 gap and this is what somebody said on the Pistol Smith board, "Smith Wesson's official spec used to be .003 to .010". I have seen new SW guns with gaps as wide as .015". "
Driftwood Johnson replied:
" Anyway, my favorite reference for the SAA is Jerry Kuhnhausen's book The Colt Single Action Revolvers Shop Manual, Volumes 1 & 2. In it he recommends a barrel/cylinder gap of .006 for jacketed bullets and .008 for lubed lead bullets. I have many single action revolvers; Colts, Rugers, and clones. The vast majority of them have b/c gaps of between .005 and .008. For some reason, many shooters seem to think that a wider b/c gap is preferable for Black Powder, believing that the increased fouling needs more clearance between barrel and cylinder. However my personal experience is that gaps of between .005 and .008 perform just fine with Black Powder cartridges.
In another book, The S&W Revolver Shop Manual, Kuhnhausen states that most modern S&W revolvers leave the factory with a gap of between .003 and .006. In this book, he states that for Smiths, a gap of .008 is considered max for good performance, and a gap of .005 or .006 is considered ideal. I have not gapped any of my modern Smiths, but I will measure a few over the weekend just to get a feel for what they are.
I can tell you that this old 38-40 Bisley Colt, made in 1909, has a gap of .008 and it shoots just fine with Black Powder.
This old S&W 44 Double Action, chambered for 44 Russian and made in 1881 is a bit worn. It has a pretty wide gap of .015, but it shoots just fine with Black Powder cartridges without any lead spitting. " --->>>
https://www.thehighroad.org/index.php?threads/do-or-dont-1st-gen-colt-45.752565/#post-9481604
Only the first quote actually pertains to cap & ball guns, but it shows that there's room for a host of informed opinions about barrel cylinder gaps [or clearance] from different sources.
Perhaps it's due in part to the purpose for these revolvers having changed from being primarily military & defensive arms to largely being target pistols and recreational weapons, rather than a gun that one's life depends on.
Much like the reliability vs. perfection of performance dichotomy of many military based weapons.