They're wrong. As mentioned above, grease does not prevent flash over and hence chain fires. Grease is used to keep BP fouling soft to aid cleaning.
Some time in the late 70's early 80's, Sam Fadala, Mike Venturino and Garry James did an exhaustive study for Guns & Ammo magazine. They found that no matter how they tried, they could not induce a chain fire. Ian V Hogg then looked at the phenomina for the History Channel and I believe it's the one and only time a chain fire was filmed by chance!
The conclusion was that the "flash over" actualy occured at the rear of the cylinder and was due to either ill fitting caps, worn nipples, a leakage of fine powder grains during the loading process or a combination of each or all.....
Like also mentioned, in 33 years of shooting revolvers, I've never seen, nor heard of anyone who has witnessed a chain fire.
Health & Safety nazis........
Most of the lads in our club use Trex lard, seems to do the job, and alot cheaper than grease or bore butter.
Jon
AA S410 .22, Anshultz .22LR, Tikka T3 Continental Heavy Barrel .223, Pietta Old Army .44BP
Hatsan Escort 12g, SAKO Quad 17HMR, Marlin .44 Underlever, Webley Single Barrel Bolt Action .410g