I'm no expert, but one thing that struck me about Collier's revolving flintlock pistols is that they appear to have less open space for the possibility of chain-fires than in some later revolver designs.

Looking at this I don't see any exposed touch holes other than the one positioned directly under the frizzen, and the addition of the shield that covers the front of the cylinder looks like a decent addition to improve reliability:

http://www.horstheld.com/0-Collier.htm

It looks to me like Collier's pistols had a similar design to some of Allen and Thurber's pepperbox pistols with the shield covering the other cap nipples that weren't in use:

https://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/AllenAndThurberPepperbox.jpg/1200px-AllenAndThurberPepperbox.jpg

Compare that to something like a Colt Dragoon '48 with exposed cap nipples and an open cylinder:

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Colt_Dragoon_Mod_1848.JPG/1920px-Colt_Dragoon_Mod_1848.JPG

Is there any historical evidence on Collier's flintlock revolvers indicating how common/uncommon incidents of chain-firing were on them?

I would make an uneducated guess that a bigger safety risk on these guns could be the possibility of a spark from the pan igniting the powder in the priming dispenser. Was there any internal feature that tried to prevent that?

I cannot find any mention of chain fires with these guns. That is probably because it was sealed at the mouth of the cylinder and the touch holes were positioned in the cylinder so that when the pan is primed there is also a pretty effective seal. Interestingly the frizzen with powder reservoir has internal parts which do meter the priming charge, filling the reservoir when the frizzen snaps back and priming when the frizzen is lowered on the pan.

The cylinder must be turned manually for firing. The cylinder is pulled back, turned and released. It then moves forward on the barrel to seal the chamber. Later models had a plate covering the face of the cylinder which could be removed for reloading.

All in all, this was an advance in that the user could fire five shots without reloading. However, the mechanism was expensive to make and out of reach of most, cost wise. It was also of dubious military value because of the cost and complexity of the mechanism. Rifles, smooth bores and pistols were made of this design. They are very rare these days.

Thanks Lin, that all sounds consistent with what little info I've managed to find on these so far. Definitely rarities today as you say, I saw one go at auction for over 60 grand! https://www.rockislandauction.com/detail/69/1114/collier-patent-flintlock

I think you're right that their complexity and cost were the primary factors keeping them from widespread adoption. That and the fact they came just a bit too late, percussion guns would begin to phase them out in just a couple decades. Too bad there don't seem to be any repros around, would be interesting piece of history for target shooting.

I did hear that a small number of Collier's revolving flintlocks were purchased by the British military for use in India. I can't find any record on their service reputation though, or whether it was a combination of long-guns and pistols or just one of the type...