Hello, it T'was a long long time ago, in a faraway land. No...actually it was here. But it was a long time ago. I think it was on my second shot, and two adjacent chambers on my left also went off. Oh, I guess that's obvious...the empty chambers on my right most likely would not go off. !!!!
Don't remember if any caps detonated. I think I was using wads, but can't say for sure. I do know that I shot the gun (1860 Euroarms Colt) for many years before that without wads, using black powder. No greasy kid stuff over the balls/chambers.
The charge was 30 grains of 777, by volume. Caps were pinched to stay on the nipples. That may have been the problem, the much higher burning temps of the 777 may have ignited the other chambers through the nipples, whereas the black powder never did. ? On the other hand, the much higher temps and pressure may have been enough to flash past the balls. ?
It could have all been a coincidence, but I find it "funny", that in like 40 years the pistol never chain fired before, or after trying 777. ? And, that it was only on the 7th shot, with 777.