My one and only chain fire was with a .36 loaded with conicals and homemade caps. They can kick off from either direction due to the same cause: incomplete sealing by the cap end or ball end. Bad caps and worn out chamber mouths are usually the culprits. The chainfire did no damage whatsoever. I later chronographed .380 lead roundball (since I used up all my conicals) with 21 grains of 777 both with and without the barrel. With the barrel attached, that load will give a mean of 1117.3 feet per second, or 221 foot pounds energy. With the barrel removed, that same loading only generated 563 fps, or 58 fpe, which is probably not as much force as loading the ball with the lever in the first place. In other words, a chainfire that goes off alongside the gun packs about 1/3 of the force as a ball that goes through the whole barrel.
One caveat that should demand a healthy respect for the phenomenon. This .36 Navy had enough space alongside the barrel for a projectile to neatly exit the gun. However, my .44 1860 does NOT have that clearance, and a chainfire with a heavy 220 grain slug that cannot exit the chamber will in all likelihood grenade the gun. Play with these guns at your own risk and respect them for the weapons they are. And use quality caps and inspect the cylinder chamber mouths to ensure an even swage on the lead.