Most folks know that you risk a mag tube detonation if you slap the nose cap shut on a Henry, letting the follower smack down on any thing but a full mag. Somewhere I've read that it happened with RF ammo back in the day as well due to the fulminate of mercury priming mix.
It happened with Spencers as well, as witnessed by a letter from Col. Hiram Berdan to Col. Thomas Scott, Asst. Sec. of War, taken from "U.S. Sharpshooters - Berdans's Civil War Elite" by Roy Marcot.
"Colonel
While trying the Spencer gun yesterday, the butt of one of the cartridges burst, and some powder blew through the slot in the gate, into my face and eye, destroying the entire sight for the moment. The surgeon thinks, however, that he will be able to save it.
I am unable to go out today, and write to ask if the agent or manufacturer of the Spencer gun is now in the city. If so, will you be kind enough to request him to call on me, that we may see if it is not possible to guard against similar accidents with the new guns. The bearer, Mr. Doherty, will take any note or message you may desire to send.
H. Berdan, Col. Commanding U.S.S.S."
The Sharpshooters came very close to adopting the Spencer as their rifle but the supplier could not meet the demand at the time.
It is uncanny how similar the Spencers look like the Sharps millitary rifles and carbines.