Hi Tim,
During the defence of the Mpofane donga at Isandlwana, it is recorded that some of the NNMC carbines jammed and that Durnford helped to un-jam them (he apparently gripped the carbine with his knees and used his good hand to remove the case)
It is probable that the bottom of the casing came away from the cartridge (caused by the brass heating up during firing), this was a problem not unknown with Martini Henry's (and presumably - I'm only guesssing here without heading for my books also with Swinburne Henry's). It could also have just been caused by the brass expaning in the breech.
That is one reason the British went from the 'rolled' cartridge to the 'drawn' one, which helped with the problem, additionally the Mk IV Martini had a long lever to help extact the 'drawn' cartridge (which had its own extraction issues seperate from the earlier 'rolled' casing)
I do not feel the problem was as great as with the Springfield Carbine used at the 7th cavalry LBH.
Cheers
