I've seen an oddly stocked rifle made for a wheelchair bound target shooter who had been mangled by WW1 shell fire. I think the caption said the stock was rested against the chest.
If I'm not mistaken some early Crossbows and pre musket firearms were also rested against the chest rather than the shoulder, especially if a breastplate were worn. Shoulder armor prevented tucking such weapons into the shoulder.
I don't know much about Arab warriors but I have seen an Arab breastplate ,at a local antique shop years ago, made from a section of a Crocodiles back. It had built in sheathes for three daggers, two curved and one very long straight Poinard style that might have been a relic of the Crusades.