Clyde did carry and use to great effect a cut down BAR. Shortened at the barrel and on the stock, wanting to say stock was about the length of a M-4 collapsed.
Wiki has some pics' from the scene.
Bonnie and Clyde - Wikipedia, the free encyclopedia
Lever action 10ga, Browning A5's, Remmy's all cut down were carried by Bonnie and Clyde. Clyde called them Whippet guns cause they could be whipped out from under a coat. Never heard about them carrying single shots. Kinda of a stupid move even back then. And with the way Clyde was modifing guns they were scary enough.
Can't remember where I read it. Either one of the Shelton's or one of Joaquin Jackson's books. Said that Frank Hammer fired two shots from his Model 8 during the Ambush. One head shot into Clyde one into Bonnie and it was over.