The Navy has a line throwing kit for the M16 as well. The M14 obviously made more sense for this role, but some (most?) ships simply don't have those any more. The kits consisted of a big metal cup that clipped over the muzzle utilizing the bayonet lug, a spool for the line that attached to the barrel, and a thick rubber recoil pad. The spools tended to sever the line while the projectile was in flight, so the normal procedure was for an assistant (usually a boatswain's mate, but sometimes a fellow gunner's mate) to hold the line bundle in their hands instead; not only did this reduce the rate of shotlines breaking, but it also allowed an experienced assistant to "steer" the projectile in flight.
I've shot a line or two in my time and honestly, I wouldn't want to do it with something light. That's an awfully heavy projectile getting launched and the recoil was substantial.
While there were numerous rules regarding shotline use and acceptable targets, many of them were frequently ignored. It was hard to prove that someone had intentionally targeted something that they shouldn't have, and it was considered good fun to bounce projectiles off of fork trucks, aircraft, ship's decorations, RHIBs, safety observers who hadn't properly taken cover, and basically anything else that looked interesting, with bonus points awarded for "sticking" the shot so that deck personnel on the receiving ship didn't have to chase the line. Here is an example of such a shot. (Note: I was filming from behind my fork truck, as my red hardhat indicated that I was an ordnance handler and thus, I knew that I would be targeted specifically by my compatriots on the Vinson. Also note that this one "stuck" - a very good shot.) In case anyone is wondering, this "accidental" targeting was precisely why we were no longer allowed to shoot lines to aircraft carriers; as it turns out, projectiles can inflict significant damage on aircraft.
Ah, the stories that I could tell. Someday I'll have to tell the one about our "extended range" projectile launching cartridges.
