This is a big harpoon gun with cumbersome 4, from the Suns of Fortune. The bipod mount is an attachement from the Core Rulebook and RAW says it can only be used for rifles, carbines and light repeating blasters.

Ok, are those only things with rifle, carbines and light repeating blasters in the name, or could a big harpoon gun that uses Ranged Heavy be seen as a rifle and be included in RAI?

The weapon sling can be used with all ranged heavy, so I can take that instead:) I jumped the (harpoon) gun with this post!

This is a big harpoon gun with cumbersome 4, from the Suns of Fortune. The bipod mount is an attachement from the Core Rulebook and RAW says it can only be used for rifles, carbines and light repeating blasters.

Ok, are those only things with rifle, carbines and light repeating blasters in the name, or could a big harpoon gun that uses Ranged Heavy be seen as a rifle and be included in RAI?

I'd say by RAW and RAI answer is "No".

But there is nothing to say that you can't take a sling or harness.

Well, since the description states that it is thrown by the "stabmen", I'd say it's not a rifle, and mounting either bipod, tripod, sling or harness would help in any way.

BUT, since it also states that it is a "Harpoon Gun", I'd leave some room for interpretation for the GM there.

However, as a general rule, harpoons tend to look like this if mounted on a vessel:

Or, like this if carried by hand:

I don't consider the hand-held one representative of the one in the game, but then the other one would have to have that 200m long flexisteel cable curled up somewhere, which leaves precious little room for either bipod, sling or harness.

Maybe harpoons can be said to be thrown, even when shot from a harpoon gun? Like catapults or balistas and siege weapons of that kind. It says gun, and it is heavy ranged, so I would say it is a gun.

The 200 meters long durasteel wire is pretty crazy though. I guess it`s 4 cumbersome because it`s usually mounted to the bows of boats.

It's clearly a harpoon gun, not a thrown spear. I don't see any problem with using a bipod, tripod, or vehicle mount with one. As always, it's the GM's final call, but that's my opinion.

Keep in mind that in Star Wars, you can get a surprising amount of “cable” in a surprisingly small container. Look at the various pieces of cable-related survival gear, for example.

That said, a ship-mounted harpoon gun should require Gunnery skill, while a hand-held harpoon gun could easily be just Ranged Heavy. Ranged Light would be suitable for something like a crossbow pistol, as opposed to something more rifle-like.

So, a Ranged Heavy Harpoon Rifle with a bipod attachment would make sense to me.