Reading from Paulo Gaspar story on his 297kg world record which he honestly relate in full detail............he is one lucky guy.
I think the logic is simple. Give a fish can pull at least 150% of its body weight, Tuna has more power since it is a super fast swimmer, say 200%, u are looking at 600 kg worth of pull from a Gaspar sized fish.
Technicaly if u shoot a tuna that size and it does not incapacitate the Tuna to a certain extend, u need at least 200-300 kg worth of flotation to tire it but I doubt 200-300 kg pull on its flesh will not tear it. Even the gills probably cant't take consistent pressure to that extend.
Other than good shot to reduce its power, no gun is good enough if you shoot bad. Long RA gun had taken big marlin but it did not full penetrated the fish, Mr. Uyss something the guy. However it hit where fatal and the marlin died on the spot. Paulo tuna goty hit 1 meter from his shaft tip, totaly penetrated the entire fish and it too got stoned. At standard config like the Riffe # Island he uses, 3 x 5/8 band and 9/16 shaft is not even as power ful as my #Baja with 4 x 5/8 and 3/8 shaft.
I think u need a gun that shoot at least for 10-12 feet and can penetrate a 3 foot worth of flesh at that distance to disengage the Slip Tip. Sven's Riffe Island at 4 x 5/8" with 3/8 shaft can do that. The Riffe Blue Water can do that too. But can you get close to a fish that big and shoot where it will be fatal ? Shooting big fish anywhere & anyhow is easy but at that size ur ardenaline might overcome you so much, you might shoot the tuna from 50 feet cause it is so huge you thought it was closer.......that I just decribed myself in that shoe
If u live in places where this kind of Tuna is abundant u r lucky. Get a Riffe Island fully moded and 3 sets of Riffe floats.........but make sure u hit the spine................wezzzz...I think I'll pee in my pants if I see a Tuna that big. The biggest fish I saw U/W was a 6 meter whale shark, that was that.
BTW someone with an Omer also managed to hit 600lbs Blue Fin, check the Omer website.
Greg Pickering video showed a 200 lbs stoned dead shot from some good distance on a custom gun, what brand me don't know. A good shot is the key at this size. I am sure a 100 lbs fish and a 600 lbs fish has the same soft flesh, it is just thicker so heavy resistance from a float has a limit until a tear off eventualy need to happen.
Sorry I am just speculating. Never even seen Tuna bigger than 40kg underwater...