I don't use 3/4" (19mm) bands myself, and have rigged only a couple of spearguns with this rubber, those were long guns in the 120cm range. I was finishing building a 90cm gun today, and it was time to cut the bands. Being such a short gun I wanted it to have some pop. So I figured I'll start with a conservative ratio of 1-3, in other words %300. I measured the distance from the muzzle to the furthest tab at 91cm, so I cut the band to 30cm. If this sounds way short it's because I'm using the Meandros muzzle, so there are two of these bands.
I tapered the bands, tied them to the muzzle, and fortunately before continuing on to tying the wishbones, decided to try and pull them as they looked damn short. I folded up a towel and put it on my chest, grabbed the bands and pulled hard.. At this point I started laughing out loud :laughing: there was no way in hell I'd be able to load this gun. Wasted rubber, wasted time, I had to do everything over. I guesstimated that 36cm would be doable, and went with it. I can now just barely load this gun. I have good upper body strength, and have loaded many guns. I don't know the person who's going to own this gun, I hope he can load it. I can say for sure though that if he can, this gun is going to zzzing.
So the stretch ratio ended up being 1-2.5 or %250. Keep in mind this is the Speardiver small ID rubber. Is this a normal stretch ratio for a 19 mm band? The fact that the bands are tied into the muzzle and missing the little extra that would thread through a conventional band slot is another factor to consider.