One of the unfortunate side effects of having an underweight speargun is that they tend to kick and reduce accuracy.
To counter this, you can use the new Octosub Ballast Kits, which add weight and heft to your gun, reducing kick and increasing accuracy.
The new ballast kits come in three sizes: small, large and Euro. The small kit is designed for guns with 1-2 bands, while the large ballast kits redesigned for spearguns with 3-5 bands.
Finally, the Euro speargun kit fits 29.5 mm barrels. All the ballast is 1” or 25mm tall and can be used separately.
Depending on the size you need, the ballast kits retail for US$44.99 – $169.99 (~44 – ~150 Euros).
You can find the ballast kit here.