Description bugs.
Pretty much all the descriptions for rending/brittle are borked after the rending rework, and brittle stacks are 2.5%. Only the Can Opener on Ripper got doubled after a subsequent update to apply the same amount, in this case max 16x2.5=40% in 1 poke.
Sadly Shattering Impact on Rumbler wasn’t doubled, seemingly intentionally, so it’s likely better to go with Adhesive and Blaze Away now if you can.