I'm currently doing my brake lines on the sj using Kunifer, Copper/nickle pipe but i'm having problems with the flares splitting on the edges. I'm using the tool pictured below after having too much trouble with the cheep shite ones that i already have from a couple of years ago. The tool flares perfectly on copper but i know from research not to use copper, i though maybe the tool is only good for copper but it specifies in the description of when i bought it that is can be used for Kunifer and even steel, which i doubt.
The pipe is 10% Nickle and 90% copper, so i guess the nickle reduces the work hardening in the alloy.
I have followed the instructions that came with the tool after having bad results on the first flare in picture 2 by not following them.
So basically does anyone have any ideas on why it might be doing this or had experience with this happening to them? I've spent a long time researching the do's and don't of flaring and brake lines as it's the sort of thing i don't want to fuck up. I'm just confused at this point.
Here's the tool

First flare without using instructions

Other flares


