You don't state specifically WHERE the string is breaking, but if it is right at the tuning machine post, you may have to either change scale length selection or move to a different brand. This is primarily a problem with smaller tuning machine posts...the string winds around okay, but the main body of the string ends up winding around the post (rather than the tapered portion)...because the post is so small, the string is too thick to make a tight enough bend, and the core wire gets broken as the string is crimped around that narrow radius. I have this problem with my Sadowsky 5 string bass- D'Addario long scale strings are fine but any super long scale B strings break immediately at the post upon install. You can check first by taking the loops out of the new string and then holding the ball end right over the spot in the bridge where it will reside. Then stretch the string to the machine head that it will be mounted on, and see if the windings taper before that point. Note that this applies mainly to 3/8" posts- 1/2" posts are usually fine.
sorry for the novel- good luck!
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