Your Stren 4 pound is breaking at 6 pounds. Here is a chart that shows diameter of braid and mono lines and their breaking strength. This under rating of lines started around the 70’s and it was because of bass fisherman. In the US market you will need to look at the diameter of the line to figure out its actual breaking strength as the pound rating is almost always not true. There are a few US market lines that rate line correctly, but very few.
Regards
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