Bagging Barrow Law is a pretty easy as it's only a short 2km walk from the parking at Wedder Leap.
Although it stands at 419m, you are already 256m up at the parking area, so just a mere 173m of climbing.
Follow the route above or find it on OS Maps.
If you continue north from Barrow Law you will also be able to bag Ward Law and Little Ward Law before ending up at the border ridge and the Windy Gyle Trig Point.
To make a day of hill bagging you can follow this walk to Yearning Law, Border Ridge and Windy Gyle. Look out for the little marker/grave stone for Murder Cleugh which has a gruesome story.