The same was happening to my big shock blaster and I found that squashing the darts for 4 seconds will solve this issue.
If it isn't working, try squish harder, I did it so the dart was basically flat.
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EDIT:
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PS: the darts will drop a bit more, so if you are using this in an actual war, make sure you aim up a bit more. NOTE: they won't drop too much, so don't worry.
The same was happening to my big shock blaster and I found that squashing the darts for 4 seconds will solve this issue.
If it isn't working, try squish harder, I did it so the dart was basically flat.