A colloquial variant of the proverb meaning that by trying many times even an unskilled person can occasionally succeed.
最初はミスが多くても、続ければ上達する。下手な鉄砲も数撃ちゃ当たるからね。
Even if you make many mistakes at first, you'll improve if you keep going. After all, even an unskilled shooter may hit the target by firing many shots.
応募は数勝負だ。下手な鉄砲も数撃ちゃ当たると思ってどんどん出そう。
Applications are a numbers game. Think 'even a poor marksman will hit with enough shots' and send them out steadily.