make assurance doubly sure meaning in English

加倍小心, 特别慎重

Now that i had a moment to myself , i lost no time in changing the priming of my pistol , and then , having one ready for service , and to make assurance doubly sure , i proceeded to draw the load of the other , and recharge it afresh from the beginning
现在我可以暂时歇口气，我抓紧时机把手枪换上弹药。一支已准备好，但为保险起见，我索性把另一支手枪也重新装上弹药。