I looked too, but the 'beretta" is squared and has not such a fixation line as it would be for an helmet, but he would have an armour.
If I had to paint, i would just erase it and only keep his left hand hanging !!
Not such a hard work, and no single canvas painting is representing him exactly the pose that he has on this engraving . I even looked at the paintings of Cardinal Mazarin ...
