I THINK the width of strap I use is 3/4” (19mm), but im not 100% sure on that one
I know its 4/5oz leather that I use for the thickness
As for the length, thats kinda still up in the air. I keep playing around with it and even this new sling I made for the tutorial I feel might be just a touch too long compared to the film one. But roughy the length of the blaster is what Id reccomend shooting for give or take an inch or so