Question about shotgun ctb

[jisatsu88]

Will this work? I'll have the shotgun on the floor just like in the picture and I'll have to hold the barrel because the shotgun is long. I know holding the barrel is advised against but I took it to the range to try shooting it while holding the barrel and it's fine until it starts to get hot which is like a few shots in. I'll be using 12 gauge 2 3/4 buckshot for ammo. I'll have the shotgun in my mouth and shoot in the same exact angle as the picture.

 

[Eudaimonic]

I think the angle should be 10-15 degrees

 

[Kbeau]

I think the angle should be 10-15 degrees

As in higher or lower aim than the image? Is this the best ammo to use?