I'm wanting to late one afternoon photograph at my club some black powder revolvers being fired and capture the flame coming out sideways from the cylinder as the ball is pushed into the barrels forcing cone and also the flame coming out of the muzzle.

For target practice using these .44 caliber BP pistols, usually its 20 grains of FFFG black powder and 20 grains of a filler such as polenta so as to tame the pistol down a bit for competition accuracy and also wear and tear on the competitor. Depending on the flash that can be upped to the full 40 grains of FFFG if more flash from the pistol is needed.

The camera is going to have to be to the right hand side of the shooter and a good way back as there is lots of cr@p that comes out of these BP pistols with burning powder, inert filler and the grease to seal the balls in the cylinders and I don't want any of this corrosive stuff on my camera or lens.

My questions are that the shooting line is under a roof so it will be fairly dark late in the afternoon to start with as the sun will be going down and not much light coming in from the grassed outdoor 50 metre range.

What settings would anyone suggest that I should use on the camera as a starting point? I would dearly like to catch the flame being emitted out of the gap between the cylinder and barrel, out the end of the barrel and the barrel of pistol raised up in recoil.

The D850 with battery grip can shoot 9 PFS.

Any help or suggestions much appreciated.