In order to provide up-to-date 357 SIG flash information for our readers, please feel free to e-mail to provide updates and/or corrections. I do not have access to some 357 SIG ammo, and do not generally have a budget to test factory ammo. Thanks.
 
Factory Ammo:

Blazer: Has a little bright white flash.

CCI Lawman: Has an orange/red flash about 6" in diameter.

Corbon 115g JHP: No muzzle flash.

Federal "Personal Defense Ammo" (PDA): Has a very bright flash with a ball of white light at least 18" in diameter.

Hornady 124 HP: Very low flash.

PMC Eldorado: Has 8" diameter orange flash.

RBCD 60 grain TFSP: approx. 9" long and 5" wide; fairly bright orange/white light -- tested in daylight only.

Remington Golden Saber Hollow Points: Very bright flash that can adversely affect night vision.

Sellier and Bellot: Has no flash.

Speer Gold Dots (with yellow primer): Almost zero noticeable muzzle flash.

 
Gun Powders

High flash powders:

Blue Dot (Alliant): Very bright flash about a foot wide or so.

Power Pistol (Alliant): Very bright flash about a foot wide.

Medium flash powders:

AA#9 (Accurate Arms): This powder varies. Sometimes it flashes fairly large (almost a foot), but is uneven and not a really bright ball shape like the high flash powders. At other times, it produces a very low orange flash. Yet, the velocities are very consistent and the standard deviation is low.

Low flash powders:

AA#7 (Accurate Arms): Very low flash (3").

HS-6 (Hodgdon): Very low flash (3").

N350 (Vihtavouri): Very low flash (1").

Universal (Hodgdon): Very low flash (1").