I've heard a lot of people say this about BlueDot, and my personalty experience has been different. I've fired 180gr XTPs in a G20sf from a LWD 6.02" barrel in very low light (almost completely dark) and I got very very little muzzle flash. I was pushing the load @1300fps in that barrel so maybe the powder burned more completely than in shorter barrels. I will have to test my g23 in low light to see if the cartridges and shorter barrel make a difference. I do recall reading a post that the older blue dot had a lot of flash and that the newer bottles don't. I can't confirm that, but in my experience it is a loud powder, but I like it.
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