I've used the XLR 250 Kill Light and the Wicked 400 with two batteries.
The 403 has an intensity control knob. With the others they are at full power. With those you should hold your rifle vertical, turn on the light then slowly bring the beam down on the animal. Sometime that even spooks them. The 403 not only telescopes from wide beam to narrow (sqaure) beam but the intensity can be turned all the way down allowing you stay on target and slowly turn up the intensity. IMHO works much better. The only draw-back is that because of the IC knob the light is easily turned on in your pack. I either make sure the I/C is turned all the way down or take out the battery until I'm ready to turn on the light.
old style without I/c
new light with I/C
As I use a number of rifles I also got the universal quick mount. I can change from one rifle to another in just over a minute.