Tim-
Congrats on the rifle performance.
I can imagine your delight!
On the peep sight -- with a peep that close to the shooter's eye, it's acting in the same function as the aperture in a camera's lens.
You're effectively 'stopping down' the exposure, which deepens the depth of field (things close and far away will be in focus at the same time, to a greater extent with smaller apertures) but has the side-effect of lowering the amount of light that gets to the eye.
The discussion of how this works is somewhat complicated, but the benefit is the same any way you look at it.
Again, congratulations on the great performance of your nice little .303
Cheers
Tinker
