One factor that can affect group size in cooler weather, especially on calmer days, is warm air from a heated barrel roiling the view through the scope.
John,
Hot or cold temps.
If the barrel gets hot enough.
No matter the contour...
It can mess up your view.
I get this black paper backed foam board at office max and cut it to fit.
Velcro does the holding.
If you get it to close to the brake.
Bad things happen.
But in general, a barrel shade will block the heat wave off the barrel.In most hunting situations, I cant see why a person would be shooting enough to need one.
For 1000 yard BR it kinda comes in handie...
For my 17lb "light" rifle I like a muzzle diameter over an inch.
You have to get creative sometimes to make weight.
But in general you take the rifle to as heavy as you can.
This right here is what a Gomer Pyle heavy assed barrel does for you.
Two shots at 600 yards from a cold clean barrel.
The fact thats its not in the middle of the gong is my problem.
Gomer Pyle heavy assed barrels also tune up quicker.
Alot quicker.
That being said I just picked up a Brux No5 for a 6.5x47 build.Thats going to be a 12lb 1000 yard light class rifle.
This should be an interesting project.
dave