I had an interesting conversation with a friend of mine about .577" Enfields, original and reproduction.

He and a few others keep a record of their scores, which is generally in the high 80's and 90's at 100 yards. From reading the previous scores over 12 months, and for previous years, they noticed that they only achieved high scores in spring and autumn. In summer the scores were poor.
They concluded that it must be down to the ambient temperature. They reckon that because the rifling on the .577" Enfield is only about .003" the bullets are not setting up in the rifling because the barrel has expanded enough to stop the bullet setting up in the rifling.
Increasing the powder charge so the bullet expands into the rifling makes no difference.

Has anyone else came across this type of thing happening?