THE TECHNOID SAYS IT'S TOO DARN HOT..... It is a fact- shells kick more
in summer. Back in his salad days, the Technoid ran across a few cases
of International Skeet shells from Poland marketed by the notorious, but
aptly named, Pawam Pionki. They came packed in wood and fiberboard
crates. They kicked like mules. This was understandable since the horse
hair wads also made them smell like equine marshmallows in your local
auto de fe. Aside from maximum amounts of recoil and odor, their main
trait was sensitivity to temperature. The hotter the weather got, the
hotter they got. In winter they produced the odd blooper. In the
summer, if left out in the sun, split case heads were the rule. Some of
this might have been Poland's cold war attempt to destabilize the West,
but most of it was due to the due fact that the chosen powder/wadding
combination was extremely temperature sensitive.

Today's modern powders, especially those used in hunting loads, are
remarkably stable. However, there still is a difference between hot and
cold weather performance. Rifle reloaders are particularly aware of
increased pressures due to hot weather, but it affects shotshells too.
As speed and potency increase with heat, so does recoil. This is more
noticeable due to the lighter, less padded clothing worn in hot weather.
The end result is that shells do indeed kick more when it is hot. Many
savvy reloaders drop their powder charges by a grain or so in summer to
keep performance and recoil consistent.