I shoot JSB Exact Heavy's in .177 and have emptied a fair number of tins through the years. While I do not weigh the pellets, there has always been good consistency in how the pellets seat in the breach. Unitil I opened a tin from batch 15560014... Never had I experienced such a random varience in pellet seating - it ranges from tight to loose and everything in between. Even a wash in luke warm water with a drop of washing liquid and a good rinse has not made any improvements. This is the first tin of JSB pellets I feel like chucking into a corner and opening a new tin (from a different batch!) with hopefully better consistency.
Before you purchase JSB Exact Heavy's .177, keep a look out for batch 15560014 and stay away!