I could be out in left field on this one, but it's my understanding that manufacturers load to a velocity standard, not a pressure standard. They don't concern themselves with pressure as long as they're within SAAMI standards. I'm sure the Winlites are all "lite" and well under the SAAMI max of 11,500 psi for the 12ga, but I'm not so sure that they're always loaded with the same powder--as long as the velocity stays the same. Perhaps someone who has pressure tested the same factory loads from different batches could comment.
