Not sure how many shots you fired, but your barrel starts to heat up after a while and your groups will start to open. If I were you, I'd wait between shots to let your barrel cool down. I usually bring a .22 along with so I can plink while my targeted gun barrel is cooling off.

Also, psychologically, the negative stimulus of the bruiser going BOOM!... and shoulder THUMP!... may be influencing your pucker factor too. LOL!

iSnipe