Browning A Bolt, stainless synthetic, 300 Win Mag, Extractor Issue?

[Ju Wah]

Gentlemen,
Yesterday I was out sighting in this lovely firearm. I was using Winchester Power Max cartridges, in both 150 and 180 grain.
The ammo, unfired, loaded and extracted flawlessly. Once fired, it was quite difficult to extract the spent cartridge. The casing at the primer end "seemed" to be more expanded than an unfired cartridge. Shooting and accuracy was fine. Unfortunately I did not bring another brand of ammo out with me to try.
Has anyone had a similar experience with this rifle or this ammo?
Any suggestions would be greatly appreciated.
Ju Wah

 

['Boo]

Is the rifle new or used?

If used is the chamber clean and free of rust?

If new did you clean the chamber and barrel?

 

[Ju Wah]

The rifle is used and I did NOT do a thorough cleaning of the chamber, I only did a swab down the barrel. I did think of that being the issue and I will do a better job of cleaning, then try it again with the same and different ammo.
I am hoping that is the problem.
Many thanks for your input and help!