When I've experienced this problem it's generally because I have failed to set up the sizing die so it bumps the shoulder. Make sure the shell holder makes contact with the press ram. If this is your problem it will cure it. Best wishes.

Cal - Montreal

First off Thanks for all the replys.
I can close the bolt on factory ammo like nothing.
but even once fired factory ammo going back in is tough.
i have tried full lenght sizing with the shell holder right tight with the die in the press still tight.I will go to the range today if i get time and fire a factory round and try the marking pen trick to see if that is the problem.
If it is a misalignd chamber i hope winchester will replace it free of charge as this rifle is only a month old.
I will let you know what i find.
Thanks again.
CdnWalleye

I had a similar problem with my 300WSM, I had to remove some material from the top of the shell holder in order to get the re-sizing die to bump the shoulder on the case enough to give easy chambering.

IF a fired case is hard to get back into the chamber before it has been touched by a die, something is wrong! It should go back in very easily!

The WSM series is apparently loaded to somewhat higher pressures than most rounds, and this could be causing problems in your particular gun. However, if you are not experiencing difficult extraction it is unlikely that high pressure is the cause of your problem. As others have said, if a fired and unsized case will not re-enter the chamber readily, there's likely a problem with the chamber.