First, were the cases fired in another rifle? If not, your chamber is probably out of round or egg shaped. Almost all factory rifle chambers are out of round. Some are WAY out.

Try this: Take a case fired in your rifle. Measure just above the head with a dial caliper. Rotate a few degrees and measure again. Continue this until you've made several measurements all the way around the case. If the measurements vary more than .007", orit's more than .007" larger than industry chamber spec's, your chamber is either too far out of round, and/or not centered with the bolt and receiver.

If the above test suggests your case is coming out egg shaped, try this to confirm it: Put the case in the chamber and try to close the bolt. Note the orientation of the case. Then rotate the case in the chambera few degrees and try the bolt again. Keep doing this until you've rotated the case 360 degrees. If the chamber is out of round, eventually the bolt will close easily when you orient the case exactly as it was when it was fired.

Most bolt rifles can overcome this simply by cranking the bolt down until the round chambers. However, that short, fat WSSM case will be really hard to chamber if it's that far out. You may have to full length size or even use a small base die.