Yes you can resize the case. If it will chamber it's ok.
Try backing off on the crimp. Make it a two step process,
seat the bullet, then crimp.
Good luck!

Did you put a nice chamfer on the inside of the case mouth?
You can pull those bullets and run the cases through again (I hate throwing out usable brass, let alone expensive new brass)

tailgunner

I bought some of the Lapua 300WM brass when it first came out. First thing I noticed is that it is thinner than any other brand so the case capacity is a little more. Second, the necks have that great lapua anneal which means they are softer than other brands. Not the head though. So, I'm gonna guess that a combination of thinner neck walls and softer neck anneal is causing the necks to partially collapse when seating bullets. Just a guess though. You might try a larger expander ball to see if less neck tension will help. Good Luck. At a buck a case you sure want to find a solution.

This IS happening when im seating the bullet. The case size is .02" shorter than the Win cases.These dies dont crimp the case at all . Now what????????????

I understand this to happen when seating the bullet not when sizeing?
Is the case being crimped? Have you measured your new cases to see if they are the same lenght as the older Winchester cases?
The seating die crimps the case as a final step in bullet seating if it is adjusted down in the press far enough. If you have the die trying to crimp the case while the bullet is still being seated it can cause the effect you`re reporting.

Hello,i recently recieved a new box unfired,unprimed Lapua brass for my 300 WM.I followed the same resizing and preparing procedure for the Lapua brass as i have for the Win brass that has four reloads through them.Upon seating bullets,i noticed a slight bulge at the shoulder,only 10% is bulging,not the complete diameter.There are no dimples or gouges,just a bulge big enough that it wouldnt chamber. I used the same measurements and amount of lube as i have on my 4 times fired brass. My die set up is an RCBS FL. What is causing this? Thanks

Yes,i chamfered them before. I treated them as if they were once fired. Are you sure i can re-use them if i run them through the re-size without ruining the die? Thanks