Hornady Custom Modified Case question

[Winny94]

I have a very tight chamber on my 260, so i was planning on sending in a couple pieces of brass to have them make a Modified case to my chamber. The question i have is: I plan to shoot my 'best' loads with lapua brass, but I haven't loaded any yet, ive been shooting Prime. Can I send the Prime brass for the Modified case and use those dimensions and apply it when I load the Lapua cases, or would I be better off loading Lapua cased loads and using those fired cases for the modified case?

thanks

 

[padom]

Chamber a piece of virgin Lapua, if it chambers send it to Copper Creek and have them drill the back so it fits on your overall length gauge. You dont do this for every different case manufacturer you use....