The 7mm STW was developed from the 8mm Rem Mag, so like the others have said, unless your chamber was cut with a neck-turn spec reamer, you should be just fine.I am also having trouble finding brass for my stw. I have some 8mm Rem Mag brass that a friend of mine gave me. What process do I have to go through to be able to shoot it out of my stw? I was also wondering if using the 8mm brass would effect velocity, pressure spikes, etc? If anyone has any info for me it would be much appreciated.