300 BRM Brass (100) - Brass for 300 Bench Rest Magnum. All of our brass is made from 30-30 bulk brass. It is formed and trimmed to length. You should expect to full length size it and some minor trimming might be in order. 7-30 and .375 and the BRMs are a little shorter than spec as we widen out the original 30-30 enough that it draws brass from the length. But, they are completely functional and accurate at the length provided.