DBT ... there is a much better and cheaper way to accomplish what you want to do .... Get a PAST Shield!!! They cost $20-something. I got the $10 cheapy Winchester version .... it works wonders!! I only take it when I'm shooting the 300 and 7mm Roys. One range session I put 70 rounds down range with these two rifles (40 in the 300 and 30 in the 7mm) wearing my pad and a t-shirt. My shoulder felt like it would after about 10 7mm shots or 2-3 outta the 300, not sore, just a little tender.
If this little cheapy pad can tame my magnums, I would imagine you could shoot the 308 all day and still be smiling <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />. w/o the brake or Hg added to the stock!
Do yourself a favor ... don't mess with your rifles until you tried this ... I'm bettin' you'll be happy you did!
