What cal are you putting the muscle break on. I have one for my Edge build, and I hope it will tame the recoil down to 308 levels with a 300gr pill. The rifle will weigh in around 13lbs.
I have Jims 3port brake on my 300 win Sendero. I would say the recoil is slightly more than a 243. In talking with Jim the muscle brake is considerably more efficient.
Over the past few months the only gun I have shot has been my Sendero. I took my Ithaca 30-06 deer rifle out the other day to do some load development. It is a light gun with a plastic butt plate. I started shooting with the Sendero - nice + relaxed off of sand bags - just a gentle push. I made the mistake of holding the 30-06 the same way - pulled the trigger - oh shxx that hurt - I now have a bruise the size of a fifty cent piece. Thats what you get for not paying attention.