Beefmasters vary in size. Bulls at the biggest mabey 2500lbs and cows mabey 2100lbs. but that is very rare. most are moderately framed cattle.
Here are some links that might give you some more info.
The 1st link is the best.
if you are planning on getting beefmasters, id recommend going to Lowery Beefmasters in Sweeny, TX....if you dont mind a long drive. its about 100 miles east of Victoria, a little over 200 miles from San Antonio. they have great prices and great cattle. my brother got a heifer from there for $800 and it won 7th place beefmaster heifer at Houston