Wow, that suprises me, I have all 3 mags and when I looked at carbs, summit was about 150 bucks cheaper than SD, although i never looked at bare blocks in either book, summit is deffinetly cheaper on most things. Is the block you looked at, Part # 10066034? this block is 579.95 in SD, I could not find it in jegs or summit but I trust your word.