Sorry I don't have a link, but a very smart guy over at the M&P Boards used this method several years ago to solve the grit problem. I think it was mp9werks. I haven't been there in quite a while.
He took a small roll pin, removed the spring from the striker block and ground the pin to fit the hole in the striker block. He then chucked it up in his Dremel Tool and polished the block on low speed.
This solved the gritty trigger problem the M&Ps were having long before Apex came out with their products.