You might try scoring the edges of the groove with a sharp knife before cutting the dado, which may help with chipout. Make the score as deep as you can. Do this whether you use a dado set or router. Make two passes at least, no more than 1/8th deep if you use a router. Use a down spiral bit for the edges, it will cut downward which can also help with chipout. You can use a simple fluted bit that leaves a flat bottom, to clean out the middle section, or finish on the dado set. The dado set might be faster since you're making a lot of them.
If using a router, use a straight edge to run the router against, in fact, consider using two parallel straight edges set so the bit cuts the edges. If the bit to base measures less than 3 inches you will have to leave an uncut strip to support the base, or possibly have a long strip of 1/4 thick stock to place in the groove to support the router. This is why I would consider cleaning out the bulk of the groove with a dado set.
If you score the groove edges, consider putting painter tape on the cut line first, which may help avoid chipouts from whatever cutter you use. Make sure the cutter is wicked sharp.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 10-06-2016 at 11:45 AM.