I also use just a sledge and have a smaller leather mallet which is nice and or course have made on site commanders for those times the sledges were left in the shop. As much as possible strike the unseen faces and use a block as a pad. I also look for knots, you are pounding on end grain and it isn't as bruising as hitting the flat grain. One would also be cautious of hitting the ends of tenons, the relish on the peg holes can have reverse failure which is a sad thing. The tenon can be mushroomed which will call for new chamfers. Tim