Brick slip pointing mortars are usually just sand and cement mortar sometimes with an additional part of lime. The sand is usually graded below 2mm so that they can be used in mortar piping guns and bags.
Sand and cement mortar (Portland Cement mortar) is typically 1 part Portland cement and 6 parts aggregate (fine sand) for a mid-to-soft pointing mortar. The more cement you add the harder it becomes.