12 is provided with an integral upper rail portion 18 and a plurality of modular rail portions 20 in one embodiment the modular rail portions 20 can have varying lengths or sizes to provide numerous configurations and or variations the hand guard or upper receiver is configured to have a plurality of integral features for removably receiving and engaging the modular rail portions 20 such that user desired configurations can be provided integrally formed on the left side and right side e g nine o 39 clock and three o 39 clock positions of the hand guard of the upper receiver are a plurality of features 22 features 22 are configured to releasably receive appropriately shaped features 24 of the modular rail portions 20 as illustrated in the attached figs a plurality of channel openings 26 are provided wherein each of the plurality of channel openings 26 is configured to allow the features 24 of the modular rail portion 20 to be inserted into and out of channel openings 26 in a vertical direction illustrated by arrows 28 as illustrated each of the plurality of channel openings 26 are configured to be appropriately distanced apart from each other such that the distance between each of the channel openings corresponds to the distance between each of the features 24 of the modular rail portion 20.