http://www.ar15.com/forums/topic.htm...f=118&t=492084

boils down to. no, you really dont need them. but, you may have to have them now. does your upper have cuts, where the feed ramps go? if so, then you need to buy a barrel with m4 feedramps. if it doesnt, then you can buy either, with m4 feedramps or without. clear as mud right? its simple really. an m4 feedramp equipped upper receiver needs an m4 feedramp barrel/extension. a regular upper can use either...