I recently picked up a poly tech M14 and am now in the process of buying things for it. Yesterday I was at my local gun show and picked up a walnut stock with the correct stamps, but the handguard it came with was vented. Was the vented handguard an issued item or is it a modification someone else did? the slots are very uniform in the fiberglass and look factory but I am a new to the m14 platform and did not know if this was a USGI part. Any help on this handguard would help