Good afternoon, new member here and also a new owner of a M&P15OR!! A couple questions: what is meant by a "high profile gas block" I do not think this applies to me or does it, trying to find some sights and a little confused on what type. Can I mount both front and rear sights on the rail or will they be to close, if to close, then for the front sight, just get one to mount on gas block, not one for high profile gas block? Not looking to spend a ton on sights, just want to get started firing! Thanks for the replies, Ricky