You need to determine what front site you have one your rifle. There are two or three different heights. If yours has the F stamp on it then you should be ok. If not you will need to research different height sights that will work for you.
A1 and A2 models have a different height on their sights due to the fixed carry handle. When they went to the flat top and removable carry handle they went to a different height front sight and and are stamped with a F on them. I cant remember off the top of my head what the height difference is, I can dig the book out and look it up. Or some of the more knowledgabe members here will prob be along and clarify it a little better for you.
As is mentioned, the Magpul MBUS is intended for use with the the standard A2 "F" marked front sight without any modifications. Should you have a non-F-marked front sight, there are extended front sight posts available to make the height adjustment. The extended front sight posts don't cost much.
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