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Old October 30th, 2007, 13:19   #5
ILLusion
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Join Date: Jun 2002
Location: Toronto
The entire front end as well as the upper receiver is different between the standard M4 and the S-System.

It'd be easier to just pick up an SIR to install on your M4. Combine it with an A.R.M.S. Standalone flip up rear sight (or a replica), and you'll have a very close S-System replica that's built better.
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