Edited because I remembered how to activate the links.
For all of Colt's hyped features of the M4, they only have one patent that I know of, and that is for the handguards.
[url]http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/search-adv.htm&r=60&p=2&f=G&l=50&d=ptxt&S1=colt.ASNM.&OS=an/colt&RS=AN/colt[/url]
The only other Ar-15 related patents I could find assigned to Colt are the following
[url]http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/search-adv.htm&r=62&p=2&f=G&l=50&d=ptxt&S1=colt.ASNM.&OS=an/colt&RS=AN/colt[/url]
[url]http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/search-adv.htm&r=81&p=2&f=G&l=50&d=ptxt&S1=colt.ASNM.&OS=an/colt&RS=AN/colt[/url]
[url]http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/search-adv.htm&r=103&p=3&f=G&l=50&d=ptxt&S1=colt.ASNM.&OS=an/colt&RS=AN/colt[/url]
[url]http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/search-adv.htm&r=207&p=5&f=G&l=50&d=ptxt&S1=colt.ASNM.&OS=an/colt&RS=AN/colt[/url]
Feed ramps, heavy buffers, extractor D-rings, stocks, bolts, etc. are not and never were covered by any patents. This is why Colt had to go to court claiming irresponsible distribution of the Technical Data Package to barter with the government for a sole source deal on the M4.
I recently wondered about the M4 ramps when, last week, I received a price list from the Canadian distributor of Armalite stuff, that claimed to have M4 ramped uppers. I knew the ramps weren't patented, so I was wondering why nobody else had been doing them up to now. Certainly the 2002 price list didn't include M4 ramped parts. I would guess that Bushmaster, Armalite et al have only started producing these in the last 4-6 months.