Congrats, you have a very nice Colt rifle, nice new in box find.

I've been a very long time Colt user since 1971, started with my very first AR-15 SP1 sporter and had five other pre ban different Colt models.

I have currently two a 6721 A3 Tactical Carbine and a MT6601 Match Target HBAR lower with Colt M16A2 upper half.

The two closest Colt models I've had to yours was the older than yours model HBAR which was the R6600 AR-15A2 HBAR Sporter, mine had a bayonet lug, A1 type lower receiver without mag fence around the mag release and no sear block.

The other one was the government (same profile as M16A2) lighter barrel profile than yours which I got in '91, no bayonet lug, it had mag fence around the mag release and no sear block model R6551 Sporter Target.

I used my HBAR mainly in the mid '80s DCM/ CMP rifle matches and I did well with just a stock out of the box rifle.

For self defence weapon I prefer to use carbines like my 16" 6721 because it's easier to swing and move around with also I'm not going to shoot more than 100 yards with it, the most common self defense range is about 50 yards or less.

No problems what so ever with all my previous and current Colt rifles and carbines, if there's going to be another SHTF like I went though back in the '92 L.A. riots when I was living there at the time, I would grab my Colt carbine first like I did back then.