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Ok great thank you both for your info!! I do not belive this has a CS marked stock. I believe it is standard a2. This issue with this gun is colt cannot letter it due to them having no info of it in their systems.
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My carbine as well as the majority of the Sporter series (1991-1994) had the steel sear blocks on the lower receiver.
Yours have it too because I could see the blind pin above your selector.
My carbine have no CS mark on the stock but it have a shorter stock which I compared with my other Sporter Target rifle with a standard A2 stock.
You could compare your buttstock length if you have a standard A2 rifle, or someone you know might have one and compare it side by side.
If not you could measure the LOP (Length Of Pull) from the front of the trigger to the rear end of the stock, A1 LOP are 12.875" while the A2 LOP are 13.5" (difference of 0.625" or 5/8").
I used my Sporter Lightweight carbine for about 13 years and I never had any problems, it was very reliable and I mostly use it for home defense which I used it on the 1992 Los Angeles riots when I was living there at that time.
The only features that I dislike personally were the steel sear block, half moon type bolt carrier, and the large diameter offset pivot pin.
About that same time in '91 I also bought a Colt model 6551 Sporter Target 20" barrel rifle and I was lucky it didn't have the steel sear block, I sold it also for a nice profit during the ban in 2001.
Currently I have 4 Colt carbines and a rifle, 6721 AR-15A3 Tactical Carbine (new old stock made in 2002 bought it in 2005), another 6721 carbine made & bought in 2010, SP6920 marked Sporter M4 Carbine 2011 model, and a Match Target HBAR lower made during the ban with a new never issued M-16A2 Colt upper half.
The Colt factory probably doesn't have the personnel to look at their manufacturing records and they're just using the excuse of your serial number was not in their system.