Your Colt 6920 is more than acceptable the way it is – it came with a sling and sights, and this is an excellent place to start. Get plenty of ammo and magazines.
You have already avoided many of the reliability concerns by purchasing a carbine that complies with the Technical Data Program (TDP). Of course, there’s no guarantee yours isn’t a lemon until you actually start shooting it – which you should always do with a new gun and all the magazines you use with it. Knowing what works before you attend a good carbine course will save you much aggravation – or hone your malfunction clearing skills. Save your money on the good trainers and equipment, when the time comes.
To repeat the best advice: First get your mindset right, which is to spend your money on GOOD training. Once you have a better understanding as to the system’s capabilities (as well as your own), you will have some experience to help guide you. Of course, we encourage you to learn from others who know (that’s the most economical way to go) and SME’s and Industry Professionals have better advice than others.
The AR platform has seen decades of service just as you have it – and it has performed with aplomb, so don’t worry about the accessories just yet. If you want an inexpensive but effective light mount NOW – MI makes a decent front sight base rail, and you can mount a Surefire G2 Nitrolon for weight savings and simplicity. Understand the “best” light on your rifle won’t help a lack of situational awareness…
A good instructor, for example, might teach how to use a handheld with carbine, should your light die on you – as opposed to hawking a specific product. Gadgets have a tendency to fail when you need them most, so KISS…
In the old days, we used to use plumber’s tape and other ugly methods to mount SL20’s onto subguns and shotties, and we were still cool!
Granted, today’s 1913 rails are cleaner and more precise – but they are STILL really JUST about attaching things that most of us may WANT, but don’t really need. (IMHO, accessorizing first is more like playing Barbie, whereas enhancements after training is more like LEGO!
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Economically, Viking Tactics offers a practical, lightweight mount and G2 light combo for about $60 – which translates to about 150-200 rounds of ammo! We want “trigger” time – not “sit in the safe” time.
There are plenty of folks out there who want your money – so spend wisely, whether for training or gadgets. Most folks here want to help you protect your investment…
Just my $.02 – and about all it’s worth…