So last year I built a low weight ar 15, using a smoke composites carbon fiber stock. I initially chose the 'short pull' and after installing it, taking to the range a few times, I just didn't like how short it was.
Mind you, it was a YEAR later when I decide it's too short.
I email smoke composites and ask if I could send some pics in of my barely used stock, and could i upgrade for a longer stock, how much would it cost, etc.
They email back, no that's fine. we'll just send you a newer, longer one. Just send back the used shorter stock when you get the package.
A few days later a package arrives with a brand new stock, I switch them out and I love it.
Mind you a few items for Smoke:
I offered to pay for the upgrade, they did this all for free, shipping, swap, etc.
They never really KNEW I had a stock in the first place. They trusted me.
So a year afterwards, I 'change my mind' and they let me switch parts for free. That is customer service.
If you are looking for a lightweight stock or handguard I strongly suggest you check them out
http://www.smokecomposites.com/stocksThey also do custom work. If you have any qualms about carbon fiber I can assure you the stock is hella strong (that's a technical term) and the finish work is excellent.