Like I said, even in this comic book movie, having him come up with the webs would be way too unrealistic. I could see him maybe reverse engineering it, but he ordered a s***-ton, and the practical uses of the stuff, I have to imagine, would keep them in production for a very long time. Oscorp doesn't know that he's using their stuff, and if they did, they'd have to weigh taking that away from him and trusting that he hasn't figured out how to make it or something similar with losing out on all of the money that they make from it in all of its other uses.
The problem is that it makes Spider-Man reliant on something he cannot reproduce himself. Which then puts him in the awkward position of maybe not having the material when needed. There's also the fact that how useful would this stuff actually be to the average consumer to warrant it's production. How do you extract the material for use? People are supposedly buying this product, yet only Parker seems to have the best way of extracting it?
I also imagine that making the shooter would be fairly mechanically challenging, especially for a 17 year old high school student. I'm not an engineer or anything, but it's a lot more than just adapting a silly string shooter.
As a mechanical engineering student, I can say that it wouldn't be too complicated to make webshooters. The issue wouldn't be the delivery method, it was the material.
At the very least, have Peter keep the spider that bit him to create more of the material himself or something. Just...don't have him have to order it off QVC.
--
TheRock ~ Slow dramatic zoom-pan. Doesn't phase the hooded man.
"You have issues." - MWC. Pot. Kettle.