Thank you for the reply, but is there any website where I can find the hopper?

Oh, and sorry for the double post.

You can most likely find a hopper on ebay or with a quick google search (look up something along the lines of "nerf rival nemesis hopper"), but it is not worth it to spend that much money on a stock replacement part (probably more than it is to just purchase another nemesis that already includes the hopper). Don't think that the blaster you have already is useless, though. Like Meaker said, you can easily mount almost any type of large vat or tank to the top of the Nemisis in place of the stock hopper (this allows it to hold more rounds, too). I do believe that you will need to cut the vat in question for it to fit onto the blaster, but there is no shortage of written and Youtube tutorials to guide you on your way. Don't hesitate to ask questions.

I recently came across a very informational stampede modification guide while browsing the Reddit Nerf community. With Reddit's mechanics, the guide will not be seen there for long, but it is too useful to be forgotten, so I will link it here for long-term viewing and utilization. 

Disclaimer: I did NOT Write this Post. I am merely linking it here for others to use and refer to while they are modifying their blasters. All credit is due to Mortality_Nerf.

Link: https://www.reddit.c..._nerf_stampede/

I, personally, am not the most experienced with springers, springs, and pneumatic blasters in general, so I will not make a suggestion about which spring you should use.

I will, however, redirect you here: http://nerfhaven.com...pring-database/ for more information and a universal spring database made by those more experienced in this field than me.

Sorry. I am late to the thread. I have one of these blasters myself, and can confidently say it is not fit for combat. Like you said, it jams a lot. The reason for this is because the blaster is designed for the old dart tag whistlers (with the large, velcro covered tips), so the in-line magazine bananas backward to make room for the bigger heads. When you load in today’s more common streamline (I will be referring to any dart that is magazine compatible as “streamline”. This includes elites, waffles, etc.) darts, they do not sit flat in the curved magazine and enter the chamber at an angle, resulting in horrendous jamming. Using new darts with firm foam will combat this issue slightly, but will not completely defeat it. Large tipped darts will also work better, but they will not travel as far and are not as universal and cheap compared to streamlines. Even with those, the Quick 16 can still be expected to jam because the system itself is quite finicky.

This blaster is also a beast to mod, and not in a good way. Its complicated internals mean that once you take it apart, you cannot (without lots of effort) put it back together. The Quick 16 (as I believe) also rocks a reversed plunger, so performance mods are pretty much nay. These days, you can find better, easier to mod blasters that are much more reliable than the Quick 16. I personally still like this blaster because of its aesthetic appeal and its fun operation, but I would not actually run in combat with it.

This, unfortunately (if you are not mechanically inclined) most likely means you will have to open up your blaster and physically return the arm to it's home position. Somehow or another, something on the inside got screwed up, and it wont return to the home position. This may/may not be the case, but something is causing the arm to stay put (it should return on its own, as the Rapidstrike has a "three switch setup"). Other locks indeed could very well be preventing the flywheels from revving, but there are a multitude of locks inside a stock Nerf blaster that prevent kids from being harmed from improper usage. One of the locks is probably connected to the pusher arm, but there are others that also detect magazine insertion and jamdoor state (open/closed).

Your issue could be any one of these, and like I say, the best way to figure something out is to open it up. Here is a link to another post on Nerfhaven with a useful guide to all the safety locks and many useful internal pictures of the Rapidstrike for you to assess your condition.

http://nerfhaven.com...-locks-removal/

If you want to do a simple modification without breaking the bank, IMRs are a possibility (but Meaker is right, be careful not to overdraw the batteries). There are several other things you could easily do to increase the performance of your blaster without spending extra cash. For starters, you could remove all the unnecessary safety switches that hinder your blaster from working when conditions are anything but perfect, and, if you are a little bit more skilled (soldering is most likely required), you could remove the safety resistors from the motors to increase their performance without swapping them for new ones. If you really want to do some serious modding, though, the next step will be bigger motors and a LiPo battery (I suggest starting with 2S, as it gives kick, but isn't as dangerous as bigger batteries).