There are plenty of instructables out there for doing these mods. I did this a while back with a dremel tool and a drill and drill bits a while back. I didn’t feel too worried about modifying one as it is solidly designed and only $10 with a few extra dollars in parts, such as springs, pipe tape, brass tubing, etc.
I removed all the air restrictors and then drilled all of them out to the outside diameter of the brass tubing. I sized the tubing to tightly fit on the darts. Then pressed them all in. It was an interference fit so it took a bit of work to get them in.
After the nerf gun was disassembled I put a wrap of pipe tape around the plunger and put the o-ring back on. Hopefully this should give a better seal.
I went to Ace Hardware and sized a larger spring. I also stretched it out a bit and added a couple of washers.
There was another mod to clip some tabs to be able to extend the barrel all the way out rather than just being able to put 1 dart in at a time.
All of these mods allowed it to outperform a stock Nerf Maverick Rev-6.