Welcome to the forum! Quality war content doesn't get the love it deserves, so it's definitely refreshing to see someone interested in this. These are the things I would recommend, but take them with a grain of salt. Everyone has bias, and I operate cameras as part of my job, so I definitely have bias.
GoPros, avoid them. For one, the community is saturated with GoPros, and two, they suck, relative to the price vs what you get for them. GoPro put a tiny, $100 quality sensor inside a $300-500 priced camera. When your input is garbage, your output will be garbage, too. The tiny sensor just can't handle...life. Highs are washed out, mids are cripsy, lows are blocky, field is extremely deep, there is the fisheye distortion, no real zoom that I know of, no real manual control that I know of, audio is challenged, and then it records low bitrate/fragile footage that falls apart when you go to edit it. Pretty much the only good features they have are small size for easy mounting and water+shockproofing. You are wise to avoid the head mounts - the camera is proven to fly off during especially intense play, or flop down and fold over itself if you are running and come to a sudden stop.
You can hack the Mission App to hold a larger phone than it was designed for. However, I don't trust Nerf rails to hold expensive smartphones. Attachments can work their way off the rail - consider the strength of the plastic mechanism vs the weight of a phone as your blaster whips around a corner. A real camera has an even worse equation - don't mount that on a rail. Please, don't. Even if the weight is held, it will rock and creak, creating lots of shaky footage. Edit: Also, smartphones aren't a good choice for a primary camera. They have slow auto-focus and lots of motion stutter. Take an iPhone and pan very slowly...you should see it almost step across - that's bad. A camera should only stutter when you are asking it to do something it wasn't designed to handle, like 24 FPS tracking fast action. Your primary war cam needs to handle smooth panning.
Duct taping a camera to the rail actually works better. Don't do this with a nice camera, though, for good tape leaves residue.
The safest way to mount a camera is to use a universal 1/4"-20 screw and permanently affix it to the blaster. The camera screws into that and is held securely. You can trust a 1/4"-20 to hold cameras that cost as much as a house.
I am going to tell you something you won't want to hear - a balance between low budget and high quality just doesn't exist. When it comes to video cameras, you get exactly what you paid for. However, low budget and "acceptable quality" is a thing. Everyone's idea of "high quality" varies considerably, so I'm not sure what kind of look you are going for.
One thing about quality is that just because it says "FULL HD 1080p!". "TRUE 4K!", etc. does not mean that the footage will look good. Video quality is directly correlated with the sensor size, the amount of information you are able to handle coming off the sensor, the quality of the lens, how the shot was composed, and how it was encoded. 1080p is not 1080p is not 1080p, you have to look at the specs, the fine print, and visualize what those numbers are trying to tell you.
That said, you want to go for a high frame rate if you want to capture all the action, such as darts coming out of barrels and darts landing on players. 1080p60 is a good offering made by inexpensive, consumer gear. If a camera only offers 720p60, walk away. I personally recommend Panasonic V series camcorders for this, they will be in the affordable $300-700 range with broadcast quality 1080p60 and 1080p120 slow motion (interpolate to 240 FPS in-camera). Much of my best war footage was recorded with a Panasonic v750K. The bitrate is 2-5 times higher than GoPros with a vastly larger sensor. There are now versions with 4K, but I have only ever seen 4K30 and below. You want 60 FPS for fast action.
I don't recommend production cameras even if they were within your budget, as 1080p60 and above is a consumer format that they don't typically offer. Same goes for DSLRs and mirrorless, but those cameras can give you a professional film look at 1080p24 if you decide you want to tell larger stories with your events. Depending on your skillset, that direction could set your videos apart from the crowd. Most footage uploaded to Youtube is borderline unwatchable. Most cameras encode your footage as a proprietary implementation of H.264 and most people leave it like that. When they upload, Youtube transcodes it again using its own version of H.264. This is a lossy codec - it's like re-compressing an MP3, cancer for your eyes and ears. Thus, you want your master to be the highest quality possible when you go to upload it, preferably not in H.264.
Another thing to note is that you want fast SD cards. UHS-1 should be good enough. Using cards that are too slow will do strange things to your footage, as your card struggles to keep up with the sensor.
Also, consider sitting out rounds to film from the center of the field. My blaster-mounted footage varies from good to unwatchable, but my dedicated footage from sitting out is the best stuff I have. This strategy allows you to get super close-ups and unusual, forward angles on players from any team. With 1080p coming off a good sensor, you can also screenshot off the footage and create stills (rather than taking actual photos). This will give you angles and scenes that aren't possible with still photography unless you have a burst mode.
PLEASE, please, please don't load up your videos with generic effects just for the sake of it. Only add effects on an as-needed basis, to enhance something in your story. Always remember that you are telling a story with your footage, the story is the bread and butter of the video, the main purpose of watching. Raw war footage is boring, but footage loaded with dumb effects is unwatchable. If you find that no effects are necessary, put in none. Transitions, on the other hand, are sometimes necessary. There are times for straight cuts and times for fades/blurs/etc. A good exercise is to rip video from your favorite movies and mess with the effects and transitions to see how your edits affect the flow and the story. For a rich, deep sound to your footage, consider adding several audio tracks of nothing but background noise hum, matched seamlessly to the scene.
Hopefully, at least some of this was helpful. Feel free to PM about anything, no such thing as a dumb question when it comes to filming and editing.
Edited by Duxburian, 19 August 2016 - 01:28 AM.