The obvious method, and the method used by the big boys is the small explosive charge inserted into a blood filled condom, and then detonated by a remote control. The first time I really understood how this worked was when I was a wee child watching Fangoria's Scream Greats Video Magazine on Tom Savini. As a matter of fact I think it was one of only two video magazines they did. I actually found the opening to that video on YouTube. God this brings back memories.
I watched this so many times when I was a kid. Had every special effect memorized, went out and copied everything I saw Savini do from this video. As a matter of fact I still have my crappy VHS copy somewhere. But it was this video that really got me started on trying to figure out how to do my own bullet hits. And back then safety was a side thought. I did what so many of us did. Got a ziplock bag (cuz I couldn't get condoms at such a young age), made my own fake blood (out of cough medicine, pretty expensive blood actually), filled the bag, wired a battery to a firecracker, and shoved the firecracker in the bag.
I heard so many stories about people blowing themselves up, so I was pretty frightened as I stuck the wired bag to the fence in my backyard/testing area. I touched the other end of the wire to the battery. I thought for sure it was going to explode, but nothing happened. Turned out that the ziplock bag was too thick, the blood was too much, and the firecracker exploded with no effect because of it all. But I was convinced that this was the way to go.
Here's a clip, from back in the day, of Savini on Late Night with David Letterman.
I actually remember watching that when it first aired.
The explosive charge is all well and good if you've got everything prepared properly and had all your safety measures in hand, but when your a kid or an amateur moviemaker with no money, using any type of explosive is a risk not worth taking. I could have very easily blown an eye out handling a battery attached to a firecracker, any type of explosive is a risk.
Here's a video displaying one of the more riskier methods. I don't think I would risk doing it this way. Explosives, no matter how small the amount, are always a safety concern. I mean honestly, in this video, does this guy really want to put his life in the hands of a chopping board?
So doing the firecracker bit was a big turn off, on top of the fact that sometimes it just didn't work properly. There had to be a better way for no-budget indies. Once again, the internet comes through. In the late 90's the popular method became compressed gas, or compressed air. Genius. And one of the first places to put up a detailed tutorial on the matter is still up today, EXPOSURE.
The Complete EEFIT'S Guide To Filmmaking shows in detail how to accomplish a bullet hit with am pump-up sprayer and a garden hose. Check out EXPOSURE's Tutorial on Blood Hits here.
This method is the one widely used by many indies today. Here's Indy Mogul's Backyard FX spin on the same idea.
A few years back I did some test shots using the same method. Except I used an actual air compressor, which came in quite handy. I rigged up a small tube of blood to an old shirt that my wife was wearing, and then rolled camera as I preceeded to show my wife/zombie getting shot in the stomach. Why you'd shoot a Zombie getting shot in the stomach, I do not know. It came out quite well. Unfortunately she doesn't want anyone ever to see this footage do to her unfortunate hair style. LOL.
Nowadays I have my trusty pump garden sprayer (thank you Tabije.) The only real pain is having to pump the sprayer up, which is actually a nice little workout for your arms. Thankfully there are new and bloodier ways to create this effect sans air.
Here's RawrFilms/GageFX version of the pull string method first documented by Stu Maschwitz's The Guide.
I have yet to try this method, but certainly will on Monster Cops.
But that's not the only method out there. Found this video on YouTube, and I think it's the simplest and not too uneffective method out there. Embedding is disabled, sorry.
Ah yes Egg Shells. I think it's a great idea. I'll certainly be using all of the above, literally and can't wait to get started. Combined with some of my own ideas on creating bullet hits to the head, and some (not too much) CG work. I plan on making all of the Monster Cops bullet hits effective within the confines of the plot. After all, the effects are just one of the tools in storytelling, as it should be. The effects should never be the star of the movie, if it is then that's the first sign your watching a movie with no plot and all style. Which I think people have had enough of.
Still nothing like a good blood explosion. Remember though, safety first, plot first. Don't get killed for style's sake. Stay alive and tell a story.