Real pies are expensive enough that no sane director is going to want enough around to cover more than one take.
As to weight – pick a pie up. Assuming an aluminum disposeable pie pan, you’re still talking a minimum of a pound or so, and that’s if it’s a cream pie. Use a fruit pie, and we’re looking at a minimum of two or three pounds.
I guarantee if I hit you hard enough to guarantee any degree of accuracy with ANY three pound object, you are going to find it a bit of a shock, particularly since you know it’s coming and have closed your eyes. Disorienting at best, and injurious at worst; I’ve seen several people suffer nosebleeds, and stunning effects weren’t unheard of. Even had one guy accidentally inhale part of a pie, and wasn’t THAT fun…
My theatre group experimented with this in high school. Whipped cream sprayed into pie tins was about the only way we could make it work, and even then, we had to be careful slamming them into each other’s faces; when you’re onstage and pumped full of adrenaline, you can coldcock someone without ever meaning to, or realizing you’re doing it.
We didn’t long use shaving cream pies. They’re cheaper, but the risk of irritating the target’s eyes is a big one, and the last thing you want is to be onstage in front of a live audience, totally blind, with soap in your eyes. We used whipped cream, and held an extra fundraiser that year to deal with it.
THROWING the pie compounds the problem; hurling a real pie with any degree of accuracy is going to run a risk of injuring the target. Unfortunately, whipped-cream combat pies (yes, that’s what we called them) are too light to throw with any degree of accuracy beyond a few feet. After some experimentation, we settled on choco-whip pies for ranged effects; they delivered nicely, were about as aerodynamic as you could expect of a pie, and had enough heft to hurl, without being as heavy as real pies.
A variant on this theme allowed for a graham cracker crust, if the situation calls for the target to stand there, stunned,while the thing drips off him (whipped cream pies don’t drip quickly at all, and may well simply stick there on the target’s head, pan and all; choco-whip pies, due to their semicolloidal nature, tend to fall off fairly quickly, leaving the victim besplattered, but quickly recognizable. You want the classic effect of chunks of pie falling off your stunned victim gradually, you want choco-whip with graham cracker crust. Works in color, or black and white.)
The WHIPPED CREAM PIE was simple; simply obtain a can of spray whip, or a tub of Cool Whip, or any suitable substitute, and dish it into a disposeable aluminum pie pan. Be careful about hot lights and suchlike; it’ll melt!
The CHOCO-WHIP PIE is somewhat more complex, but actually cheaper; obtain one package of Instant Pudding mix, and some milk, and prepare according to the directions, but make a point of whipping it more or less continuously with an electric mixer; a large amount of air gets into the pudding, and eventually, you wind up with a kind of thick, heavy pudding/cream stuff; dish into disposeable pie pans. One box will make three pies, easy, if you’ve done it right. Somewhat more resistant to melting under the lights than whipped cream, too. We used chocolate pudding, but any flavor or color would work, theoretically.
The VARIANT CHOCO-PIE was prepared the same way, but dished into an ordinary graham cracker pie crust before use.
Another trick: money can be saved by using paper plates instead of aluminum pie pans, and the plates are actually slightly safer. Get a can of silver spray paint, and spray the BACKS ONLY of the plates several hours before use; do NOT get any paint in the part where the pie will go! Use only on stage and in long shots, where the audience won’t notice the difference. Also useful when the performers intend to attack confederates in the audience; if a pie gets out of control, the damage it can do is minimal (although whipped cream, rather than choco-whip, is strongly recommended under the circumstances!)