Substitute pig trotter for powdered gelatine in an aspic I'm intending to make a raised game pie, which involves making aspic from the stock.

The recipe says to make 1 pint of stock from the game bones and trimmings, herbs, root vegetables, and to whisk in a 0.4oz sachet of powdered gelatine before chilling the stock.

However I'm aware that the traditional method of producing savoury jelly for pies is to use pig's trotters.

How many pig's trotters should I use to produce 1 pint of aspic for a pie? Is there anything I should know that I might not have thought of?
I think the biggest problem is your not going to be able to judge how much gelatin any given pigs foot is going to produce, hence the recipe calling for extracted gelatin to sort of foolproof the recipe. But if your going to try and make it with just the pig's feet I would suggest having a look at this recipe here for "Trotter gear" 

http://www.seriouseats.com/recipes/2011/03/recipe-for-a-healthy-jar-of-trotter-gear.html

Anything coming from Fergus Henderson is going to be awesome. It recommends 6 feet and that recipe produces a pot's worth of stock so I think that will suffice for you.