Place 1 cup of the raspberries in a 6- to 8-quart heavy pot. Use a potato masher to crush berries. Continue adding raspberries and crushing until you have 5 cups crushed berries. In a small bowl stir together 1/4 cup of the sugar, the allspice, and the pectin. Stir into mashed berries.
Bring berry mixture to a full rolling boil, stirring constantly. Stir in the remaining 3 3/4 cups sugar. Return to a full rolling boil, stirring constantly. Boil hard 1 minute, stirring constantly. Remove from heat. Quickly skim off any foam with a metal spoon. Stir in pomegranate seeds.
Ladle hot jam into hot, sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.
Process filled jars in a boiling-water canner 10 minutes (start timing when water returns to boiling). Remove jars from canner; cool on wire racks.