Place apples in a large pot; cover with water. Bring to a boil; reduce heat, cover, and simmer until apples are slightly tender, about 5 minutes. Crush cooked apples and simmer for 5 more minutes.

Transfer crushed apples to a sieve or cheesecloth. Let drip into a bowl until all liquid has drained, pressing gently to release all the juice. Measure 5 cups apple juice, adding water if necessary to have the exact amount. Stir sugar into juice; add butter to reduce foaming.

Bring juice mixture to a rolling boil, stirring constantly. Stir in pectin; boil for exactly 1 minute to dissolve pectin, stirring constantly. Remove from heat. Skim off excess foam with a metal spoon.

Sterilize the jars and lids in boiling water for at least 5 minutes. Ladle apple jam into the hot, sterilized jars, filling the jars to within 1/8 inch of the top. Run a knife or a thin spatula around the insides of the jars after they have been filled to remove any air bubbles. Wipe the rims of the jars with a moist paper towel to remove any food residue. Top with lids, and screw on rings.

Place a rack in the bottom of a large stockpot and fill halfway with water. Bring to a boil and lower jars into the boiling water using a holder. Leave a 2-inch space between the jars. Pour in more boiling water if necessary to bring the water level to at least 1 inch above the tops of the jars. Bring the water to a rolling boil, cover the pot, and process for 5 minutes.