Answer
Wa `alaykum as-Salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question and your commitment to Islam’s rulings regarding halal meat.
Generally speaking, kosher is halal provided that cutting the veins of the animal is actually done.
As for the machine slaughter, it is like the hand knife. It should not be painful to the animal.
Responding to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
True kosher is equally permissible. But a Muslim in America should be careful about kosher for two points:
1) Some kosher is not true because it was in the news sometimes ago that a Rabbi in New York blessed a whole slaughter house and claimed it kosher without cutting actually the veins of each animal.
2) Some businesses in America donate to the occupying power in Palestine. It is haram to support such businesses.
Machine slaughter is as halal as hand knife. Hand knife, after all, is a machine too but it is the machine of the past. You cannot find a hadith on this but you need a Hadith to prevent it.
If it is easier for the worker and the animal, it falls under the general Hadith that the Prophet (peace be on him) always preferred what is easier. Besides, the OIC Fiqh Academy discussed this Issue in its meeting in November 2013 and did not make any objection to using the machine although it stressed the idea of cutting the veins and draining the blood out.
Allah Almighty knows best.