Should be 1901 to 1903. It started at 12500 in 1901 and ended at 125600 in 1903 which might narrow it down a little. Jeffery never actually made guns but commissioned them from the trade. Look for other numbers or hidden trade marks or small worker's initials and it might be a clue to the actual maker. If you can post a photo that may also give some clues. None the less he only commissioned stuff from the better makers. Lagopus.....