Leica ER 3.5-14 42mm. replaced by lesser quality ERi and ER5. if you can find the ER 3.5-14 it has side focus and 30mm tube. I, too, have a 280 I built in early 1990's and I put a VX3 6x42 on it then and it still rides there today. three rams, and many elk, mulies, pronghorn and whitetails later.