1S is a medium sporter usually with heavier calibers, 45-70 mainly. It has a shorter, thicker barrel at 22". 1A is a light sporter usually in calibers like .243, .270, 30-06. It has a thinner, longer barrel at 24". Yes, they do weigh in at about the same, around 7.25lbs. there is no hard and fast rules though when it comes to No. 1's. There are medium sporter 1S's in .218Bee. I believe you could also get .300WinMag in 1A, 1B, 1V and 1S at one time or another. Whatever you find it in matters not. If you like it, buy it. No. 1's have never let me down. I've never sold one and never will.