Well you guys were right, it must be the stock profile. When i shoot it on the bench the damn thing hurts, but offhand its nothing (a '*****cat' as someone said). I'm going to get the recoil pad anyway because i can't shoot for beans offhand, esp with that type of iron sight.
The funny thing is, I can take the M1 on the bench better than the .243, but the opposite is true for shooting offhand. I must have a weirdly shaped (and now, 192 M1 rounds, 40 .243 rounds and 20 shotshells later, a very well bruised) shoulder.
I also noticed one more thing but it may be in my mind. I had to remove the scope off of the .243 because it was cheap and broken, hence the iron sights. The scope mounts that my dad bought for it oh so long ago are some funny looking weaver see-through mounts that put the scope up about an inch off the top of the rifle. I found it a lot more natural feeling to put my cheek against the stock and look through the iron sights then looking through the scope when it was working. Could this be a contributing factor? Even though the rifle weighed less, the recoil didnt seem as sharp or severe.