Two totally different type of guns.
SMR in 45 is a little over 6 lbs.
Don't know the weight on the Colonial .58, but I'm assuming 8 or 9 lbs. I've carried the .45, it's a dream. But definitely not an elk gun.
Recoil, if you are sensitive, the 58 will be pretty significant compared to the 45.
I'm about to turn 68. I'm not sensitive to recoil, but I'm sensitive to weight.