I have a '76 model Colt 70/80 Government with the same problem.
Mine is 100% original and belong to family members that most likely never shot it for at least 25 years prior to my receiving it.
I checked online and it seems like around $5.99 for a new Colt recoil spring.
Should I try a new 16# recoil spring?
I get the same 1/4 to 1/3 of the brass flattened out on my spent brass. I do reload mine on a Dillon 550 with Dillon dies and no new problems other than more flattened brass, no more than from factory brass though.
Thanks Everyone for all the info received on this website, I don't post much but read a lot.
Thanks