I compared my 1953 and FiL's 1963 recoil spring length to my 1979 and found the 1979 to be an inch or so longer. With both the 1953 and 1963 being the same length, did the length increase as some point? Or are the two older springs worn out? Both cycle but a new spring may take more of the felt recoil away.
The older springs have taken a set. If you’re just shooting target loads you probably don’t need to replace them, just adjust the friction as necessary. From the Field Service Manual:
Replace them. That ole girl deserves fresh springs. One and done. I don’t measure any of them. If I get someone with a problem, the first thing that happens is new springs. I’ve had to many issues from worn out ones.
I will likely buy backup springs (all) as who knows what will be available in 50 years when I'm dead and my sons have my firearms. After all, Browning does not make a firing pin for my 1998 Buckmark. The design changed in the following years and only the newest style is available. The Buckmark still works but with as much use as it gets, I thought a firing pin would be good to have in spare.
I think that’s best. Buy a couple of Action Springs while you’re at it. Ranger’s and my divergent experiences show that there is no one correct answer. My use of new recoil springs led to many malfunctions with skeet loads until the new springs were broken in. My opinion is if it works properly with less oil on the tube and the friction pieces set for heavy loads, I’m OK. I just have to change that spring when I switch to buckshot.
I put new springs in every Auto 5 I buy. I do keep the old recoil springs as I have found some of the old ones to cycle some low velocity loads.