…which should I order for my RRA Elite CAR A4? Thank you. 
Tom
Either one will work fine but IIRC Brownells doesn’t charge extra for the CS springs so I’d get those!
CS is the better spring. It is much more resistant to compression problems.
The CS spring will, however, rust more easily. Since I don’t make it a habit to lube the insides of the mag, I have stuck with stainless springs.
Actually high grade CS (like what ISMI uses) has the same rust fighting abilities that SS does.
C4
I would go with CS Springs.
CS will usually develop a thin rust, but it’s practically inconsequential.
Which obviously isn’t used in the Cproducts ones.
I’ve never had a ss spring fail and never had one rust. The mag body has always gone first.
If worried about rust you could always put a very, very, very light coat of oil on them and have no worries.
This is correct. They do use lower grade CS springs. High end CS springs are very pricey (which is why no manufacturer uses them).
I have changed out several springs in mags that weren’t providing enough tension. They were many years old though.
C4