When you can’t decide between Ruger Mini-14 models with either stainless steel or blued alloy receivers, you shouldn’t worry much because it’s a pretty marginal difference. Stainless steel is slightly more corrosion-resistant than blued alloy steel, but that doesn’t mean they’re invincible. Rust and discoloration can easily happen if you keep the rifle in moist and humid places, so if you live in such an area, your best bet are rifles with a stainless steel receiver. It’s a small price to pay for longevity.