if increasing the buffer weight made it feel that much more abusive.. that likely means you buffer is likely bottoming out on the receiver extension with both of them.
does that barrel have a pistol gas port or a carbine? they dont say on their website but from the pic it appears to be a carbine length.
i'm guessing that your best bet is going to be adding on an adjustable gas block and using that in conjunction with a H3 (or heavier) buffer -that will probably resolve both your rim damage issues as well as your felt recoil issues due to your buffer bottoming out.
you gotta remember, a standard a1/a2 rifle buffer is 5.2oz... and a "big bore" buffer for carbine rifle platforms can weight as much as 11oz (
http://heavybuffers.com/reference.html)
many of us are running Hoots CCWS lead slugs in our bcg's to help off set the kind of stuff you're seeing - my 450 is at a little over 9.5 oz of weight between the slug and my h2 buffer in my shared lower.
so just some thoughts to consider. i dont think messing with springs is going to be very helpful. and probably end up causing you more stress than its worth. save those for the 223/556 world where they're known adjusters.