Six Inch match grade hunting barrel. I would be using Underwood ammo with her and some hard cast. They offer 20 lbs, 22, 24 or stock 17 lbs springs. Also stainless guide rod or tungsten (for 2x the cash of stainless) What do the 10mm guru's advise? For the 6" version and pretty hot ammo I was guessing 22 lbs, but maybe the 20 is enough.? PS I've been waiting 4 months for a lone wolf, I can't wan't to increase my killing power any longer. I've a stock weight stainless guide rod already if that is enough.