Burned thru 45 rounds of Underwood's 180gr GDHP without issue using my G20SF. Case diameter prior to firing is .421 and after is .434.

No case smiles. Accurate. Perfect functioning.

Stock barrel w/20lb RSA.

Hey, Mike, you mention 20lbs but which RSA are you using?  Wolff?  Other?  Captive or non captive? 

Last time out with my 20SF testing the PBR's not an issue either, factory RSA and Wolff RSA with the 22lb non captive spring, even trying to induce a failure, full mag, 5 rounds, 3 rounds, 2 rounds, two hands, one hand, limp grip, gangsta style.

Case expansion was @ 0.4330"-0.4340" and no smiles....I may have to load some of the known loads where smiles have been noted to see how the pistol performs with some of those.

Stainless, captive.

From Glock Store via Amazon: http://www.amazon.com/Stainless-Competition-Recoil-Spring-Glocks/dp/B00A6YEJ2A

Thanks for the update and report.