these guns were designed to use a polymer rod....because it is flexible and makes it easier install/disassemble for field strip without a recoil plunger ala 1911 for cleaning/maintenance. The guide rod serves no other purpose other than positioning the spring at the bbl locking lug under the chamber area. It doesn't effect lockup once in battery but does center it's position in that rear most lockup-while in battery, in relation function of the spring. The after market guide rods are a gimmick. The locking lug and the bbl hood and the muzzle contact are the only positions affected during lockup. Like a 1911, which most modern pistols emulate in function, the bbl unlocks upon blow back and tilts the bbl up slightly to unlock the bbl assy(where a steel rod binds slightly on this model) and release these locking points to allow extraction and ejection followed by the next repetition of feeding. And, spring power certainly does help feed different loads of weight and or charge depending on what one feeds into the gat .....long time smith, built hardball and wadcutters for the USMC teams at Quantico for years, and I wouldn't lead yall astray on these points...cheers...