The following rather lengthy article is my account of a similar effort to improve a marginal Springfield MilSpec by replacing the defective factory barrel with their Trophy Match/TRP barrel. Hope it is informative and helpful to your situation.
I picked up a new Mil-Spec in January.
Range conditions were not ideal for the first outing, but I was anxious to shoot. All shooting was done at 25 yards, and the groups were shot while seated on a cold, wet bench and shooting over the range bag. Yee-Haw. I started with Wolf hardball, standing on my hind legs and blasting away at an empty cartridge box on the snowy berm. Point of impact was a little high left, so I switched over to a paper target that someone had shot with a .22 & left hanging on the stand. 5 rounds of Wolf went into 4 inches, about 4” out at 11 o’clock. I noticed I was fighting the creepy trigger, and determined to concentrate on the sights and just press it off.
I switched over to my 200 grain SWC reload, and a fresh target. 5 shots went into 3 1/2 “, with three of them under 2”, and it was grouping closer to the sights:
Next up was Federal 230 HydraShok, which produced a 3”, 5-round group:
Now, you’re not gonna take Camp Perry by storm shooting like this- but I have shot guns that shot worse. By this time there were about 22 rounds of everything left, so I loaded the factory mag with every round different than the one below it, using all loads listed above. Then I turned and hosed the rounds into the berm, as fast as possible. I repeated this three times, and the MilSpec ran like clockwork with the mixed loads.