I know, buy all the best to start with. But that's not why I'm writing this.

Those of us with experience at building our own rifles have little things that we do to improve the potential accuracy of the rifles we build.

Here's your chance to shine..........

For me, It's tapping the lower grip screw thread all the way through and installing a set screw on the trigger to take out most of the travel and creep.
Then I install a shorter grip screw to allow for the set screw. I also use a Dremel with a polishing wheel and Semi Chrome Polish to smooth
the mating surfaces of the Hammer and Trigger

I have enough conversion kits that I can match the slight irregularities in size to the rifle for a better fit. The only conversion that I've found so far that
doesn't require this is the Spike's, because it has O-Rings that seem to allow for a better fit in most any chamber / upper.
I've hand fit several M261's and that has helped them. My normal unit of choice is based on the Atchison Design.

I've never had to cut a recoil spring to tune a conversion, I don't modify the extractor, firing pin or anything else. I do polish all of the feed ramps and
have polished the bolt rails of the unplated units. The Nickle Plated and Stainless Steel Conversions seem to come with a smoother finish.

Simply changing ammunition can drastically improve accuracy.

A quality scope can make a huge difference, for me it's one with a fine cross hair.

I've found that some muzzle devices disrupt the accuracy of the 22's for whatever reason. They may work perfectly for .223 / 5.56.
Changing them out may help accuracy. The more open devices are a pretty safe bet.

I don't know that it's actually work to improve the function or accuracy but the conversions, dedicated uppers and the lowers used with them will improve overall with use. I don't know if anyone has ever worn out a 22 barrel. I've seen the groups tighten from the use of better ammo but I believe to some extent that the barrels start to break in after a few thousand rounds. This process probably peaks at some point and with regular maintenance holds at that point almost indefinitely. You may wear out the lower and the conversion or dedicated bolt. I doubt you'll ever wear out the barrel and upper receiver if you give it reasonable care.

SpecOps-13

I lap the upper receiver to barrel in all my AR builds. Not a huge improvement in accuracy, but the bbl sits in a stight line with the receiver.

Brownells tool: 080-000-182