Have a new Shield 2.0 on the way.

Only negative I've seen is it isn't the most accurate micro out there.
Anyone try a Faxon or True Precision barrel in theirs?

Any appreciable gain?

I can't speak about barrels, but I experienced a significant increase in accuracy with my Shield 9 1.0 (5,000 total rounds) when I started using Winchester NATO rounds. I keep detailed accuracy records of all my range sessions, and my accuracy with the NATO ammo was about 30% greater than it was with "ordinary" ammo. As a bonus, Win NATO costs the same as the ordinary stuff. Win NATO is loaded to +P standards, but is not labelled as such. I think the increased velocity contributes to improved accuracy. So try Win NATO and see how it goes. You might save yourself the cost of a new barrel.

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What, me worry?

My Shield accuracy increased with 124 and 147 grain ammo. A Shield is not a target gun and never will be no matter how much you spend on another barrel… I would focus on improving your trigger and shooting skills.

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S&W factory revolver armorer

Here's sort of an answer to your question.

I also have a Sig P365X with a True Precision barrel. My groups are much tighter than with the standard barrel.