Upgrades I would recommend are a 150% recoil spring. A 190% hammer spring and high flow valves in your mags should help give you some extra velocity. A warning though - the hammer spring requires disassembly of the entire gun, and can be pretty complicated. To me, that's best left to a gun doctor. Recoil spring and valves are easy to change.
Those are pretty much the only upgrades you'll find for it. I've been looking for a tightbore barrel for mine for some time, but no luck as of yet.
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