Ok so I went in to my local store with the intention of buying a kjw gbb 615 because it's c02 compatible. Due to wanting zero issues with part replacement the owner talked me into a tm hi capa 5.1 government model.ok now that that's out of the way here's what I want to do.I would love a smaller grip or even a shorter trigger,from the bottom of my palm to the tip of my middle finger is roughly 6.5in and the reach to the trigger is uncomfortable so that will be the first thing to go.im looking for something preferably metal. Second would likely be the slide and frame again preferably aluminum and love the look of the usp match set,if I could find something similar I would be stoked. As far as performance I'm looking to be right on the 350fps point if I can beef it up enough to be 350 with green gas and like 380 with c02 that would be a dream.i am fairly new to airsoft upgrades in general but any recommendations would be greatly appreciated.if you can post a link or part number to suggestions to make it easier I would be forever in your debt. I typically play private games so rules are a bit lax but I would love to be able to get out to an actual field which is why I was hoping to find a way to hit diff fps points by simply switching fuel types...obviously after upgrades. Thanks again.

Based on what you are describing, sounds like the HiCapa doesn't really fit your hand.

Rather than modify it, risk damaging it and/or losing all resale value, you might want to consider selling it and replacing it with a TM1911 variant like the M1911a1 or MEU. There are a number of manufacturers who make similar guns, WETech, KJW, KWA all make decent M1911s. The HiCapa is essentially an M1911 with a double-stack frame installed.

If you really want to mod the HiCapa you should be able to find a shorter trigger for it (I'd look for an M1911a1 trigger). They make metal slides for the HiCapa, as well as the M1911s I mentioned before.

For reliability I would recommend a hammer spring; my HiCapa and other M1911s tend to have trouble blasting the valve in hot weather. The hammer spring upgrade fixed that. You can also get a modified recoil spring to make the slide cycle faster, but it won't lock open on the last shot. Improved hop bucking and a titebore barrel can also make a difference with a pistol.

Increasing FPS with gas guns is kinda wonky. Instead I'd focus on increasing range and accuracy - a new hop bucking and barrel will get you there.