Umarex FX Notos .25cal Build

Hello there! First time posting and first airgun build. My old man gave me his old Umarex Gauntlet that he had about every Hajimoto part installed in. Now I'm over here spending stupid money on a build that I know he is just going to SMH at. Lol The gauntlet didn't have anything else for me to mess with so I have started a .25 Notos build. The whole reason I started this was because I came across a cheap FX barrel liner that USPS still hasn't managed to deliver to me while the rest of the gun has been modded and ready to go.

I am looking for any advice they may help me push the rifle as far as I can. I have the c88 500mm .25 conversion kit along with his 4mm valve body. I have ported the transfer port to just under 5mm. Not sure how people are getting the full 5mm without kissing the threads of the hole you have to drill through. I drilled and tapped an additional hole to use another set screw on top of the receiver to help lock in barrel. Stock poppet valve. CRC plenum that comes with an 8mm transfer port. Modified pic rail. I would like to turn up the regulator pressure and was wondering how far you can safely go from the stock 1900psi. I want to make sure the gun shoots as good as I am expecting before I decide on increasing the air tank with an extension or bottle. Same goes for the buck rail kit. I just want to make sure this thing is going to shoot before investing anymore into it. I love how the gun looks so far and it has been a fun learning experience. The Notos is a way simpler gun to work on compared to the Gauntlet IMO.
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Unfortunately USPS really did lose my package for an FX .25 barrel. In the meantime while waiting I test fit a scope to see what kind of room I had. Trying to keep the scope as low as possible. I know the buck rail stock sits a bit lower than the stock one and trying to avoid needing an adjustable cheek piece. With 1.1" centerline mounts the scope barely clears the magazine. I modified the sight rail even more to be able to clear a 30mm tube with a 50mm objective lens on the actual scope I plan to use. I have contacted C88 and acquiring the 100mm barrel extension and hardware to run a .22mm 600mm fx barrel instead of the .25. While doing my homework and building this thing I feel like its just not going to have enough to get the good .25 pellets running at a decent speed. See how it goes.
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