@Zero_HP: I just imported the Bren at my end and all fine. For the Pickups, you cannot multi select files. The first prompt is for the weapon pickup FPE only e.g. Bren.FPE. Next prompt after selecting the weapon is for the ammo e.g. Bren_ammo.FPE. Again, at the moment you can only select one file. Also, make sure you have the FPE's in the correct folders. For your pickups, you have them all under entitybank. On mine it's entitybank/ww2 weapons pack. Make sure the main gamecore folders are set up correctly. For the "ww2 weapons pack", you need a folder in FPSC as follows->gamecore\guns\ww2wp. This will be mirrored in GameGuru. If you have made your own folders, that's great, but just make sure they correct and in the correct subfolders etc. But it might be better to install FPSC and models packs using the original file paths as the program is not flexible for customised paths (at least not yet).
Iron sights should work ok in GameGuru, you won't see them in the app screen, that is just for show. Do you see them in GameGuru? The program (if I recall as it's been ages since working on it last) should use a GameGuru default one but you can experiment with the FPSC ones. For the Bren and generally all the ww2wp guns, there are 2 folders under gamecore\guns\ww2wp\bren named "dynamic crosshair" and "static crosshair". you may find most of the old FPSC texture files are not compatible though or need a paint program to modify.
For the hands not coming out, my video "Weapon Welder 1.6 Hands texture issue solution" explains what to do. This gist is that you load the HUD.X file (backup first) into a model program such as Fragmotion and re-export out but "uncheck" the "export groups" box or something similar. The textures should then come out correctly. Remove any old HUD.DBO files first before opening GameGuru though.
Most of the guns have been tested so they should come out correctly in GG. You may need to make some personal preference modifications. But if there are any odd fixes that need to be applied to the program, I will look into it. The program tries to correct any path issues with textures, but there is always a scenario not covered at some point but generally most have been addressed.
Another tip, FPSC textures come out quite bright, I recommend using a paint program to tone them down and save back out. Should be on a video above
Maybe the next release will include multi file selection and better GUI.
Hope this helps.
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FPSC to GameGuru Tools: AutoWelder/SegAutoWelder, Entity+Weapon Welder, FPEtoBAT