Might be worth looking at how the RHS guys managed to work their reload script so that you can reload 1,2,3 etc. shells instead of the whole 6 when you've fired one.
Hey THERUSSIA, please put your suggestion on the feedback tracker https://community.sogpf.com/threads/44-Bug-reporting
Keep in mind that scripted solutions that are acceptable in mods might not pass Bohemia Interactive Quality Checks.