STEP 1 You must have txd workshop downloaded( I am 100% sure everyone already has it but anyways you can download it from this link)TXD workshop
STEP 2Open txd workshop and click open IMG instead of Open txd , and open gta3.img
after you've opend Gta3.img it should look like this
STEP 4Search sniper.txd on the search bar.
STEP 5 Now click on "SNIPERcrosshair", then click insert and insert the desired sniper scope
click save and you're done
Now you can combine the best sniper texture with the best scope