Hi all..does anyone know a proper bootloader as the title says ? I want to change the actual crystal (16 Mhz) to an error free baud generator crystal to get reliable rs485 comms..Thank you..
You can recompile Arduino bootloader, just change the frequency from Makefile.
In the past, I have used the older (not optiboot) bootloader from Arduino/hardware/arduino/bootloaders/atmega; you can find compiled .hex file (for 14.7456 MHz) from http://files.tkoskine.me/arduino/14mhz_bootloader/ (Note: it has been few years since I last time used that bootloader, it might or might not work on your Arduino/atmega328p).