I recently sold my Brno ZKK 6.5-06. It was a beautiful rifle but I had no real use for that calibre. It had been rebarreled for the 6.5 cartridge but had the original barrel sling hanger and front sight on the new Douglas barrel. Also had the pop up peep sight and the single set trigger.

You need to be careful if attempting to lighten the trigger pull, adjusted from the top using the screw in front of the rear tang screw (visible in one of the photos). If adjusted too light the bolt will uncock as it is closed especially if worked rapidly when reloading.

Adjust the set trigger until the bolt does uncock when closing rapidly then gradually increase trigger pull weight until the bolt does not uncock when rapidly closed. I did not touch the trigger on my rifle when I took possession of it but noticed the bolt uncocking when on the range even without working it vigorously.
A live cartridge did not fire as it uncocked but potentially a cartridge could fire if the bolt was slammed close after feeding a round from the magazine and chambering it. BE CAREFUL.

There is info published on some forums on the trigger mechanism and adjustment, I have it if you need it.