Questions about building from kit

Hello all

Purchased a HK G3/91 parts kit from Atlantic firearms as well as the barrel. I purchased a complete receiver from gun broker as well and do not believe I need any more parts.

So far I'm unable to screw on the included compensator onto the newly made barrel, the threading seems different? The barrel runs 5/8x24 but unsure the threading on the comp

I have yet to start constructing it fully, but I'd rather ask before hand if there's any tips or need to knows about building this into a complete firearm, any help is appreciated thanks!