Sauer SSG 3000 muzzle thread ?

Yes, the "American" SSG3000 rifles were 5/8X24 those were in the cheaper composite (I don't mean that derogatory, just comparing it to the McMillan). So maybe I should clarify all the McMillian rifles, and other European variants were 18X1.0 (I had a Sauer STR in a laminated stock which is the same barreled action as the SSG, and they also had a chassis for a short time but I don't think it ever made it into the US).

Sorry for the confusion, but the difference between 5/8" and M18 should be very apparent (you can tell with a tape measure, no need for a micrometer).
 
I really like the SSG, especially with the barrel change system & slightly longer action where you can easily run a 6.5X55. The trigger, safety, and action is excellent (trigger is almost as good as the TRG). But with that being said the TRG is a very close second to Accuracy International as far as my all time favorite. For reference I have owned 1 SSG3000, the STR200, a TRG with 3 different barrels, 2 AWs, & now an AT.

TRG is my pick of the 3. Only down side is having to send it off for a new barrel. Where you can order drop in barrels for the SSG from Benchmark.
 
Thanks for your advice , the thing is the only available calibers where I’m right now is only military factory calibers like 308, 338, 5.56

I shot a steyr ssg69 k2 last week and it was as accurate as the trg
 
The SSG 69 is a cool rifle. I had a PII years ago and it was such a nice rifle. I always wanted to build off the action, but never did. It does have its limitations though, mainly the bottom metal (plastic), magazine, and stock all like to crack a little too easy...