How risky would be a visa run to S. Korea?

Hello everyone. I'm planning to go to Japan next month and I want to stay 180 days it's mean six full months. I'm uruguayan then I'd be getting 90 free days tourist visa when I go through customs so my plan is when my first 90 days are over then I'd be flying out to S. Korea, to stay there a week and then come back to get another 90 days free visa tourist so I can stay 180 days as I plan but my doubt is since I'm uruguayan will immigration officer let me enter back to Japan after my run? since Uruguay isn't a country of first world I dunno if it's going to work, I need to know how riscky it can be! I have enough funds to stay six months and I'll make an itinerary just in case. I won't be working or anything like that, I only want to enjoy Japan over six months.

Thank you.

It's impossible to say "how risky" it is, as that would require detailed statistics about success rates, which we do not have.

Uruguay seems to only have a 90 day visa waiver agreement. Quite honestly, I think you wouldn't be allowed back inside the same calendar year.

Sorry - unclear.
By which, it doesn't have a 6-month agreement (note 8), like the UK.
http://www.mofa.go.jp/j_info/visit/visa/short/novisa.html

How does visa waiver work then? I meam I have heard stories of people that are from USA and Spain and they were successful at getting their visa runs by going to S.Korea and coming back to Japan and USA and Spain tourists also have 90 free days like Uruguay so what's the difference? I don't get that part.

I have no idea how visas work for your country, but if you have the funds and the itinerary is there not a way to get a 180 day visa in advance of your trip?

I called the embassy in my country and they said i could go for 90 days that's why I wanted to do a visa run to S. Korea but seems visa run are valid only for waiver countries? I didn't know if that's the issue.

If there is an agreement for more than 90 days, then I think it is no problem.

If people from those countries have tried it and been successful (even if they haven't), you are welcome to try. However, I would strongly, strongly, strongly suggest that you have a back-up plan. Immigration have an absolute right to refuse entry.

The traditional understanding is that you can usually get away with what you are suggesting. One "visa run" per year is thought to be normally allowed.