301 re-direct to a duplicate site question

[mark90196]

Hi
I wish to change the domain name and template on an ecommerce site that gets around 50k visits per month.

So I have created the new site under a new domain name and apart from it being under a new template it is a duplicate of the original site. I am nearly ready to activate a 301 redirect from the old site to the new site.

However some of the new site has already been indexed by Google so I am wondering what will happen to the already indexed urls of the new site in google search rankings when I inititate the 301.

Obviously at the moment the urls of the old site are indexing much higher in google search rankings than the url's of the new site so when I 301 the old site urls to the new site how will google handle the changes?

Will there be 2 versions of the same url in search rankings or will the url with the best search rank keep its position and the existing position dop off, or vice versa?

I read somewhere that I should have blocked crawler access whilst creating the new site but it does not explain why so this has me concerned somewhat.

Any advice is appreciated.
Many thanks

[dipper]

In the time it takes between when you push the new domain live, and Google recrawls the old URL - thereby following the 301, there is a chance the new page could be indexed and both would appear in the SERP's. That will be resolved once Google has revisited the old URL (one by one) and followed the 301 to the new page on the new domain. Once that is done, for each URL then there should be no issues. After a few weeks there should be no old URL's in the SERP's.

Use,
site:oldurl.com
site:newurl.com

Should see the old one declining over the weeks after launch of the new site, and the old url 301's.

Good luck!

[edited by: Robert_Charlton at 4:13 am (utc) on Jan 13, 2016]
[edit reason] removed smilies after colon in site: operator [/edit]