Difference Between 301 and 302 Redirects
Many webmasters don't understand the different between a 301 and 302 redirect. You might think that Google and the other search engines would just follow the redirects, but that's where things get complicated. A 301 redirect means that the page has moved to a new location, permanently. A 302 redirect means, that the move is temporary. Search engines need to figure out whether to keep the old page, or replace it with the one found at the new location. Use the wrong type of redirects, and the search engines' view of your web site can get screwed up, badly.
Why does this matter? If you are moving a web page or an entire web site to a new location, for instance if you change your domain name, you want visitors to be able to find your site. A redirect causes the user's browser to automatically forward from the old location to the new one. You might think that Google and the other search engines would just follow the redirects, but that's where things get complicated. When a site moves, that can trigger the Google aging delay. Usually the site drops out of the search rankings for several months, sometimes even a year. We'll come back to this later.
There aren't too many situations where a 302 is appropriate. How often have you temporarily moved a page? It's much more common to move pages permanently. Nevertheless, it seems easier to create 302 redirects than 301s. You can use Javascript or a meta tag to create a 302. Creating a 301 redirect requires special commands in your .htaccess file if you use an Apache server. With Windows servers, creating 301 takes even more time and trouble. That's why there's a tendency for people to mistakenly use 302 instead of 301.
Google recognizes that many people use 302 when they really mean 301. Fortunately, Google isn't bound by any law to take people literally. For the sake of producing the best possible search results, Google can and should look at 302s and figure out if the webmaster really means 302, or if it's run-of-the-mill confusion and they really mean 301.
Whether Google actually handles 302s properly is an open question. If you use a 302 when you should be using a 301, there's a chance Google or some other search engines might keep your old URL in the index, and then filter out your new URL as a duplicate. You might end up with link popularity divided between the two domains, hurting your search rankings. The search engines might figure out how to handle your 302, or they might not. So why take a chance?
When I permanently move a domain, or a web page, I use a 301 redirect. To me, 302s in this situation seem like double dipping. By saying "temporary move" you tell the search engines to keep the old domain or page indexed, but you also want them to index the new one. Maybe you disagree with the Google aging delay, so you use whatever means are necessary to fashion a workaround. You can make that decision, if something bad happens, you accept the consequences.
Are you concerned about losing rankings due to a 301? Simple. Don't change your domain, or don't rely on rankings for your livelihood. In the real world, businesses avoid changing their names because it can appear shady. Who can blame Google for employing the same heuristic: if you're changing domain names, you might be up to no good.
