How can I use 6.5 gallon carboys?

When I first started brewing extract I bought one of these puppies thinking more was better, but I later learned that lots of headspace is bad news bears. I later acquired two more because they were a great deal. Now I've also a 5 gal, and a 6 gal. I am doing my first all-grain brews, two in fact, on friday and saturday, and I am going to use carboys as the primary (any reason why I shouldn't?). Am I okay using these for 5 gallon batches? I used them to dry hop in the past and it turned out okay.. however I'm still new to brewing and I am not sure if that changed it at all. Thanks!

6.5 gallon carboys are perfect to primary 5 gallon batches in.

oh you still will want to consider a blowoff, especially for bigger and wheat beers... they willl fill that extra space up in a heartbeat!

During primary fermentation, your're going to be producing so much Co2, that the headspace isn't a concern. Hell, you could do four gallons or even three in a 6.5 gallno carboy and probably not have an issue.

Headspace may be a concern when using in "secondary fermentation" as the beer isn't likely producing much Co2, so what's in there is all that's protecting agsinst oxidation. Unless you're moving them around a lot, even then it shouldn't be an issue.

At least that's my experience and opinion.

The head space is a big deal if you rack to a secondary fermenter (clearing vessel). This is what the 5 gallon carboys are for. The 6.5 gallon ones are what you want to be fermenting in. Oxygen is GOOD for fermentation.

This is assuming 5-5.5 gallon batches.

That's exactly what I was hoping to hear!! thanks guys!

im not too sure what a blowoff is, although i have heard of it before. ill do some searching when i get home