Five gallon batch in a full keg - drawbacks?

I'm hunting for five gallon kegs, and struggling with the laws of supply and demand. I have found a couple of full size kegs.

If I were to put a small batch one of these, what would be the major malfunction? Would I have to use an exorbitant amount of CO2 to force carbonate?

EDIT: I neglected to make clear that I'm looking for Sanke type kegs

 

I would assume you would have to use a large amount of COS to force carb. Also how are you going to bleed all of the air out of it to leave only CO2 in the head space? That's 10 liquid gallons of head space that you need to fill with CO2.

Might not hurt to prime with some bottleing sugar, might help the CO2 usage (a little)

 

I just bought 2 kegs from Ebay seller beverageelements2009 for a very reasonable price.

Kegs are 5 gallon, clean and sanitized, very good shape -$76 plus $20 shipping. If I had the space I would get more.

 

you will use exactly the same amount of CO2 to force carb. 5 gallons in a 5 gallon container, as you would use to carbonate 5 gallons in a 15 gallon container. you just have more headspace volume to purge.

you will use as much CO2 to dispense the 5 gallons as you would use to dispense a full 15gal keg.

 

You would basically be spending an extra 2 volumes of CO2 to fill the head space of 10g over your volumes used to carbonate, right?

 

Except for the fact that youd need more CO2 to fill up the keg in order for it to actually start pushing and have constant pressure on the liquid...

 

I neglected to mention that I'm looking for Sanke type kegs - the marketplace in San Diego moves quickly ;-)

 

EDIT:


nevermind I misunderstood the question

 

It's okay, it was poorly phrased. I think it comes down to "I'm going to have to waste a bunch of CO2 if I do it this way". So, as in all things beer, it will depend on how badly I want beer at that moment.

 

You could always buy it and then use it in the future as well when u make more beer