If it was a gallon short it would be a bit over carbed. But not bottle bomb or anything too drastic. But if you have a scale (which you should) then if it's a 5 oz packet then it would be 1 oz/gallon of beer, and you could just hold back that amount at bottling time.
Like my snazzy new avatar? Get Sons of Zymurgy swag, here, and brew with the best.
Revvy's one of the cool reverends. He has a Harley and a t-shirt that says on the back "If you can read this, the bitch was Raptured. - Madman
I gotta tell ya, just between us girls, that Revvy is HOT. Very tall, gorgeous grey hair and a terrific smile. He's very good looking in person, with a charismatic personality... he drives like a ****ing maniac! - YooperBrew