I have recently aquired a rifle with the stamping on the barrel identifying it as a 256 Gibbs. I was told that this cartridge is identical to the 6.5X55 Swedish Mauser. Is this so?

Not sure about the 256 Gibbs specificly, but the "standard" Gibbs package is a 30-06 case (7.62x63) with the shoulders blown out and the neck shortened to 1/4". The 25-06 (still to short in the shoulder however) would probably be closer to it than the 6.5x55. Power wise it would be in the 257 Weatherby class.
To make such a brass (if you buy the rifle), run 30-06 brass into a 256 Gibbs die until you can just close the bolt on the "false shoulder" created by the die. Fireform with a light charge of pistol powder (IE: Bullseye) topped off with "grits" (corn meal) all packed in with TP in the neck.

Of course I'm thinking of the line of cartridges made by the American wildcatter Randy Gibbs, and don't know if there's another Gibbs out there (in which case, ignore every thing I just said).

Appears that it is. One has to be sure whether it's the English maker Gibbs or the American wildcatter Gibbs.
http://www.fireflyarms.com/cartinfo/caseinfo.asp?id=119

Bye
Jack

Tailgunner types faster than I do, and my comment about the two Gibbs was not directed at his post. Further checking shows a slight difference in shoulder diameter, but that could be an error in measurement as the specs on these older cartridges aren't set in stone. The English Gibbs also developed that little .505 elephant plinker.

Bye
Jack

The English 256 Gibbs cartridge - developed in 1913 for Gibbs proprietory bolt action magazine rifles - was loaded with either 135 grain or 145 grain projectile .

Note that the cartridge is definetly not the same as the 6.5 x 55 Mauser round - the case length is 2.176" as against 2.156" for the Swede , the shoulder of the Gibbs is further forward 1.792" against 1.722" for the Swede , the shoulder diameter for the Gibbs is 0.418" against 0.433" for the Swede .

Having said all of that , if you are brave I imagine you could fire form 6.5 x 55 cases to suit , but not on my recommendation thanks . Sounds like a nice gun you have , congratulations .

I am indeed referring to the English Gibbs. It does sound like a nice rifle, unfortunatly, it's a nice barrel that been screwed on to a VZ-24 action.
Thanks for all the information guys.