Designed by Rocky Gibbs in the mid-1950's. Gibbs designed several cartridges ranging from .24 caliber to .30 caliber, all based on the 30-06 case. Gibbs' cartridges feature a shoulder moved far forward than it's parent, increasing case capacity appreciably.
The shoulder on the 270 Gibbs is almost a tenth of an inch further up the case than the standard 270 Winchester. Accordingly, fireforming new cases is not as simple as the Ackley technique. The most successful method of forming Gibbs cases seems to be: to eck-reduce .30-06 cases until the bolt can just be closed on them (creating a false shoulder) and then fireform them using maximum .270 Winchester loads.
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This is a quote from ammoguide.com about the 270Gibbs