  High resolution (R$\sim$22,500) spectra for 400 red clump giants, in four
fields within $\rm -4.8^{\circ} \lesssim b \lesssim -3.4^{\circ}$ and $\rm
-10^{\circ} \lesssim l \lesssim +10^{\circ}$, were obtained within the GIRAFFE
Inner Bulge Survey (GIBS) project. To this sample we added another $\sim$ 400
stars in Baade's Window, observed with the identical instrumental
configuration. We constructed the metallicity distributions for the entire
sample, as well as for each field individually, in order to investigate the
presence of gradients or field-to-field variations in the shape of the
distributions. The metallicity distributions in the five fields are consistent
with being drawn from a single parent population, indicating the absence of a
gradient along the major axis of the Galactic bar. The global metallicity
distribution is well fitted by two Gaussians. The metal poor component is
rather broad, with a mean at $\rm <[Fe/H]>=-0.31$ dex and $\sigma=0.31$ dex.
The metal-rich one is narrower, with mean $\rm <[Fe/H]>=+0.26$ and $\sigma=0.2$
dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with
respect to solar in the metal-poor regime, similar to the one observed for
giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend,
but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is
observed at $\rm [Fe/H]=-0.44$ dex. This \textit{knee} is in agreement with our
previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in
metallicity than the one reported for the Bulge micro lensed dwarf and
sub-giant stars. We found no variation in $\alpha$-element abundance
distributions between different fields.
