In this work we study the shape of the projected surface mass density distribution of galaxy clusters using weak-lensing stacking techniques .
In particular , we constrain the average aligned component of the projected ellipticity , \epsilon , for a sample of redMaPPer clusters ( 0.1 \leq z < 0.4 ) .
We consider six different proxies for the cluster orientation and measure \epsilon for three ranges of projected distances from the cluster centres .
The mass distribution in the inner region ( up to 700 kpc ) is better traced by the cluster galaxies with a higher membership probability , while the outer region ( from 700 kpc up to 5 Mpc ) is better traced by the inclusion of less probable galaxy cluster members .
The fitted ellipticity in the inner region is \epsilon = 0.21 \pm 0.04 , in agreement with previous estimates .
We also study the relation between \epsilon and the cluster mean redshift and richness .
By splitting the sample in two redshift ranges according to the median redshift , we obtain larger \epsilon values for clusters at higher redshifts , consistent with the expectation from simulations .
In addition , we obtain higher ellipticity values in the outer region of clusters at low redshifts .
We discuss several systematic effects that might affect the measured lensing ellipticities and their relation to the derived ellipticity of the mass distribution .