Spectrum shape measurements in nuclear $\beta$ decay are a versatile observable. They can be used to test physics beyond the Standard Model with results being complementary to high energy collider experiments. In addition, the $\beta$ spectrum shape is a useful tool to probe Standard Model effects. One of those effects is called Weak Magnetism and is induced by QCD interactions between quarks in the nucleon.

In order to study effects on the order of $10^{-3}-10^{-2}$ in the $\beta$ spectrum shape, a new prototype spectrometer, named miniBETA, was designed and built. It consists of a 3D low-pressure gas tracker, i.e. a multi-wire drift chamber with hexagonal cells, and a plastic scintillator for triggering the data acquisition and recording the $\beta$ particle energy.

Results of the miniBETA spectrometer characterization, supported by Monte Carlo simulations in Geant4 and Garfield++, are reported here. In addition, the preliminary results from $\beta$ spectrum shape measurements on the allowed Gamow-Teller transition $^{114}\text{In} \rightarrow ^{114}\text{Sn}$ are presented, including an extraction of the Weak Magnetism form factor.