Predictable tuning behavior and stable laser operation are both crucial for laser spectroscopy measurements. We report a sampled grating quantum cascade laser (QCL) with high spectral tuning stability over the entire tuning range. We have determined the minimum loss margin required to suppress undesired lasing modes in order to ensure predictable tuning behavior. We have quantified power fluctuations and drift of our devices by measuring the Allan deviation. To demonstrate the feasibility of sampled grating QCLs for high-precision molecular spectroscopy, we have built a simple transmission spectroscopy setup. Our results prove that sampled grating QCLs are suitable light sources for highly sensitive spectroscopy measurements.