Direct imaging in exoplanetary astronomy proves to be one of the best methods for definitively characterizing exoplanet properties and chemistry. The HR 8799 system is one of the best known testbeds for studying through direct imaging techniques, with four exoplanets seen with greater than 5-sigma detection in J- through L-band. However, in previous studies, longer wavelength M-band observations have not resulted in conclusive detection of the innermost planet, HR 8799e. Exploring longer wavelengths is crucial to probe the abundances and chemistry of exoplanet atmospheres. More specifically, M-band observations access the strongly-absorbing and well-understood CO ro-vibronic mode at ~4.6 microns. From CO absorption characteristics in the HR 8799 system we may explore atmospheric properties investigating non-equilibrium chemistry, the C/O ratio, cloud properties, and metallicity. We present high-contrast NIRC2 Keck data processed with an advanced background removal technique based on LOCI background subtraction. We directly optimize the signal-to-noise of the planet signal using the Julia-based Signal to Noise Analysis Pipeline, augmented with a forward model matched filter. We present detection limits based on current analysis and show this combination of techniques serves as a powerful probe for high contrast imaging even in typically background-limited M-band data.