The interaction of electron–electron scattering with the size‐effect, with electron–phonon scattering, and with electron‐impurity scattering is measured and interpreted on high‐purity and W‐doped single crystalline molybdenum in the temperature range T = 1.6…30 K. On a set of more than 30 single crystals with different axis orientations the range down to 1 at · ppm impurities was realized, resulting in residual resistance ratios up to RRRimp = 1 × 106 and in electron mean free paths up to λimp = 12 mm. The interference of normal electron–electron scattering (NEES) with the size‐effect (Gurzhi effect, Knudsen effect) is proved in crystals with RRRimp ≥ 100 000. Relaxation times for NEES and electron‐umklapp scattering are estimated. Different types of magnetoresistance (MR) are measured in longitudinal and transverse magnetic fields . An orientation‐independent ωCτ value for Mo is deduced. The size‐effect reduction in longitudinal field is shown to be consistent with the Chambers calculations under consideration of NEES. The high‐field transverse magnetoresistance (TMR) of the high‐purity crystals is dominated by the static skin effect: the surface TMR short circuits the compensation‐induced bulk TMR which is shown to follow over 10 orders of magnitude without any sign of saturation.