We measure the Sunyaev–Zel'dovich (SZ) signal toward a set of 47 clusters with a median mass of 9.5 × 10^(14) M_☉ and a median redshift of 0.40 using data from Planck and the ground-based Bolocam receiver. When Planck XMM-like masses are used to set the scale radius θ_s, we find consistency between the integrated SZ signal, Y_(5R500), derived from Bolocam and Planck based on generalized Navarro, Frenk, and White model fits using A10 shape parameters, with an average ratio of 1.069 ± 0.030 (allowing for the ≃ 5% Bolocam flux calibration uncertainty). We also perform a joint fit to the Bolocam and Planck data using a modified A10 model with the outer logarithmic slope β allowed to vary, finding β = 6.13 ± 0.16 ± 0.76 (measurement error followed by intrinsic scatter). In addition, we find that the value of β scales with mass and redshift according to β ∝ M^(0.077 ± 0.026) x (1 + z))^(-0.06 ± 0.09). This mass scaling is in good agreement with recent simulations. We do not observe the strong trend of β with redshift seen in simulations, though we conclude that this is most likely due to our sample selection. Finally, we use Bolocam measurements of Y 500 to test the accuracy of the Planck completeness estimate. We find consistency, with the actual number of Planck detections falling approximately 1σ below the expectation from Bolocam. We translate this small difference into a constraint on the effective mass bias for the Planck cluster cosmology results, with (1 - b)=0.93 ± 0.06