  We describe Sunyaev-Zel'dovich (SZ) effect measurements and analysis of the
intracluster medium (ICM) pressure profiles of a set of 45 massive galaxy
clusters imaged using Bolocam at the Caltech Submillimeter Observatory. We have
used masses determined from Chandra X-ray observations to scale each cluster's
profile by the overdensity radius R500 and the mass-and-redshift-dependent
normalization factor P500. We deproject the average pressure profile of our
sample into 13 logarithmically spaced radial bins between 0.07R500 and 3.5R500.
We find that a generalized Navarro, Frenk, and White (gNFW) profile describes
our data with sufficient goodness-of-fit and best-fit parameters (C500, alpha,
beta, gamma, P0 = 1.18, 0.86, 3.67, 0.67, 4.29). We also use the X-ray data to
define cool-core and disturbed subsamples of clusters, and we constrain the
average pressure profiles of each of these subsamples. We find that given the
precision of our data the average pressure profiles of disturbed and cool-core
clusters are consistent with one another at R>~0.15R500, with cool-core systems
showing indications of higher pressure at R<~0.15R500. In addition, for the
first time, we place simultaneous constraints on the mass scaling of cluster
pressure profiles, their ensemble mean profile, and their radius-dependent
intrinsic scatter between 0.1R500 and 2.0R500. The scatter among profiles is
minimized at radii between ~0.2R500 and ~0.5R500, with a value of ~20%. The
best-fit mass scaling has a power-law slope of 0.49, which is shallower than
the nominal prediction of 2/3 from self-similar hydrostatic equilibrium models.
These results for the intrinsic scatter and mass scaling are largely consistent
with previous analyses, most of which have relied heavily on X-ray derived
pressures of clusters at significantly lower masses and redshifts compared to
our sample.
