A chromatic brass instrument (i.e., one equipped with toneholes, a slide or valves) is in effect an assembly of tubes with different sounding lengths and different bore profiles. Although the differing bore profiles will result in differing timbral characteristics, these differences in a well designed instrument cannot be too great if the instrument is to have a consistent sound quality in scalar passages. This paper presents investigations into the timbral effects of non-linear propagation in chromatic brass instruments with varied sounding lengths. Experimental results are correlated with calculated values of the Brassiness Potential parameter. Additionally, results are presented which compare the brassiness curves of instruments with similar Brassiness Potential but differing in their absolute bore diameters. An explanation is offered for the perceived phenomenon that narrow-bore instruments are brighter than wide-bore models of the same kind of instrument.