The uniformity of a feed mixture is determined from the coefficient of variation (CV) of 10 samples in a single batch of feed. The feed industry standard is a CV of <10% using a single source tracer such as salt, trace minerals, or iron filings. The uniformity of mix can be affected by many factors, including mixer design, particle size of the ingredients, and mixing time. Previous research has determined the minimum mix time to maximize the mixing efficiency, but some hypothesize that over-mixing may lead to ingredient segregation. However, there is limited data regarding the effects of extended mixing or of the analytical marker appropriate for maximum precision of the assay. The objectives of this experiment were to determine (1) the effects of extended mix time, and (2) particle size of the marker on the CV in a corn-soy swine diet. Treatments were arranged in a 3 × 7 factorial design with 3 salt particle sizes: fine (350 µm), medium (464 µm), and coarse (728 µm) and 7 mix times: 2, 3, 5, 15, 30, 45 and 60 min. There were 3 replicates per treatment and 10 samples per replicate. Salt concentrations were determined using a Quantab Chloride Titrator. Data were analyzed using the GLIMMIX procedure of SAS. There was no interaction between mix time and salt particle size (P > 0.60). The extended mix time did not result in segregation (P > 0.30; 9.6, 11.5, 11.8, 11.2, 12.50, 10.6, and 10.1% CV for 2, 3, 5, 15, 30, 45, and 60 min, respectively). Particle size of the salt significantly affected the uniformity of mix (P < 0.01; 20.7, 8.4, and 7.7% CV for the coarse, medium, and fine salt, respectively). These results indicate that feed did not segregate after mixing for one hour and that greater number of particles per gram increased the precision of the analysis, likely due to an increased probability that the tracer was present in proportionate quantities in the sample tested. More research is needed to determine if sample size or number of samples per batch should be increased, as well as the effect of diet particle size on uniformity of mix.