One promising pathway to transform forest residuals and slash into a valuable product is through conversion into biochar, which can be used as a soil amendment to increase water retention, decrease nutrient leaching, and also provide co-benefits such as carbon sequestration. Experimental results are presented based on 14 tests of a biochar production machine (Biochar Solutions, Inc.) with seven different feedstocks representative of forest residuals. Averaged across all tests, the machine processed 385 kg of feedstock per hour (wet basis) and produced 43 kg of biochar per hour for an average yield of 11% by mass. The test results show that this machine tolerates a wide range of feedstocks and particle size distributions, but the feedstock should be below 25% moisture content, and 15% ash content or the resulting biochar will have a low fixed carbon content, and operational labor intensity will increase. Based on this series of field experiments, various areas of improvement into the mechanical design of the machine were identified and incorporated into a newly-built biochar production machine with double the throughput capacity.