This week I've been testing the Newport vs. Jeddo. Both are called buck, but both have a lot of undersized pieces. The testing consists of "normal" offseason DHW runs of 7-30 minutes plus a few longer runs to make some steam. Stoker set on 8 teeth = 40 lb/hr of feed; air varied based on fire appearance in steam runs to try to approximate EFM fire pattern.
The Jeddo went first. In a little under 4 hours of cumulative run time spread over 3 days, 154.9 lb were burned and 20.1 lb of ash and unburned coal were produced, for a total of 13.0% ash and unburned. I believe Jeddo normally runs 8-9% ash in lab tests, so 4-5% of the coal went unburned. To those who aspire to 0 percent unburned this may seem like a lot, but the OE manuals I've seen say the normal amount of unburned should be around 10-15%, and that an excessively low unburned coal percentage is a sign of too much air. In fact, the ash ring during the test was bigger than ideal, indicating too much air. If the test were repeated I'd expect the unburned percentage might be higher.
Then came the Newport. Early on I got the impression that this coal needs long runs to fully catch, so I stretched out the runs (most between 14-37 minutes). It also seems to be less dense than the Jeddo. In a little less cumulative run time than the Jeddo, 133.9 lb were burned and 30.2 lb of ash and unburned coal were produced, for a total of 22.6% ash and unburned. The visible amount of unburned coal was higher than it was with the Jeddo, the fire looked different and the ash removal system worked harder. The coal did hold the fire for over 10 hours without the stoker running, and gave overall performance closer to reasonable than I was expecting.