This was no ordinary test – it appears they expected this to be a significant contender. Judging from the near silence following the few early letters of review returned from officers the Campbell was not a success. From the letters sent by reviewing officers, they appeared to like the saddle and shape, but the durability was poor, easily breaking and occasionally injuring horses. No surprise considering the nature of the patent spring steel and sidebar pivot fittings that were expected to take the abuse of mounted service on the frontier.
This emphasis on the desired shape of the new saddle is significant – after many years, the ‘hussar-lust’ appears to have waned. Long-heard criticisms of overly tall pommels and cantles and the gyrations they forced upon diminutive dragoons and cavalrymen were being addressed. Styles of civilian saddlery of the time appear to have had some effect as well, as the ‘spoon’ of the old hussar cantle was replaced by the very common smooth low oval seen in so many other contemporary designs. A number of Grimsley-type officers saddles have been reported that show an oval cantle, as a private purchase option — the author recalls seeing one sold by Norm Flayderman in the mid 1980s. To have this specific change demanded by the cavalry board in 1855 has great importance, as we see this design feature appearing again in the very near future.
Campbell’s equipment set contained four distinct patents, the tree patented July 1855, and the remaining three patents dating December 1855 concerned with the arrangements of the holsters, valise pouches and methods of attachment. Reading Campbell’s tree patent of 10 July 1855, we find an interesting idea where the two sidebars are connected with flexible spring steel arches, firmly attached to sidebars at front and rear. The cantle and pommel are primarily attached via a fitting/flange at the tops of these arches, and a pivot/hinge point at the middle base of the pommel/cantle arms where they connected with the sidebar. This would which would allow the sidebars to flex under load, pivoting to adjust to the changing conformation of the horse during long marches and campaigns.
The noted ‘default position’ of the sidebars is for the spring arches to keep them as ‘flat’ as possible, so that as the animal lost muscle mass, the whole sidebar would swivel to a more vertical position. Necessarily, the main stress in this state would be the flex points of the spring arch as it naturally constricted through the interior arch, and the top edge of the sidebar which would be the main area of pressure as the springs were under tension. This also required substantial wooden cantle and pommel pieces, as these were necessary to limit the range of motion for the spring-loaded sidebars. The system as a whole would actually increase the tension of the spring arches and stress on various points of the tree as a campaign or march proceeded, and horses lost weight and condition. 
Above are noted artist Randy Steffen’s depictions of the Campbell trial saddle, which are based on the detailed patent drawings and descriptions. They are actually quite well done, and are useful here for general identification purposes.
The original design, as shown in the patent drawings was attempting to maintain the long-used hussar type form. The cavalry board of 1855 made important design element changes, that reflect the changing style preferences of the time.
Images courtesy The University of Oklahoma Press1855 Ordnance General Order No. 13 Regarding New Horse Equipments