No it's interesting.
I'm afraid the rosy view of the Mccellan saddle is not shared by all. If it works for someone it works, if they like that's enough for me. But history is more complicated.
I do not find any indication that the Mcclellan even came in different tree widths. The army was like that - one size fits all, so I can believe it was possible. The saddles were produced in large numbers and bought en masse, so I doubt there was a lot of individual fitting!
I rode in a Mclellan saddle when I was young as there were a great many of them around from war surplus and even cropped up at rental stables. It was not too bad for the occasional ride, as long as the type of horse was suited. I felt it went better on a horse that was more stocky and had a broader back.
The type of horse we have today is a lighter and narrower animal than 100 or 150 years ago when the Mcclellan saddle was developed and used. That changes the shape of the back. That said, if you look at books from 1850 there is hardly a single breed of horse named that we would recognize the name of today or know anything about. And...a little longer ago than that the shape of back liked was the 'double back' that was shaped like an apple with a dimple in it, it has gradually changed since then.
I will say that while our poster finds Mclellan saddles comfortable a whole lot of people did NOT and there are quite a few diaries and writings cursing out the discomfort of those saddles to man and beast, if you nose around. I can remember reading these as a young person and having quite a laugh, but as a skinny kid I would have been comfortable sitting on any saddle or no saddle. The saddle was developed around 1860, I think, and saw use in the Civil war though many riders reported for duty with their own English or Plantation saddles.
Look at some old cavalry photos of horses sometime, and check out the saddle sores in various stages of healing and not healing and white healed scars. Those old Mcclellan saddles went on the horses whether they fit them or not, and if the choice was between killing or soring a horse and mission accomplished, it was mission accomplished. Those horses got used hard. It wasn't just the Mcclellan saddle that made the 'Remount' business a thriving and active one, it was just the use the horses were put to as well.
Of course the Cavalry was not always using Mcclellan saddles either. If you look at most of the films they are not in Mclellan saddles at all after a certain point in time I think they were not generally used.
In the US horse cavalry was disbanded in 1964 though we have one remaining ceremonial cavalry unit at Fort Bliss. And they look for all the world like they do their ceremonial rides in Mcclellan saddles, but I am not 100% sure about that they are the same pattern as back in the civil war, by the early 1900's the rigging had already been changed several times, and the ones I rode in looked very reduced compared to those I saw in the cavalry museum displays.
Many times later on, the word 'cavalry' was used not to describe horse cavalry but fast strike units that did not have a single horse. Many European nations were disbanding their cavalries in the early 1930's and even so there was a lot of horse action in Europe.
I don't think we used more than a few thousand horses in WW II, and most of that in Burma and the Phillipines (and a lot of that pack and harness), but the Europeans sure did, over the course of WWII the Germans used close to 3 million horses and the Russians used more(the cavalry units were not 3 million in size, many of those millions were replacement, replacement and replace again and again), but they did not use Mcclellan saddles either.
The last cavalry charge of the US was at Bataan in WW2(and the horses in it had to be eaten as the army got pinned down and ran out of food), and the last horse action of any kind by any US army unit was in Austria in 1945.
The only other countries where the McClellan saddle ever got adopted were Rhodesia and one other country I believe.
Too, saddle fitting today is far different. In the past much more of the weight went on the top of the back and now it is quite scientific and some of the weight of the rider is born down the sides of the front of the saddle because of very careful fitting of the width of the tree. Panels are available in a number of shapes that conform more to the shape of the back, a custom saddle fitted to the individual horse can consist of numerous measurements and even a trace, cast or form made of the back. Saddles are also now often restuffed every few years either to provide a more comfortable seat to horse and rider or as the horse develops more muscle or less and his shape changes.
Added in is the fact that very few people go for long rides these days and really put a lot of pressure on their horses - most rides are brief, around the field and on flat ground, and riders also generally do not ride every day. It's for the majority an on again off again thing.
The distance riders we have today either do a very good job at fitting their tack or they don't. I've seen some distance horse's backs in very good shape and some ... not so good. But you very, vcry rarely will spot a distance rider using a Mcclellan saddle. Yhey use English or various specialty saddles, Western or modified Western design intended for Endurance.
Some website info:
"In the 20th Century, a serious effort was made to replace the McClellan through tests of the US Army's M1912 equipments. The M1912 saddle proved to be unsuccessful in the Punitive Expedition, but it demonstrated a great departure from the McClellan design, resembling in some ways the British Universal Pattern saddle. Subsequently, the Army tested the M1917 saddle, which was not adopted.
Enormous quantities of M1904 McClellans were purchased by the US Army in WWI, effectively preventing any new saddle from being adopted for general use for decades. The US Army did approve a saddle of the English saddle type prior to WWI for officers, and after the war approved another, with the adoption of the Philip's saddle for officers.
"
Here, read and learn! 
