Other models of horse pistols had a long metal tab almost the whole lenth of the gun's left side opposite that of the flint, pan etc. You could use that long metal clip to hang the gun on a horse or about a horse any place convient to you.
It's was about as big as you can pack and still shoot from a horse without putting down one hand. They are also big enough to dispatch a horse that went lame and only recourse is to put it down.
And finally but not last, the pistol has a metal butt peice that is very large and stout. You could knock a bad guy highwayman down and keep going. They had alot of heft to them, pounds of heft.
In those days they had horse units known as artillery, supply or even a bit of heavy horse or dragoon. But the calvary as we understand it in the late 1800's were only swords and pistols suited to horseback combat against infantry on foot in the colonial times. LAter calvary had pistols tied to a string to keep them aboard horse and a long rifle to fight beyond pistol range.
The English were pretty good, Indians even better and the french not so bad. And to defeat a horse unit you move into ground not so good for horses.
Finally but not last, landed gentry riding in coaches had very short shotgunlike coach guns and those were the tatically dangerous weapons in thier day for close up and personal defense.
If you have been inside a stage coach, there isnt much room for 6 people in a space not much larger than a Mc Donalds mealtable.
Might be where you ended up if you got hit by one! Ok, sorry I don't have anything but that lame joke to contribute... 
