@PlotHole  
Ah.
 
Well, once upon a time, it was said the .44-40 cartridge killed more deer, elk, moose, and black bear in North America than all other metallic cartridges combined–though this was before the Winchester 1894 and its .30-30 smokeless powder cartridge replaced it in popularity among North American hunters after the First World War.
 
A 200 grain soft lead bullet with 40gr of FFFg grade blackpowder backing it up may only have a muzzle velocity around 900 feet per second from a revolver–but from a rifle barrel it’ll be more like 1300. It had a reputation for lethality beyond what the kinetic energy figure (mediocre by 20th or 21st Century standards) alone would imply, perhaps because the projectile was already rather large in caliber, and perhaps also because the soft lead usually deformed significantly in soft tissue, flattening out like a rivet to tear a wider hole as it traveled.
 
Depending on how large Equestrian ponies are, .44-40 or its approximate blackpowder era ballistic equivalent (.44 Henry Rimfire, .45 Colt, .38-40 Winchester, etc.) from a rifle length barrel might even be bordering on excessive for them, in terms of lethality.

@Elusive Badgerpony  

 
No, it’s concept art for his Equestria Dreamscape. Baron has done art for Roan, but I understand that tends toward the WWI era. Dreamscape tech is more Civil War and slightly after.
 
@Background Pony #24B0  

 
Yes. See the link for the Spencer rifle below.
 
Here is what the artist had to say:
 
A bit of concept art that I did last year but never got around to posting. This is a pump action carbine that appears in my Equestria dreamscape. It fire pistol caliber, centerfire, blackpowder cartridges and is Equestria’s equivalent of Tacti-Cool. For ponies in that dreamscape this is cutting edge stuff. Since it chambers a cartridge similar to the 44-40 it doesn’t need a very long pump stroke to cycle the action. the closest real world 19th Century equivalent would be Colt Lightning Carbines and Rifles Cartridges are fed from a tubular magazine in the buttstock similar to the Spencer Carbine or Rifle from the US Civil War. It carries 6 rounds in the magazine or an additional round can be in the chamber bringing it to seven.
 
Like the Spencer in our world the carbine can be in theory quickly loaded via thin metallic tube that holds 6 rounds that are dumped in the back end of the stock. Like the similar Spencer tubes these can be rather fragile and finicky at times. Fortunately the designer had the presence of mind to make sure the magazine follower and spring have lanyard so you can’t drop it while reloading in flight. In fact pegasus have been rather fond of the system. Especially amongst some of the Mares-in-Waiting in both Celestia’s and Luna’s courts. Both Squall and Midnight Oil have purchased them with own money, and the Crown has acquired some for testing and limited troop trials.

Hmm. Are those pouches at her waist magazine carriers, then?

Is this updated Roan art?

How would you design a firearm for a four-legged, hooved person?