Spin stability and drag stability

Why don't someone make a air rifle that shoots a traditional full lead bullet. Ik the big bores do this but why not a 22 cal or any of the smaller calibers. It seems that almost all small caliber pcp and springer manufactures make the these guns to shoot the Diablo shaped projectiles. I'm curious as to why they don't put a berral with a high twist ratio on a pcp and shoot full lead projectiles. Is there not enough speed with what we do?
 
Typically, airguns which fire bullets as opposed to pellets are listed by their true projectile size. For example, a .25 caliber pellet for an airgun is .250, while one made to shoot bullets is .257. As far as I know, the .257 is the smallest bullet airgun. While that doesn't directly answer your question, I suspect the bullet advantage for say a .17 caliber is almost nil.

What is more surprising to me, are the really large caliber airguns, like the .457. As I recall, the muzzle energy is over 500 foot-pounds. That's almost insanity in my opinion. 
 
The power is there to shoot bullets. Rarely considered is that part of the apeal of pellet guns is the crappy ballistic coeficient. The low bc means the downrange hazard beyond the intended target is minimal. "Improvements" to the carrying power of airgun projectiles could easily eliminate the virtues over pb guns. 

My favorite gun will shoot 34 grn JSBs or 12 grn wadcutters. I focus carefully when using the 34s, I relax quite a bit more when using the 12s. The 12s will tumble or shatter at the first leaf or twig; the 34s have scary carrythrough.

From an engineering perspective, with maximum stopping power as the design objective, diabolo pellets are non-optimum. If the objective is redefined as effective stopping power applicable in a civilized environment, diabolos start to shine.
 
Personally I hunt/pest with airguns for the benefits of using an airgun. I can pest/hunt in areas that I cant with a firearm because of collateral damage or danger of ricochet or over penetration. Another benefit is the reduced noise unless you want to go thru the paper work and pay the extra cost to suppress a firearm. I find it very hard to beat airguns for small game hunting and especially pesting work. I dont want or have a need for an airgun shooting bullets cause I can just grab one of my powder burners for that if my pellet shooting airgun isnt up to the task. For the people that want/need airguns shooting bullets I say use what you think works best. The airgun bullet scenario just doesnt work for me. Manufacturers may believe the demand isnt high enough or that the benefits are not enough to warrant the production of a bullet ready airgun in a small caliber. Todays pcp can push the heaviest available pellets to some very high fpe numbers with lots of penetration. There are plenty of people who have successfully taken large wild boars with .22 cal pcp rifles. All it takes is good stalking ability and good hunting/shooting skills to get the job done cleanly every time. Thats how it should be even if you are using cast slugs or a firearm to hunt with. Thats my personal opinion on the subject and I know others will see things different.