Just a thought

[Scrog]

Going the opposite way, there is the 22TCM. Not exactly a 9 necked down to a 22 but close. Came out in 2011 I think. 5" barrel @ 2,150fps 4" @ 1,900fps 2,800fps out of a carbine rifle.

[KentuckyBuddha]

The reason you would not want to do that is that the ballistics/performance would be horrible compared to any options that are already available. Like others said there are lots of other options in which you can use rifle pills instead of pistol ones and be better off.

[Ed Songer]

Yah I know that there's better rounds to be had and I'm not saying that I plan on making one! I was just a thought! I thought I'd throw it out there and see what other thought about it!

[2bad4u2]

I think a 9mmBR or 9mm/.308 Win. would be kinda cool.

.35 Remington...

Not exactly. The free bore difference between the cartridges would be significant in addition to the bore diameter. It would be akin to, "throwing a hot dog down a hallway".