Howdy...
Since I no loger resides in the great state of Texas, or in the US at all in fact. I need to exploit the facinating gunlaws of my home country as much as possible. (they're not too bad and they have some funny loopholes ;)) Basically I need a "reason" to get a permit for a gun, and since i just became a member of the local IHMSA club I can get a permit for a riflecaliber handgun... And what would be more natural that an AR15 pistol to topple those 300 yard steel rams? (ok, if i actually want to win, I'll just pop a pistol barrel and handgrip on my conteder...)

Now, due too the sad fact that our government adopted a AWB inspired regulation a year before you got rid of it... ht
So can a RRA (or similar good 9mm pistol upper) be used with the carbon lower? I guess i would need to chage the buffer tube for 9mm too, and i would prefer to use colt 9mm mags so i would need an adapter to fit in the carbon lower too.
Is it doable? and what considerations do i need to take? And so forth and so on.

Maybe I'm reading this wrong, not familiar with where your at, but why not get one of these?

9mm Bushy Carbon Pistol.

It's to heavy.... And the evil handprotecting bit around the barrel would make it a big no no.
Alsoactually would like to shoot .223 also.

Okay, Well it is doable.  But I'm not sure I understand the weight thing and not sure where you are and what laws apply.  So negating all that.

I have a Bushy Carbon 15 Pistol and I have an RRA M4 profile LAR-15.  Yes The RRA Upper will fit on the Bushmaster Lower.  

Things that I would think you would want to consider are the buffer tube system on the Bushy Carbon Pistols involves a shortened Bolt Carrier Group with the weight in the buffer tube actually extending inside of the upper receiver and into the back of the Carrier.  So you have to unscrew the buffer tube and pull the spring and weight off before you can push the back pin and pivot the upper receiver off.  

The RRA upper will come with a standard Bolt Carrier Group.  So you will either need to use the Bushy Buffer tube system and bolt carrier with it or get a new Carbine length tube and Buffer System.

Hope that helps!

The weight thing is one of the criteria wich defines what is a good gun vs a bad gun.
We all know that pistols over a certain wight, particulary if you can hold them two handed (without using both hands on the grip) and they have the magazine in front of the trigger are particulary evil, and known for making unsuspecting owners rob banks, join criminal gangs ans mass murder other people...

so fortunately the carbon 97 pistol is defined aas a "good gun", and then using the carbon lower for a rra 9mm upper for training purposses is perfectly safe and legal...

Since colapsing stocks are known to make people do the same hienous things, i got a spare one from my Bushmaster VM 20" including the buffertube, springs and whatnots. SO i do have a regular carbine buffer set up to use with 9mm upper. the main question, wich i think have been answered is that with changing the buffer, a rra pistol upper would work and fit to a Bush carbon lower.

How about magazine blocks, like the Hahn block or the RRA magblock, would those fit?

 

Sorry, I don't know the answer to that.  You might want to start a new thread for this question.