Assumption 1:
A 9mm generates less recoil than a .45 round

Assumption 2:
A burst from a 9mm SMG should be more controllable than a burst of .45 rounds

Does that make sense? Agree or disagree?

-Siege

Make .45ACP SMGs heavier than 9mmP SMGs, and consider that to take care of the matter. Or allow more 9mmP SMGs to have RC than .45ACP SMGs.

I do both.

There really isn't any way to handle slight changes in recoil other than those two. Giving 9mmP SMGs an additional point of RC over .45ACP SMGs doesn't make that much sense. Additional recoil penalties (such as double uncompensated) for the .45ACPs would be way too harsh.

(Says me, who has never fired any SMG.)

I would like to see the numbers on this, but having fired both a 9mm MP5 and a .45 cal UMP, the felt recoil on both was almost identical, which is to say, practically non-existent.

I think that the felt recoil between say a subcompact Glock 9mm and a subcompact para-ordenance .45 is quite substantial. That .45 will feel damn near like a .454 Casull because of it's extremely low mass.

However, I would tend to think most SMGs are heavy enough to make the felt recoil between a 9mm and .45 pretty much the same.

Raygun, any thoughts?

felt recoil is a completely relative/subjective concept.

Basically, felt recoil will depend on the weight to recoil ratio. So you have a 9mm SMG and .45 ACP SMG. Both fire 3 shot bursts and are the exact same model gun etc. You MAY have a slight increase in felt recoil on the .45 and I stress the MAYBE. Chances are 99% that the .45 SMG will be slightly heavier due to increased chamber pressures etc, even though it may be the exact same model. So this increased weight may cancel out any ACTUAL increase in recoil to the point that the shooter can not even perceive any increase in FELT recoil.

Actually, there are several ways to change the felt recoil on any (semiauto) firearm.
1: Alter the weight of the gun itself. this can be as simple as drilling holes in a wooden stock and adding lead weights.
2: Alter the weight of the bolt and carrier. This is less effective than the above but changes the overall balance point of the firearm less.
3: Stiffen the recoil spring. The mechanism that pushes the bolt back into place is controlled by a spring and by eating up more energy(because that is all we're talking about) you reduce the energy imparted on the user.
4-6 Personal grips exist today and are not nearly as resrtictive as the game makes them out to be, drilling holes in the barrel(a prosses known as Magna-Porting) forces gass to counter the movement of the gun, all this is without taking into account reducing bullet speed or weight(Force = Mass * Acceleration)
Also the .45 is a slower bullet than the 9mm but I don't know how much lighter the 9 is.

subcompact glock 9mm (glock 26) 20oz.
para-ordnance compact .45 (para-carry C6.45 LDA) 30oz.
do yer research.
recoil is subjective and .45ACP has a nice heavy push to it whereas 9mmP is lighter but snappy. a lot of 9mm SMGs in use by militaries use higher-pressure specialized 9mm SMG ammo (9mm +P+).
FYI, standard .45acp fires a 230 grain bullet at about 850 feet per second. standard 9mm Parabellum used by NATO fires a 115 grain bullet at about 1300 fps and the US military's M882 9mm fires a 124 grain bullet at about 1250 fps. but those velocities are from 5-inch handguns, ymmv.