In general, I use the following formula as a starting point for my MINIMUM choke diameter:

D = 2 x [ r / cos(30) + r ]

where D = minimum diameter of the choke, and r = radius of the shot (i.e. half of the shot diameter). This formula actually gives the diameter of the MINIMUM circle that 3 pellets laying in the same plane would fit into, i.e. 3 pellets touching in a triangle shape.

It's not PERFECT, but it has always worked for me. I pick a buckshot size, then pick a choke according to this formula, and bango, I have GREAT patterns, so why keep messing with it?

So, for example, 00buck has a diameter of 0.33".

D = 2 x [0.165/cos(30) + .165] = 0.711" diameter (not counting the thickness of the shotcup walls). So ultimately you need something in the 0.710"-0.720" diameter chokes for 00buckshot.

Now, for your example, #4 buck, with a diameter 0.24", you're looking at 0.517" diameter for 3 pellets to come out simultaneously, OR 0.579" for 4 pellets to come out simultaneously (use cos(45) instead of cos(30)).

If you're talking about #4 SHOT (not buckshot), then you're talking about a different dynamic (acting more like randomly packed micro shot, rather than tightly packed/organized macro BALLS), and you can use a VERY small choke (I use a 0.660" for turkey with 5shot, works fantastic).

Back calculating, I would expect #1 buckshot to pattern poorly in a 0.660", a #2 buckshot to be marginal (maybe lucky, maybe not), and #3 buckshot to be the max shot size for that choke.

So yes, you should be fine with a 0.660" choke for either 4 shot or #4 buckshot, but not much larger.