BB/Pellet Shells

To be honest, I use both types for pellets and I haven't noticed that much of a difference when testing with a chronograph between either of them (pellet or bb shells), irrespective of whether the gun had a rifled or a smoothbore barrel.

I have noticed slight differences in the 'batches' of cartridges being made though, some of them have a clear fake bullet to case line on them, others completely smooth, some have quite a thick base rim, others have a thinner base rim, the silver pellet cartridges are thicker (a larger diameter)than the brass bb cartridges and that may play an important part in reducing or even stopping gas blow past effect when the projectile leaves the cartridge and enters the throat of the barrel (the tightness of the cartridges fit into the cylinder should stop the CO2 from escaping back through the cylinder). So whether these differences extend to internal bore size differences too ? I really don't know.

There's so many factors involved that it's difficult to actually set a hard and fast rule, I prefer the overly straight forward 'suck them and see' principle, give them a go, ultimately you'll be able to tell for yourself if they have the same sort of accuracy.

The most accurate Colt SAA I've got is a smoothbore barrelled one that I use with pellets, plus I also use both types of cartridges in it !

The grommets are identical in size irrespective of whether they are pellet or bb shells, they're totally interchangeable, if they was any difference you wouldn't be able to successfully hold a bb in a pellet shell's grommet. It maybe different with other guns but this is the case especially with the Colt SAA shells and the Remington 1875/Crosman Cowboy shells. A lot of other shell loading revolvers have rear loading pellet shells and front loading bb shells (Webley mkVI, DW715, etc), so the question doesn't really arise.

The job of the cartridge is simply to get the projectile from the base of the cartridge (where the power valve outlet is) to the throat of the barrel (commonly referred to as the forcing cone or breech). It just gets the projectile up to speed before entering the barrel and engaging the rifling (if present). The accuracy of the projectile and any rifling are imparted by the barrel, the cartridge is just the 'launch pad' to start the whole process off.

Without getting into a protracted and pointless debate, the obvious answer is to try them out and report back with YOUR findings, as I have previously stated, there's too many differences between the many batches of Colt SAA shells to make a definitive answer without another member finding fault with your opinion.

(I want to point out that I don't disagree with the information that CaptDAR has stated, in fact I'm in total agreement with him, as it just points out the differences between certain batches of shells ! His seem to be one way and mine seem to be another, which shows the variety of differences available in cartridge shell sets).

I know ! It's amazing how different they are. I'm glad that you have managed to find the 'sweet spot' with the Colt SAAs.