Yup you ca stretch it more and fit another 38 round. But,only if you stretch it enough that it becomes a K frame.
Get a set of calibers and check it out.
Some manufactures make a near J frame 6 shot J frame diameter cylinder. But their chambers are farther towards the center. S&W can not move their chambers towards the center without reducing the size of the ratchet, which means moving the hand inward, which means making the trigger and hammer narrower. It also means moving the barrel down in the frame and redesigning the yoke to clearance the lowered barrel in the frame. Simple HUH?
PS it also means a heavier double action trigger pull because the ratchet is actually a gear so it takes more leverage. Just like on a bike when the rear gear is smaller it is harder to petal than when it is larger.
Well, it's after 10 PM and my hip is killing me, so I'll have to wait at least until tomorrow to take a photo of my Rossi 462 with a K-frame. And I already slammed down my thoroughly-vetted and heavily regulated Opioid, so if I fail to hit all points or don't make sense, we know why.

Anyway, I disagree. Even the S&W Model 73 was smaller than a K but larger than a J. Since they are nonexistent for us mere mortals, I can't measure one to see the difference. But as I mentioned, the Rossi an older one from the 1990s, is about as close to identical to a S&W in design and construction as you're likely to see. For one thing, the chambers are not "closer," because it's too big for any molded J holster, meaning the cylinder is definitely larger than a J. But it's also too small for a K holster. And I popped the side plate once to see what the fuss was with the recall, and I'm tellin' ya, it's a CLONE in there. It has all the same parts.
For sake of adding to the measuring conversation, I have a couple of Taurus Model 431s, 5-shot 44 Specials. They are nearly identical to a K-frame! Might be off a millimeter or two, but not enough to matter. They fit in all my K holsters, including my molded Israeli Front Line brand.
As far as messing with the hand-ratchet combo, I'm sorry but I don't buy it. If I remember, I'll just photograph a J, a K, and the Rossi together. Good night, y'all!