I’d like to get a caliber specific suppressor for my 40S&W & 10mm pistols. I don’t have any 45 ACP pistols, so a 45 suppressor seems like a waste given it would allow extra space around the flight path through the suppressor and it would likely be larger in diameter. However, I can’t find one. Does anyone make a 40cal / 10mm specific suppressor?
The additional bore size is a good thing in my experience because there’s a little extra margin for error to prevent baffle strikes. I think we shot a 45 can on a 9mm, and to my surprise the additional bore diameter didn’t translate into a noticeable difference in suppression.
A 45 cal can would have more versatility, but I understand if you want a caliber specific model.
The Silencerco Osprey used to be made in .40 but I believe it’s discontinued.
To the shooter, which is all most people need to be concerned with. Sometimes there is a difference to the shooter, other times, nil, as you experienced. With equivalent designs, there will be a difference at the muzzle, but it probably doesn’t matter. Most .45 cans are longer than their 9mm stablemates to mitigate that.
OP, I think YHM used to make a .40 can. Honestly, I’d probably follow MarkM’s advice.
I got lucky and listened to someone on here years ago and got a .45 can instead of a 9mm. I use it on everything and it came with a FB Spacer for my PCC and an extra 16X1RH piston for the HK45T I just picked up. Sig SRD45 I think it is.
Get a .45 can with interchangeable front caps, then get the appropriately sized front cap, or have an undersized cap bored out. A caliber specific front cap helps with metering performance but .45 and .40 are so close I don’t know if the juice is worth the squeeze.
A 45 can is ideal IMHO. I like the tad larger hole for a touch of gas to escape and I run a 45 can on multiple PCC guns in 9mm and they work just fine. So a .40 would work very well and if you ever get a .45 your GTG.
Hell, I run a 338 LM can on 300WM and 308, I feel the over bore is exaggerated as an issue. Especially if you have not shot a lot of suppressed weapons.
PB
Well, I might have to get a 45 caliber can, but I was just hoping that someone would make a 40 caliber one. Given how many manufacturers there are and how many 40S&W/10mm pistols there are, you’d think that at least one manufacturer would make them.
I’ve got a new in the box SWR GS40 that I’d sell.
I think Yankee Hill made their Cobra in .40 at one point.
I found that B&T makes one, but it’s for the APC10/40. 
Rex Silentium will make you a MG series can however you want it.