• *The discussion of the creation, fabrication, or modification of airgun moderators is prohibited. The discussion of any "adapters" used to convert an airgun moderator to a firearm silencer will result in immediate termination of the account.*

One suppressor for 2 barrels

From my experience, yes there should be no problem. There might be a minor degradation of the suppression performance, but one caliber difference shouldn't be noticeable IMHO. Many DonnyFL mods are sold for two calibers, i.e. 177/22, 22/25, 25/30. And some actually prefer to step up the mod one caliber to avoid pellet clipping. I personally have no problem using 30 cal mod on 25 cal rifle, works just as good. But I don't have experience with this specific DonnyFL moderator model, sorry.
 
I’m getting an impact m4 25 caliber sniper I also have an existing 30 caliber slug barrel from my older impact . I’m thinking of getting the Donny Yakazuna moderator for it if I use the 30 caliber moderator on the 25 caliber barrel will it work effectively.
You can always buy the .30 moderator, then purchase additional.25 cal middle sections. When you change caliber just change the two or three mid sections. Does make a small audible difference. Just don’t forget to swap the.25 when going to .30 unless you want to try pellet resizing on the fly 😉