I got this straight from the horse’s mouth, the Director of Customer Service. I had 4 email exchanges where he was kind enough to answer specific questions related to the Savage impulse rifle that boils down to the following:

1: There is only one aluminum receiver and bolt no matter what Savage impulse model.
2: There are two barrel extension sizes, one for small shank and one for large shank.
3: The barrel extensions will interchange into that single receiver, as you would expect.
4: Small shank calibers are: 243, 6.5 Creedmoor, 308, 30-06 and 300 Win Mag
5: Large shank caliber is 300 WSM
6: All savage 110 barrels fit the appropriate size barrel extension.
7: That means there is universal interchangeability between any Savage barrel made with a the new Impulse rifles and the 110 series with a large and small barrel extension

The only bad news out of any of this is that they don't know when they'll have barrel extensions and bolt heads for sale. I can only hope that it won't be too long a wait till they make the extensions and bolt heads available. I think if tghey did that, they would see an increase in sales. I think if they made this information know they would see an increase in interest.