scott r;
As a rule of thumb and the proverbial “all else being equal” one can reasonably expect a 1% gain in velocity for every 4% gain in case capacity.
There are of course the usual flies in the ointment such as barrel length, diameter of the bore, twist rate, smoothness of the interior of the barrel and a few other factors that also can affect velocity and cause weird anomalies to pop up now and again.
We played with a newish Model 70 in .264WM with a 24” barrel that ran just a little slower than a 24” barreled .270 using the same weight bullets. While I realize that’s an apples and figs kind of comparison, that .264 wasn’t ever able to keep up with a 26” barreled 6.5-06 either.
As of this morning in the safe we’ve got two AI rifles, a .22-250AI with a 26” Douglas Premium barrel I put together to shoot coyotes and a .250AI with a 24” Ron Smith barrel we stuck together for our youngest daughter.
The case capacity on the .22-250AI is slightly more than a .220 Swift and it is capable of speeds similar to those we were able to achieve with a 26” barreled Ruger Swift, so no surprises there really.
The .250AI seems to not be happy when we’ve stepped on its tail and hasn’t given speeds much faster than I would have expected out of a non-AI. It redeems itself with sterling accuracy, very mild recoil and as a result is very poorly thought of by both local varieties of deer,
I will say that one nice benefit of AI cases is the almost total lack of case stretching which means trimming is nil. One still needs to anneal every 5 or so loadings though or the necks seem to want to split or that’s been the case with the .22-.250AI.
Someone on another forum stated one pretty much has to treat each rifle as an individual and the chronograph is likely your best tool for finding out what that rifle will do.
Hopefully that was some use to you.
Regards,
Dwayne