Btw!.............If one were made and using identical reloads, I`d put money on a 16.5" tubed 270 WSM to achieve better velocity #s than a 24" barreled 270 Win.
A 24" or 26" tubed 270 Win, will in no way match the velocities from a 23" 270 WSM.
With certain cartridges, the shorter and fatter cartridges with greater powder capacities, will not only match, but exceed the performances of their standard longer barreled counterparts.
uuhh....Squeeze, I'm afraid you're wrong on this....there is only 10 grains difference in powder capacity between the cartridges.
..........Are you sure???
.....If the 270 WSM is anything like my 300 WSM (a shorter 7.5" barrel vs the 24s), there should be a loss of only 4.5% in total velocity. Granted, I have no personal chrony experience with 270 WSMs. But if I were a betting man and based on what my 300 has done and from experience, I`ll wager on a shorty 16.5" tubed 270 WSM to exceed the performance of a 24" 270 Win and give some odds in the process too.
If you were to deduct 4.5% from the average 24" barreled 270 WSM velocity #s for any given bullet weight, those #s should still average above 24" tubed 270 Wins.
A 24" 270 Win vs a 16.5" 270 WSM, is almost the same comparison as a 24" 30-06 vs a 16.5" 300 WSM. But guess what; I have gotton 26" tubed 30-06 AI specs from my 300 WSM shorty, which is certainly better than any 24" 30-06.
Sure! It depends on the individual rifle characteristics, slower bores, faster bores, etc & etc. But for an across the board average, I`ll take the 270 WSM with a barrel 7.5" shorter, to out-perform the 270 Win with the longer 24" barrel. Unfortunately, there are no shorty 270 WSMs floating around out there to find out for sure. Though that would be an interesting match-up.
That extra 10 grains of powder capacity that the 270 WSMs have over the 270 Win, like the 300 WSMs have over the 30-06, can more than compensate for losing 7.5" of shorter barrel length, especially using todays more modern hi-tech granulated powders.
4.5% of say 3000 fps is 135 fps; 135 divided by 7.5" = 18 fps (per inch). My personal chrony findings with my 300 WSM vs two 300 WSM 24" barreled ones, averaged right in-between 16.3 fps and 19.4 fps per inch for all identical loadings tested which included some lower charges, some medium and maximum charges. The loadings also included various bullet brands and bullet weights. The days of losing 40-50 fps (per inch of barrel length) for "most" cartridges,,,are over and done with.
Although I cannot prove it to be sure, my gutt feeling based on experience is; that if ever tested, a shorty 270 WSM wouldn`t be too far off the mark and/or, very capable of doing exactly the same, as what my own 300 WSM has done.
But! You know what they say about feelings. Feelings are merely feelings, until they can be proven as fact.