As someone that owns two 300ultramags and has owned a 300 wby I can tell you that I much prefer the 300ultramag.When loaded to equal pressures the ultramag produces more velocity as it should considering it has a larger capacity case.My ultramags also have the edge in accuracy over my weatherby mark 5 in 300 wby mag.Actually neither of my weatherby rifles were any more accurate than my factory 700' s in spite of the extra cost.My ultramags are customs and do cost a little more than the weatherby but accuracy is much better than either of my weatherbies.I have no experiencewith the 300ultra short mag but since their capacity is much less than the ultramag they will produce they do produce at least a couple of hundred feet per second less velocity.