Jim Bell did it with a barrel on a 7mm-08 having been a long time user of the 7mm-308, the wildcat before Remington brought out the 7mm-08 as a factory cartridge. I recall Jim starting with a 29" barrel and cutting it back an 1" or so at a time. Even with the 7mm-08 using faster powders, the longer barrel lengths produced more velocity.

I personally feel that there is not much point in using a magnum cartridge unless you are going to wring out the best ballistics you can. Take the 7mm Remington Magnum, many decry the fact that they struggle to better a 7mm-06 or 280 Rem (the same cartridges really) or even better the 7mm-08 by much, and struggle to get to 3000fps with the 160gr bullet. Problem is that as a poster here has said, the Americans pretty well standardise on a 24" for everything. The magnums burn slow powder and a 26" barrel gives the best between handiness and a tube that will burn the slower powders giving top velocity.

I could easily get an honest 3000fps with a 160gr projectile from my 26" barreled Schultz and Larsen 7x61 (belted 7mm magnum)and the factory rounds with the same weight of bullet went close to their advertised 3100fps. I could get 2900fps out of my 24" barreled 7mm-08 but only with a 140gr and I can hit the 3000fps mark with my 6.5-06 in a 24" barrel but again only with a 140gr.
The 7x61 and its 26" tube ruled supreme with any combination.

For long range shooting at game where the magnums can shine, a 26" barrel is definitely an advantage. For those that say only a 24" is needed then why not go 22", 20" 18", there will always be someone who defends a shorter and shorter barrel and maybe for other reasons such as lightness, handiness in vehicles or the bush, but when it comes to velocity in any given barrel with the best powder for that cartridge, longer barrel length does count.