Sorry to resurrect an old thread but I have a 21" .400 Whelen and can confirm that very little is lost with a shorter barrel. This round is extremely efficient so it doesn't take much length to get everything burned it seems.
My little rifle can comfortably do the following with zero visible pressure signs (doesn't mean I am not over 60K....just that it isn't showing up in my brass in any way):
300 Hornady at around 2,400 +/- (I believe RL 10X on this, will check notes and edit if different)
300 TSX (I think this could be a very capable do-all load) @ 2,350 +/- with H4895
360 North Fork (seems to be a tremendous bullet) @ 2,225 with RL10X
400 Hawk @ 2,140 with CFE 223
Will do some testing this summer to see what happens at 90 plus degrees. May have to back off some if using this outside my typical fall Montana temps.
I believe my 360 NF load has some FPS left on the table but I got good accuracy and very manageable recoil so left well enough alone. When I first worked up the load I only had one box of 360s. Spitting out hard to obtain imported bullets at $2+ per seemed like a poor choice just to gain a few more FPS. I have since obtained more bullets and have made plenty of bad choices so will see what CFE can do with the 360 sooner than later. I am sure all my future hopes and dreams of killing large beasts will hang in the balance of whether I can break 2300 fps with the 360 NF (*sarcasm*).
I have been able to get acceptable accuracy with everything (1"-1.75") except the 300 grain Hornady. I get a few fliers with that stubby little thing that will turn a nice 1.5" cluster into a 4" hair puller . I regulated my open sights to that bullet and will just use it for offhand practice since midway had a run of 2nds for a tremendous price. They feed like greased trout in my rifle and, even with the fliers, are plenty accurate for offhand 100 yard shooting of pigs or whatever. They thump enough when you pull the trigger that they should work for building muscle memory for practical field practice
I believe Mart or someone on the 24HCF thread had feeding problems with the 300 Hdy but my rifle is the exact opposite and feeds poorly when cartridges get too long. I have been able to resolve my feeding issues with tweeks to the mag box.
I have taken just four deer and an antelope with the rifle and all with the 360 NF. If conditions are right I may try to poke a cow elk with the 300 TSX in the next week or two but have some other rifles I want to hunt with so not sure who will be on the dance card.
A gentleman recently sent me some cast bullets to try out as well as some .412" lead round balls that he shoots over a very light load of pistol powder for a virtually silent small game load that is accurate in his rifle. He also has loaded shot to make his .400 into basically a brass cased .410 shotgun. I encounter a lot of grouse on my elk hunts...a few of these in a coat pocket could be just the ticket for camp meat.
It is all nonsense ofcourse, but my .400 has been my hands down favorite rifle project. A .41 Mag, a .410 shotgun, a roundball shooter, deer slayer, moose poker and buffalo stomper all in one little package with cheap brass and manageable recoil.
