I was juggling this idea around for awhile and just got off the phone with my friend who I just found out started hunting axis deer with a new rifle a 240 wby mag here in Hawaii. He has around 20-22 animals with it and all got hammered. He claimed from 10 yds to 550 yds all one shot kills. He started using Hornady 100 grain soft points and now uses Hornady 108 eldm’s. He says even the big bucks crumble, if not running only 20 yds or so. Kills just as good as his 30-06 with 165 gr soft points and doesn't drift as much in windy conditions. I would definitely take his advice as he killed dozens of axis deer each year for decades.
I’ve had a 240 Wby for a little over 20 years. It shoots flat and hits about as hard as your going to get out of a 6 millimeter.
I’ve used the 95 grain partition with great results but switched to the 95 grain Ballistic tips for deer with no complaints.
I just recently re barreled that West German made rifle with a 7.5 twist Krieger and plan on using some of the heavier Bergers. Incidentally, I have hammered quite a few large ground hogs and foxes over the years but wouldn’t take it into a prairie dog town and toast the barrel.
I have a 240 wby, but haven't used it on a deer yet. However, I've seen dozens of deer killed with a .243, and killed a few myself. It performs admirably on whitetail. It is plenty of rifle, and the additional speed you'll get in a 240wby should only make it that much better.
I've owned 3. I've found that any good 90-95gr bullet and 54gr R19 always seemed to work just fine. I have a church member who uses his old German Mark V 240 Wby ( for past 40 yrs here and in Utah/Idaho) with the Hornady 100gr Interlock Boat Tail on mule deer and even big elk. I think he use IMR 4895? Anyhow, I've used a lot of 6mms through the years...6x47 (222mag/6mm wildcat) 6mm Bullberry (30-30 Imp/6mm) .243, 6mm Remington and .240. The 240 Wby is by far my favorite 6mm. It runs right alongside the 25-06. And yes, I know a few guys here who use the 25-06 on elk too.
Last whitetail I killed was a small doe at about 100 yards. 80gr Barnes TTSX with 52gr IMR 4831 running at about 3600fps. She dropped like a rock. Entrance hole was small, but the exit was about the size of a nickle.
I would personally go with a 6mmAI for a fast and easy .243 rifle. Mine is super accurate shooting 87vlds @3500.
Jumping bullets .150 or more makes it very hard to tune it down to sub moa. If thats good enough for you then shoot whatever.
Not that a weatherby can't shoot well and some do the ridiculous freebore makes it more difficult.
Fireforming the 6mm is easy. Just shoot factory 6mm through it. Mine shoots sub moa while fire forming and .250 hand loads. Coyote slaying machine to 800yds.
If you don't want the pain of brass availability these days along with rack ammo, and you're a hand-loader you might consider the 6mm-06 a near ballistic dead ringer for the 240 Wby Mag.... you've got; .25-06 Rem .270 Win .280 Rem and of course .30-06 brass everywhere. A couple of guys I knew went with the 6mm-06 AI and found it to be an amazing cartridge. Just thinking out loud guys. Cheers.