I would guess this has been done a long time ago...
I had the thought of ...say .308 Win in a long action to gain extra long loading
(Beyond 2.8"l . Who is doing this or is this some galactic shattering information? Is there some super secret society I must join in order to master the un-speakable esoteric works?
Just me wondering what if ???

I think you can do it but there's just not much point. The only reason to really load that long is to use a heavy bullet, which will be mitigated by the powder limitation of the case. Most short actions these days will get you to 2.9 -2.95 anyway. If you have a long action just use a .30-06. I have run across a couple of guys running single-load .308s and shooting the 208 ELD but they're also using a 30" barrel. To each his own, though.

I've loaded 308 Win for customers on a long action many times. Usually the gun smith will custom throat the chamber/lands to the bullet you want to shoot. I've loaded for several comp shooters who run a 200-220 grain bullet in the 308 seated out really long. I recently did one with a 200+ grain Berger running almost 2800 fps in a long action, long heavy barrel rifle. I think the COAL was around 3.100". It was pretty nice.

Yep understand that all too well.
I'm thinking along a couple of diverging threads.
First is using the Remage type barrels. You could take it either direction on a single platform.
The other is being able to maximize the potential of any of the shorter cartridges.
My thinking runs along some of the new 6mm or 6.5 's that are low enough recoil to allow you to stay in the scope yet get higher the higher velocities of the bigger cartridges.

My internal ballistics computer tells me something like a shortened 7mm Express with a long neck would be a sweetheart ? Probably a duplicate of the 7-08 AI ..??

You would need to select the right 6mm or 6.5mm case. The Creedmoor case already seats the bullet out long. So going to a long action in either of those, would yield some extra room, but not a lot to be worth a long action build. You can easily modify a short action, long throat the chamber, run mags with longer COAL, and you would be good to go.

Perfect name would be the 7mmNeedmoor

Short cartridges on a long action can also present its own problems in feeding. I had an 03A3 that was rebarreled to .243 and if you didn’t stack those .243 in the right spot they would jam. Everything would tilt forward, then you had to open the bolt and rearrange the bullets. I’ve saw this more recently on a long action 257 Roberts. Although the issue is not near as bad, it is there.

If you've got a long action, might as well load a 6.5-284. If you're wanting a 6.5mm

Funny you mention 6.5/ 284
After thinking about it the .284 fits the bill for 7mm
Little bigger than 7-08 not as big as 7mm express.
As usual ...already been done!

Last 6 rifles that i have built have been on long actions with short action cartridges.

.284 Win
.280 A.I.

Neither one is a bad choice. I've got experience with the .280 A.I. and love it. Judd has experience with the .284 Win.

I’ve built many SA rounds on long action. The 7 and 300 wsm really come alive on a long action. To build a 22-6AI if your going to run heavies needs a long action. I’ve also built 308 and 260 on long action running heavy pills. The thing is running a long action alone isn’t the answer to take advantage of case capacity. The barrel should also be throated for the longer projectiles. Imo Unless your building with very specific weight specs like a true mountain rifle it doesn’t make much of difference to me. I like building off LA’s

284 win is ballistic twin to the 280. Little bigger than 7-08 would be 7x57, which is an awesome round especially AI’d