Wanting to keep a larger clip quantity. In most rifles you get 4-5 in the clip with a .473" case and 3 with a .532" case.

How difficult would it be to lengthen a 35 Whelan case to 2.850"?

Without dragging out the mics I suspect you would end up with a very short neck if it could even be done, and thats no good...

I suggest a drop box if you want more rounds in the magazine. Most bolt actions will take 4 338-06's down and thats plenty IMO...but you can extend a std. box to as many rounds as you want, or go with a drop box for 5 and perhaps 6...If you want more velocity then go with a Ackley IMP. or a drop box .338 Win.

ar corey Not sure where you are going to get a custom made 06 type case that is 2.8 inches long. There is a case that is a little longer than the 06 but the same diameter. That is the 9.3x66 or the 370 Sako mag. The case is 2.6 inches long. You could easily neck the 370 down to 338 to gain a little more case capacity over the 06 case.

2.65-2.68" is about the longest I've found. Problem is unless you are going to go with a long magnum magazine the bullet takes up the majority of the larger case. I have a 400PDK that uses 2.65" 06 basic. However if you take the much shorter 400 Whelen case and load it to the same OAL as my net gain is only a couple of grs.

To me the 370 Sako is a waste. If you take a 9.3x62 load it to the same oal as the 370 same pressure you basically give up nothing. Since the 370 is designed for the 06 length mag all that extra case is full of bullet.

Longer case, use the longer 3.6" magazine to get the most from the bullet/case combo. As noted, nothing is gained by using the shorter 3.4" magazine length.

9.3x66mm/370 Sako Magnum was 'built' to satisfy the African countries that require a minimum projectile energy level for DG hunting. It as well would do much better with a longer magazine length and the bullet seated no deeper than the shoulder to shoulder/neck junction depth. But these days you get a 3.4" or 3.6" magazine and nothing in between from the factories...

Bent Fossdal, not sure if he still posts here, built a line of long carts based on the 9.3x74 case.
He chucked them in a lathe and turned the desirable rims.

The Howell line up of cartridges is close to what you're speaking of. They are simply elongated .30-06 cases of 2.6", and use a 3.6" or better magazine. You can get five down of those in an action like a Sako, giving you six total shots. I'm not sure why Ken Howell didn't go ahead and make them "full length", or approximately 2.8" since the magazines they are used in would as easily accommodate a cartridge of that length.