1. The .404 Jeffery case holds about 115 grains of water, is long-necked, and is zero-freebored.
2. The shorter and fatter .423 Lapua case holds about 120 grains, has a caliber-length neck, and 0.4000" freebored.
Then:
3. Seating a .423 bullet 0.2000" less deeply into the case will give the .423 Lapua about another 7 grains of water capacity (or equivalent increase in powder space) over the .404 Jeffery, if my numbers are right (7.1 grains, to be unnecessarily precise).
So:
4. The .423 Lapua if loaded long nosed with a long bullet will have about 12 grains or 10.4% case volume advantage over the standard .404 Jeffery.
And:
5. If the .423 Dakota-Lapua is really only 2.5" long, then it will have less case capacity than the .404 Jeffery?

Sumthin ain't right here! Oh, I forgot, the Dakota-Lapua probably has all that beautiful Rigby/Lapua body taper blown out for some case capacity increase, maybe to equal the .404 Jeffery in a shorter round? Should be interesting to see.

Guess I'll have to get on the phone and see if anybody knows how long the .423 Dakota Lapua really is. Maybe Dave Kiff can talk now that it is post Shot Show 2006.

Anyway, I have a homemade .423/.338 Lapua Magnum still in the rough, but shootable by the weekend, consisting of:

24" McGowen stainless No.5 sporter of 10" twist
Dakota 76 African action still in the white
MPI stock that required about 1 pound of Steel Bed, JB Weld, crossbolts and pillars to reinforce it (MPI only as an expedient)
Talley bases and rings that overhang the rear of the ejection port a bit to fit the scope
Leupold 2.5x-8x with Boone&Crockett reticle

I'll just load my maximum .404 Jeffery loads of Varget as starting loads, 88 grains with 340 grain North Fork, and probably move on up to 100 grains of H4350 Extreme with 380 grain North forks, and maybe over 95 grains of Varget with the 320 grain GSC HV.

This may be the Ultimate African Sheep Rifle.

Actually:

A .404 Jeffery with bullet base 0.6" deep has a water capacity of about 115 -21 = 94 grains.

A .423 Lapua with bullet seated only .4" deep has 120 - 14 = 106 grains water capacity.

12/94 = 12.8% advantage of a long nosed .423 Lapua over the .404 Jeffery.

Well, that is the general idea.

Esoterica for those of a peculiar bent, unlike JTG.

Over a pound of JB weld....I was under the impression that MPI makes a decent stock. Is all this really necessary? Anyhow your project sounds like a fun one. Just out of curiosity, how much different will this round be than a 416 Weatherby?

looking forward to the range report sir...

BS,
Will do. First up: 340 grain North Forks and Varget Extreme, just to get my bearings with a known bullet I have used before in the .404 Jeffery.

Roscoe,
This is the first MPI stock I have used, unfortunately, and I cannot recommend them. Mine came with the web between the magazine well and trigger well already cracked. I cannot blame UPS for the rest of its misshapenness however. But I'll get by, with close to a pound of epoxy and steel. Another shop mule for now. Don't expect pretty pictures anytime soon. Way different from the .416 Weatherby.

Some would even say the .423/.338 Lapua Magnum is downright "peculiar."

Way to go rip!!
jeffe

Thanks, Jeffe. Your stock work is way prettier than mine, judging by that .470 AR lately.