Wildcat .303 and 7,62R
Everything old is new again.
Both cartridges have been wildcatted into all the "common" hunting diameters( .22,.243.25, .26(6,5mm), .270, 7mm, 7,9mm ("8") and .35 for the .303 are some of the conversions. There is also a .303/375 as well ("9,5mm").
And when these are used in a Mauser actioned P14 set up, can get the same performance as American darlings such as the .257 Roberts, the 358 Winchester, the .220 Swift etc.
The Finns (and the Russians) have a more limited field, as "Wildcatting" is a Gunsmith thing, and the ammo is then mostly factory made...but there is a 5,6x54R, a 6,35x54R, a 6,5x53R, a 7x54R, a 8x54R and a 9x54R.
Expanding out in both cartridge cases is the lesser of the wildcats, there being (in both) an 8mm (either .323 or .328), a ".35" ( .354/8 or 9mm) and a .375 ( or 9,5mm)
If one adds the .410 Indian Musket (Ball) cartridge, one could say as well there is a ".420 "or so as well.
Wildcatting on your own...stick to the proven and tried calibres, for which barrels are available.
.444 Marlin cases are also slighlty larger than normal .303 cases ( .467 vs .455) but under the size of Russian cases ( .485 or so)
Both Lee-Enfields and Mosins have been made into rifles which feed 45/70 (much larger rim, .600 vs. .560 for Russian, and .530 for .303)
So one could add a whole slew of .45/70 based cases ( which are about 56 mm long to fit in the magazine) in different calibres ( .33 WRA, .40/65, even 8x52 Siamese or 8x56R Mannlicher...These are all factory cartridges, so it begs the question,
With so many Factory calibres (current or obsolete) which could be used in a action (SMLE or Mosin) Why Bother wildcatting???? Re-invent the wheel, maybe?
Unless you have a real Klunker of a rifle ( a Bubba job, too far gone for Restoration) I would consider a Wildact on either of these actions to be an excercise in Futility...the pressure limitations, the wide range of existing Factory cartridges already around, and the work that may be required to assemble your own personal .395 Rimmed Lee Special, or your 10,25mm Khazakstan Express...just the cost of the barrel would put the rest of the expense in the shade....
Regards,
Doc AV
AV Ballistics.