I’m GMing a campaign set in the Western Montana/Eastern Idaho wilderness with an emphasis on survival. The fellas I’m GMing for have been curious about using calibers (especially hunting calibers) not included in the core rulebook such as 30-06 Springfield, 30-30 Win, 270 Win, 45-70 govt, 357 mag, 38 spl, & 9mm. Mostly we’re looking to spice up the game and make it a bit more immersive.
If anyone have any ideas on on how these could work damage and special effects wise, we’d be thrilled to hear it. Also, if there is a spreadsheet out there somewhere with more variety in the way of real-life ammo and weapons that would be cool too.
With most weapons doing 4 - 6 CD as a base I would say it’s difficult to accurately represent the difference between many ammo types.
I would say for rifle ammo (based on quick search on muzzle energy)
30-06 Springfield and 270 Win would be equal to .308
30-30 Win is equivalent to .45 in a combat rifle
45-70 govt would be 7 CD and vicious (balanced by fewer receiver mods)
the .38 in game is probably .38 spl
9mm is equal to .38
.357 mag is equal to .45
alternate .357 mag is 4CD vicious
Check out the Wasteland Necessities thread on this very forum. It compiles most of the weapons and equipment from the Fallout games into one sourcebook. It is of course unofficial but it is a very nicely done.
Seconded @Corwyn suggestion of Wasteland Necessities, it’s an essential document. I will also sometimes convert weapons & equipment listed in the Fandom Wiki. It’s not perfect, but its better than nothing. Really hoping we get to see some new official material this year.
In response to your question though, 9mm .38, .357, and .380 are all technically the same caliber. There are differences in their relative penetration though. .380 ACP has a psi of 21,500, while a 9mm has a psi of 34,000 and also the barrel lengths from the weapons they are fired from affects this.
That said, I don’t think the game cares about variations of precision that much, so what @Lane wrote is probably the best rule of thumb.