I see where a lot of people are taking their .45-70's and turning them into .45-90's and .45-120's. ... is there anything to be gained by by this if you're using smokeless powder?
<sigh> Firstus, you be lookin at this all wrong! Gaining anything is not the point!
SIZE DOES MATTER!

If something's big enough, that's what gets all the attention! How well you use your equipment is never really remembered by those who admire it's proportions! I know this is hard to understand for the majority here; those suffering through life with their iti-biti power tubes. They must be able to milk out the last bit of performance from the tool in hand... so to speak. But for those of us fortunate enough to become endowed with a truely magnificent weapon of gigantic proportions... well, we garner swagger rights around all who see it.

Fortunately for the majority of men, their deficiency can be eliminated by a simple and inexpensive operation. You to can join us and be a "man among men!" Several here are preparing to undergo this enlargement as we speak. And there is one, fittingly called "Long Tom," who intends to take this matter to a
length and
circumfrence yet untried!

Wait! what were we talking about!?

Oh yah, the 45-120...

I to struggled with the "practicality" issue for a bit. But I was finally able to convince myself that practicality and need had nothing to do with this project. Those virtues had to be abandoned at the outset. If even a bit of one of those thoughts remained, noone would go longer then the 45-100. Especially if they read the outstanding range report a member (who was that Tim?) did on his experimentation with that cartridge.
Nope, it's mostly about "Shock and Awe" and it's just plain fun playing with loads!

For example, I believe my starting load with the 405 gr. bullet is faster then a well known, loaded to the gills, factory 45/70. And that company makes money selling those or they wouldn't be loading them! So there are people out there who want moremoremore from the 458's but don't want WM's or Lotts. Some of us just got to be different!

So while "gaining" anything is not the point, it can be a by-product. But being the conservative, practical type by nature, Ima thinkin that a 28 inch barrel in 45-100 would be perfectly suited for all my big-bore needs...

Then I'd have a 22" - 45/70, a 28" - 45/100 and a 32" 45/120!

...

... wait...

somethings missing ...

Geeese!

That's quite a gap there on the low end...

Ya know what I need!?

A 45/90 in a 24 or 26" barrel!!!

And...and ya know what!

a 16" 45 Colt barrel!!!!!! ohboyohboyohboy!!!!
