iwantadouble

The endpoint for reaming out the 45-70 is not the 45-90, it is the 45-120, these three share case head diameters.

The 45-120 is the 45/90 plus an extra 0.85" of case. These cases are available from Bell ~US$2.29 a shell (you even get to pay real NE prices for your shells).

Using the 450 No.2 NE 480gn projectile, seated to 0.458 gives 94gns of usable case capacity. With this you get to within 100fps of the 450 No.2 NE, at our Marlin lever gun intensity 42,000CUP limit.

You are way inside NE territory, you are there, no ifs, no buts.

Now I'm with 500 Nitro on expressing concern and counseling caution about reaming the 45-70 out to the 450 No.2 NE. I note that there is a distinct transition in reciever size across all manufacturers when you move head size from the lesser calibres (45-70 at 0.505" seems to mark the top end of these) to the 450 NE head size 0.545", let alone the 450 No.2 ~0.580".

To ream the 45-70 out to the 450 No.2 NE you must change the chamber from accepting 0.505" shells to 0.580" shells, thats hacking 75 thou from the very guts of a chamber, that's alot, as 500 Nitro rightly says that is eating into the meat, hairy stuff.

However, far be it from me to hasten you to your own destruction, but, I do understand you must if you must.

And if you must, compared to the 450 No.2 NE just how much metal would you be removing for a 45-120? Huge amounts less.

You aren't touching the chamber wall hardly at all are you, just extending the neck a bit, well more than a bit, oh OK alot, 1.15" past where you started and 0.8" past the longest chamber the manufacturers put in the gun.

NB. that this is 0.85" past where this urging bastard is prepared to go himself first off, don't listen to him, he just wants you to test the water with both of your (not his) feet.

Off the shelf components, readily available reamers, real NE DG power all in a package you can regulate to your own satisfaction. Sounds good, real good, almost too good.

If the above fantasy, reaming the 45-70 to 45-120 (not forgetting your freebore), works out and you succeed then congratulations you will have a real 450 in a 7.5lb gun ........ a raging pitiless recoil monster, make it weigh 11.0 lbs before you detonate it even once, repeat, even once.

AR2201
The sleep of reason breeds monsters

Ah but visions you will see