Rechamber Options for the .45-70 32" SB-2 Barrel

[jkpq45]

Been doing some digging... wanting a more unique and powerful cartridge to take advantage of the 32" barrel offered for the SB-2 platform.  The options I've considered are listed below:

Seems like lots of folks are running their 45-70 Handis @ 42 Ksi, with 0.505" case head: 8412 lbf bolt thrust.  I'll assume this as a "safe" amount of bolt thrust that the SB-2 can handle.

1.  .458 Winchester Magnum - 0.513" base diameter at 62 Ksi = 12815 lbf bolt thrust.  WAY too much.

2. .450 Rigby - 0.589" base diameter at 58 Ksi = 15803 lbf bolt thrust.  WAY out of range for the SB-2 frame.

3. 458x2 American - wildcat, so can't find reliable pressure/performance data.

4.  450 Alaskan - having trouble finding reliable pressure/performance data.

5.  450 Nitro Express #2 - having trouble finding reliable pressure/performance data.

6. 450 Marlin - having trouble finding reliable pressure/performance data.

7.  (last but not least) .45-120, 110 or 90.  All options with their ups and downs--but it's definitely a proven concept on the Handi platform.

Comments or discussion are welcome!
jkpq45

[quickdtoo]

I use 500 S&W(52kpsi Hodgdon data)or 270 Win(65kpsi SAAMI) breech thrust for making comparisons. 

Tim

[jkpq45]

270 Win - 0.409" head diameter at 62 Ksi yields 8146 lbf breech thrust (wow!)

500 S&W Magnum - 0.480" head diameter at 52 Ksi yields 9410 lbf breech thrust (again, wow!)

[keith44]

The .450 Marlin, if I remember correctly, is basically a re-worked ballistic twin to the 45-70 for lever action rifles, do-able but just to be different, IMO not worth the conversion.


The .458 Win Mag is Brutal in a Ruger, and the 45-70 can be Hot loaded to within 300 fps of the Maggie (in a Ruger) both of which are a bit much for the SB2 frame.


The .450 BP express (instead of the .450 #2 Nitro) is likely to be the best bet but the express Rifles all push 300 to 500 grain bullets to around 2,100 to 2,800 fps (in original rifles, depending on barrel regulation)


The .45-90, 45-110, .45-120 etc can be interesting, but the price of brass for these is around $2.00 each.  Each (even the 45-70) can be loaded too hot for the Handi to handle)


Just my 2 cents

[bikerbeans]

If you have a 45-120 you can get close to 458 Win Mag velocities at lower pressures because of the big case, approx 118 grn h20 capacity.  Admittedly the 32" barrel helps with attaining the higher velocity.    The downside of this is a less efficient burn so it takes more powder to get a given velocity.  I have pushed 350 grain hornady jacketed RNs over 2,600 fps with i3031 and the brass was primed with Large pistol primers.  300 grain jacketed bullets in the 2800 fps range and 405 grain Rem SP at >2500 FPS have also been reported with the long barrel BC.   In my particular case, primers were not flatten and the brass ejected w/o issue.  My shoulder and forehead didn't fare as well.    
 
Since you mention a "proven concept" there are quite a few 45-120 Handis floating around and I haven't heard of anyone posting about any real problems with this chambering, but a 450 NE or 450 Alaskan would be cool.
 
BB
 
 

[knight0334]

If you have a 45-120 you can get close to 458 Win Mag velocities at lower pressures because of the big case, approx 118 grn h20 capacity.  Admittedly the 32" barrel helps with attaining the higher velocity.    The downside of this is a less efficient burn so it takes more powder to get a given velocity.  I have pushed 350 grain hornady jacketed RNs over 2,600 fps with i3031 and the brass was primed with Large pistol primers.  300 grain jacketed bullets in the 2800 fps range and 405 grain Rem SP at >2500 FPS have also been reported with the long barrel BC.   In my particular case, primers were not flatten and the brass ejected w/o issue.  My shoulder and forehead didn't fare as well.    
 
Since you mention a "proven concept" there are quite a few 45-120 Handis floating around and I haven't heard of anyone posting about any real problems with this chambering, but a 450 NE or 450 Alaskan would be cool.
 
BB

Yeppers!

Case capacity has it's advantages and disadvantages.  You can run much more powerful loads and keep pressures within working range of the gun with a larger case capacity.     But the disadvantage is working with loads that dont fill the case enough for consistent ignition.

My 300gr JHP loads are nipping the heels of the .460Weatherby Magnum in energy levels - yet are only a  few hairs above 40K PSI.