Your Rossi 1892 is plenty strong enough for any load up to .44 magnum rifle velocities. Marlins, Rossis, and Henry Big Boys all are offered in both .44 magnum and .45 Colt.
A bonus with .45 Colt is that it's greater case volume (than .44 magnum) allows you to achieve magnum velocities with the same bullet weight at lower chamber pressures.
Typical factory .44 magnum ammo will have a pressure around 34000 PSI while equivalent velocity .45 Colt handloads will be around 25000 PSI (with equivalent bullet).
But, I hear ya when you say that you just want something over 1000 FPS. I have some .45 Colt rifle loads loads from the Lyman 48TH Edition Reloading Handbook.
For cast lead bullets:
250 grain #452664 Lyman cast Cowboy bullet from a 16" barrel (19" or 20" barrel will be slightly greater velocity.) - factory load
- 8.2 grains Unique / 1101 FPS. (931 FPS in 7 1/2" revolver) (8.0 grains of Universal would be equivalent)
- 10.5 grains HS-6 / 1066 FPS
- 7.5 grains PB / 1010 FPS
- 6.5 grains Red Dot / 1005 FPS
- 6.2 grains Titegroup / 1020 FPS
- 7.4 grains 231 / 1031 FPS
With a cast semi-wadcutter of 255 grains (Lyman #452424) velocities are similar.
The above handloads all seem to reflect a very cautious maximum by Lyman for fear that anything greater might be used in a weaker Italian replica Henry, 1866, 1873, or Burgess rifle.
9.0 grains of Unique (or 8.5 grains of Universal) would also be a standard pressure Colt SAA revolver load and get you to 1200 FPS or so in a 19"-20" rifle with a 250 grain lead bullet.
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From the Alliant Powder website:
250 grain Speer lead SWC (5 1/2" barrel)
- 9.5 grains Unique / 941 FPS
- 12.9 grains Blue Dot / 1028 FPS
- 15.4 grains 2400 / 972 FPS
The above would all run around 1200 FPS or more in a 20 " barrel rifle.
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More Lyman loads:
250 grain JHP/ Hornaday XTP (16" barrel)
- 9.3 grains Unique / 1102 FPS
- 9.0 grains Power Pistol / 1091 FPS
- 17.5 grains 2400 / 1236 FPS
240 grain JHP (16" barrel)
- 11.0 grains HS-6 / 1101 FPS
- 9.5 grains Unique / 1176 FPS
- 9.2 grains Power Pistol / 1127 FPS
Likewise, Lyman lists these as cautious maximums with the weak action Italian replicas in mind, but these would be easy on your Rossi IMHO. They might not be wise for extended use in the Italian weak action replicas though.
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Any of these loads would be good.
But I take no responsibility for the accuracy or results of such data (Standard Disclaimer
)
You should pickup a copy of the Lyman handbook and and maybe one which features .45 Colt rifle loads for stronger actions.