I should have looked it up before I commented, I was wrong about my light load. I'm using 210gr not 185's.

The Regulation Load:
Case: Norma
Primer: Federal 215
Powder: IMR 4831 82grs
Bullet: Woodliegh 400gr Soft
2050FPS

The Bullets for the other loads are:
Hornady 41Cal(.410) 210gr XTP's
and
Hornady Interlock 405 Caliber(.411) 300gr Flat Nose

Below is the load data I was provided with the rifle:
Caliber: .450-400 NE 3” (400 Jeffery)
Barrel length: 24 to 26”
Powder: Accurate -- 5744.

Bullet weight: 210 grains.
Reduced load: 37.0 grains (1650 – 1750 ft/p/sec)
Midrange load: 47.0 grains (2200 – 2300 ft/p/sec)
Maximum load: 60.0 grains (2750 – 2850 Ft/p/sec)

Bullet weight: 300 grains.
Reduced load: 36.0 grains (1650 – 1750 ft/p/sec)
Midrange load: 50.0 grains (2175 – 2275 ft/p/sec)
Maximum load: 55.0 grains (2275 – 2375 Ft/p/sec).

Bullet weight: 350 grains.
Reduced load: 33.0 grains (1550 – 1650 ft/p/sec)
Midrange load: 44.0 grains (1850 – 1950 ft/p/sec)
Maximum load: 52.0 grains (2100 – 2200 Ft/p/sec).

Bullet weight: 400 grains.
Reduced load: 30.0 grains (1400 – 1500 ft/p/sec)
Midrange load: 40.0 grains (1700 – 1800 ft/p/sec)
Maximum load: 49.0 grains (1900 – 2000 Ft/p/sec).

Edited to add:
I'm using a felt fiber filler. Just enough to seat the bullet with a very light compression.

I haven't tried anything in the 350gr range, I figure with the 210, the 300 and the 400 I am pretty well covered.

Hope this helps,

Colin