The Hunter doesnt exactly have a canon in-game height but he does have a 1/6 scale model that just so happens to come with a 1/6 scale model of the Kirkhammer, so we'll use that as a frame of reference:
320 mm / 800 = 0.4 mm/px
0.4 x 723 = 289.2 mm
289.2 x 6 = 1735.2 mm, 1.7352 m
That's The Hunter's height
Now for the Kirkhammer:
0.4 x 252 = 100.8 mm
100.8 x 6 = 604.8 mm, .6048 m (Hammer length)
.6048 / 691 = .00087525325 m/px
.00087525325 x 532 = .465634729 m (Hammer height)
.00087525325 x 235 = .20568451375 m (Hammer width)
.00087525325 x 251 = .21968856729 m (Gap height)
.00087525325 x 94 = .08227380607 m (Gap width)
.6048 / 237 = .00255189873 m/px
.00255189873 x 83 = .21180759493 m (Gap length)
Volume = l*w*h = .6048 x .465634729 x .20568451375 = .057924 m^3
Volume = l*w*h = .21968856729 x .08227380607 x .21180759493 = .00382834064 m^3
.057924 - .00382834064 = .05409565936 m^3
Density of granite = 2700 kg/m^3
2700 x .05409565936 = 146.058280272 kg (Mass of the Kirkhammer's head)
Now that we have that, we can get force from the swing of the hammer. Going to be borrowing some math from here with some updated numbers:
.6048 / 237 = .00255189873 m/px
.00255189873 x 301 = .76812151773 m (Hand to center of mass)
.00255189873 x 135 = .34450632855 m (Hand to elbow)
.00255189873 x 114 = .29091645522 m (Elbow to shoulder)
.76812151773 + .34450632855 + .29091645522 = 1.4035443015 m (Swing radius)
Circumference = 2πr = 2π(1.4035443015) = 8.81873 m
We're still going to be using the Transformed R1 and Transformed L2 attacks. Bloodborne runs at 30 fps, so:
Half rotation swing = 7 frames = 0.2333333333333333341 seconds
Full rotation swing = 10 frames = 0.3333333333333333 seconds
Half rotation swing speed = 4.409365 / 0.2333333333333333341 = 18.8972785714 m/s
Full rotation swing speed = 8.81873 / 0.3333333333333333 = 26.45619 m/s
Half swing force = 37162 Newtons, 3.7895 Ton of force, Class 5
Full swing force = 72837 Newtons, 7.4273 Ton of force, Class 10