Hi Ian,

I bought one of the first maufactured Heym Express rifles in 500 A-Square (24" barrel).

Case forming:
basic case: Norma 460 Weatherby, shoulder and neck annealed
Primer: Large PISTOL
Powder: 5-8grs Bullseye
Put a small piece of tissue on top of the powder charge, the fill the case to the shoulder with cream of wheat.
On firing the cartridge (only at the shooting range) the shoulder/neck area was formed perfectly
(This case forming procedure was described in Donelly´s book of Cartrige Conversion)
Formed cases are too short, but can be used.

It should be no problem to use this method also in the 378 Wby case, but I recommend to decrease the powder charge.

Powders:
I used fast to medium burning powders:
Kemira N135 and N140
IMR4895
Dynamit Nobel R902 (equivalent to Reloader 15 ?)

Bullets:
all bullets for 500 Jeffery and 500 NE work fine, if you reduce loads to the intended velocity range of the bullet. I only use soft point bullets fore range practise. The once available 700grs RN Soft Point from Barnes gave not enough velocity and was too expensive for further testing.

The slower powders gave not enough velocity, but are good for reduced loads(=fill the case):
Case: 460 Wby Norma reformed;
Primer: Federal 215 LR Mag.;
Bullet: Woodleigh 570grs Soft Point RN
Powder: IMR 4350 100.0grs
V5: 565m/s - 1850fps
energy: 5900J - 4350 fpe

practise load/ conservative hunting load:
Case: 460 Wby Norma reformed;
Primer: Federal 215 LR Mag.;
Bullet: Woodleigh 570grs Soft Point RN
Powder: Kemira N140 112.0grs
V5: 720m/s - 2360fps
energy: 9600J - 7070 fpe
This load can be increased in my rifle to 117.0grs, but I would´t use this load for hot weather and some kind of optimism is required to touch off this round, at least for me...

Equivalent to 500 Jeffery:
Case: 460 Wby Norma reformed;
Primer: Federal 215 LR Mag.;
Bullet: Woodleigh 535grs Soft Point RN
Powder: Dynamit Nobel R902 100.0grs
(veloctity numbers not available)

If you need more inforamtion, then please send me a PM.

best regards
Rolf