Kamilaroi-

Careful with this.
Look through my posting history here, I've asked this question before and have gotten different answers.
Having tried numerous powders, bullets, and loads I finally found a load that works right in my rifle.
I was very cautious working up to a regulation load.
Don't try my load in your rifle without serious consideration, comparison, examination of your rifle, and from having worked your way to anything near it from waaaay below the standard "start ten percent low and work your way up..."
My Tolley takes a wicked big charge of powder to do it's thing. This isn't the only feature of the rifle that's unusual.

I haven't seen another BPE rifle take this much powder to shoot this velocity with this bullet weight.
My rifle weighs 10-1/4 lbs and runs at 2025fps
Marrakai's rifle regulates at a lower velocity, takes less powder to do it, and it weighs 1-3/4lbs less.

In Birmingham, Wright ran the 500/450 3-1/4" Nitro For Black:
Bertram 3-1/4" 500/450 brass
70.0gr Varget
350gr SNRN bullet
2020fps
9.0tpsi

Compare that to his note that the period mean service pressure for the black powder load was 11tpsi.

The 500/450 3-1/4" Magnum BPE took 140gr powder
My Tolley (and Marrakai's) call for 150gr powder
The ten grain difference takes that extra 1/4" of case to handle it. The increase in chamber volume will affect the pressure readings (compared to Wright's results)

The load for my rifle
Bertram 450no2NE 3-1/2" brass
Fed215 primer
76gr Varget
21gr Dacron (frim to the bullet)
Hornady model#4502 350gr SNRN jacketed bullet
2025fps (10ft from the muzzle)

Careful with that!

What exactly is your rifle?
What's it chambered for?
Is it a bottleneck (500/450) case?

Cheers

--Tinker