Hi I have some questions about H322 and Benchmark:

Is it position sensitive?
Is it temperature sensitive?
Is it suitable for reduced loads?
What fill rate does it need to function correctly?
Does it pressure spike?
What pressure range will it operate well in?

If anyone can answer any of the above questions. Please do.

What cartridge?

6.5x55 139 grain cast bullet 1800-1900fps is what I am aiming for, but its only a 45% fill. I have taken H4895 down to 41% and H4198 to 33% which are either side in burn rate.

Some powders are weird is H322 one of them?

The powder you want is H4895/2206H, it can be reduced to 60% of normal loads without pressure spikes.
I haven't reduced either powder you mention, but have used Benchmark extensively in 17, 222 and 22-250/AI. It's a very stable powder and may work just fine for what you want to do, but generally faster powders work better for this. I believe H322 is a ball powder similar in burning rate to 748, I don't believe this powder would take to reduced loads well. Use with caution.
The Lee handloading book has extensive data for reduced loads, but unfortunately it lists powders not generally available in Australia, I will look it up and get back to you.
Edit to add:
Looked up the reduced load, it appears that H4895 is ideal for what you're wanting. A 40% reduction is about right, it appears Benchmark may not be suitable for reducing as much as you want.

Cheers.

This does not directly answer any of your questions, but I can't say that benchmark is one of the cleanest burning powders I have used in my gas operated semiautomatic rifles. It is for this reason, in addition to its accuracy in the 223 Remington, that I highly recommend it.

H322 is a fine extruded powder - not a ball powder. It provides excellent accuracy - meters very accurately. It is not one of the "extreme" powders designed to be temperature insensitive. Burn rate is similar to H4198, and in between Vihtavouri N120 & N130. Faster burning than Benchmark. Typical pressure range is 35,000 to 50,000 CUP, of course depending on the cartridge. It shines for the smaller benchrest rounds, the 6.8 SPC, 45-70, etc. Recommend that you go online to Hodgdon's website for loading data. It probably is better for lite loads than 4895. I don't have any specific data on that.

Both H322 and Benchmark are "extreme powders".

ADI Benchmark 2 is the same powder as Hodgdon Benchmark.
I second the use of H4895/2206H in reduced loads. Benchmark and H322 work great in my 223 and 6x45 but that is as far as I've done much with them. You might look at Trail Boss too.

quote:

Originally posted by PRW:
H322 is a fine extruded powder - not a ball powder. It provides excellent accuracy - meters very accurately. It is not one of the "extreme" powders designed to be temperature insensitive.

Both my 1# can and my 8# jug of H322 have the "extreme" logo on the label

I have not tried either in reduced loading but; I do use AA 2015 in reduced loadings and it works great. Both Benchmark and H 322 are in that burning range, both small kernel extruded powders, both light easily, so should be workable. I have used the AA 2015 in reduced loadings in the .458 Win Mag, 30-06 and the 35 Whelen, and it works well.
Your powder choices should be workable at 20-25 grains, working your way up and letting the target tell you when it is good. All other pressure, warning signs etc. of course, Chronograph is great, somewhere between 1400 and 2000 fps is all you need.

H322 is my powder of choice for a low recoil 45-70 load. 25 grains of H322 will about half fill the case. When I seat a 405 grain cast lead bullet over it. It shoots to point of aim at 100 yards with very little recoil.

I tried H322 in my Mannlicher Scoenauer 9.5X57MS and 250gr Sierra bullets for around 2200 fps. Definitely less recoil and barrel flip. With open sights it does not shoot as high as other powders (which also had lower velocity in some cases).

you will answer all your questions by shooting your loads, and when you get your best accuracy without pressure warning, you have done good! So many overthink gun stuff!