Sir.......was considering trying Accurate MagPro in my 6.5-284 norma with 140 A-max. Can I get enough of that in the case to improve upon H4831 SC? I shoot 54 gr. with no pressure signs. The only info I saw on this was for a 6.5-06 AI.

Tough question...

My testing with MagPro is limited, and my testing is even more limited with the 6.5-284 Norma.

You asked about H-4831, and mentioned your load of 54 grains. I list 50 grains as my suggested max load.

My load of 50 grains put that bullet at a tad over 2400 FPS, and I would imagine that your load of 54 grains is doing around 2600 FPS.

My next load up, 51.2 grains showed pressure signs.

My load with RL-25 (57.4 grains) was averaging around 2650 FPS, however, I found that generally accuracy was better when hanging around 2550 FPS, and that is why I chose RL-22 as my powder of choice.

Sorry I can't give you a direct answer, but I don't think a "guesstimate" is what you are looking for.

My load right now is with a 100 grain nosler BT.
I'm shooting 55 grains of IMR 4350...est vel 3300+. I saw data from Viht. for 139 lapua scenar using vvn560. for a vel of 3100 out of a 26 inch barrel. How can your vels be so slooow?

Lofter, from the Hogdon site:
http://www.hodgdon.com/data/rifle/65mm284.php
Maybe you can extrapolate form AA .270 info.
http://www.accuratepowder.com/data/PerPowder2Guide/Rifl...0235%20and%20236.pdf

My loads are "so slooow" because I measured them over a chrony, not "estimated" them by some obscure formulae.

In addition, I tested with a 24" barrel, and you are using a 26" barrel. That 2" will account for around 100 FPS, depending on load.

I doubt seriously you are getting 3300+ FPS with your 100 grain load. If I had to guess, I would say you are much closer to 3000 FPS.

As for your Lapua and VV load, I would imagine that around 61.0 grains should do that...