|April 10, 2013, 03:56 PM||#1|
Join Date: October 18, 2006
8x57 match ammo, Quickload sort of problem
Background: I'm putting together a K98 sniper for NRA vintage sniper rifle matches and am trying to duplicate a service round (196gr FMJBT at 2500 fps) using a 200 gr Matchking bullet.
Reviewing Hodgdon's data for 200gr bullets I see four powders with similar burn rates having weird inconsistencies between brands. Basically anything made by ADI in Australia (Hodgdon's Extreme line) has over 100fps advantage at max charge over anything made by GD in Canada (IMR).
The four powders are IMR 4895, H4895, Varget, and IMR 4064. In 308 Win these powders are all within pretty close double digits of each other pushing a 190gr bullet, which is what I expect for powders of such similar composition, energy density, and burn rates.
In 8x57, pushing a 200gr bullet, that relationship breaks down.
For example Varget and 4064. Starting charges are within a half grain of each other, but max charge is three grains higher for Varget (and only 800 CUP more pressure?)
200 GR. SPR SP IMR IMR 4895 .323" 2.970" 39.0 2112 34,900 CUP 45.0 2409 48,500 CUP
200 GR. SPR SP Hodgdon H4895 .323" 2.970" 38.0 2240 36,800 CUP 45.4 2539 49,200 CUP
200 GR. SPR SP Hodgdon Varget .323" 2.970" 40.5 2183 36,900 CUP 47.5 2511 49,100 CUP (Dividing pressure by max charge gives 1033 CUP per grain.)
200 GR. SPR SP IMR IMR 4064 .323" 2.970" 40.0 2193 36,200 CUP 44.5 2401 48,300 CUP (Dividing pressure by max charge gives 1085 CUP per grain.)
So it seems to me that you could get the same pressure as Varget by using another 0.7 grains of IMR 4064. That data would bring the max charges to 2.3 grains apart.
Now, I know that pressure increases is NOT a linear function, but for the sake of not having the curves in front of me I will assume linearity for small charge increases.
I see a few possible reasons for this disparity, but I don't have enough data/knowledge to know what is really going on.
Option 1: The Aussie powders really are that much better than IMR's equivalent lineup.
Option 2: The IMR data is lawyered down for the American market (or a holdover from the old Dupont days) and the data for the Aussie powders is republished from ADI (or more recently generated).
Option 3: There is a combination of 1 and 2 at work.
Option 4: The data is valid for each powder, but the data was gained on different equipment (for example a copper slug method for IMR and a piezo sensor for ADI).
So, anyone with quickload willing to play around and see if there is any insite to be had by this apparant inconsistency?
"Gorsh" said Goofy as secondary explosions racked the beaten zone, "Did I do that?"