I’ve been doing load development on my .300 PRC over the past three to four months. In the end I arrived at a load that works fairly well, but only after going a bit old-school and shooting ladders all the way up to Hodgdon’s published maximums.
I’m currently shooting the Hornady 225gr ELD-M out to 1 km, but I’m keen to also try the Bergers (230gr, 220gr, and 215gr - most likely the 230 if everything else is equal). I’m also tempted to develop a load for the Barnes 208gr LRX. Although this is not primarily a hunting rifle, the more I shoot it the more I find myself tempted to setup on a hill and wait for a kudu to appear somewhere at distance.
I’ve used both QuickLOAD and GRT quite a bit for my .375 H&H, and in that cartridge they have been reasonably accurate. On the .300 PRC, however, I’ve found the predicted velocities with H1000 and Retumbo to be quite far off from what I’m actually seeing on the Labradar / Garmin. Before I just ask for advice on specific powders and starting loads for the Berger and Barnes bullets, I’d like to ask for help to understand why QuickLOAD is so far out in this case.
I’m running QuickLOAD 3.9 with the latest database update purchased in December.
Here’s the rifle and case data:
Rifle: Howa .300 PRC
Barrel: 26"
Suppressor: Yes
Twist: 1:8.5
Brass: Lapua
Trimmed length: 65.18 mm
Case capacity: 97.0 gr H2O (average of five fire-formed cases)
Current load:
Bullet: Hornady 225gr ELDM
COAL: 93.5mm
Jump: 1.3mm
Propellant: 78.7gr Retumbo
Primer: Federal 215M
Speed: 2863fps (Measured with the Garmin across 42 shots. Labradar LX said 2837fps, but I only used it for 4 shots and it measured my 78.5gr at 2839fps also across 4 shots - so I think the 2837 is too low).
SD: 10fps across 42 shots when using the Garmin.
When I enter this data into QuickLOAD, it predicts a muzzle velocity of 2683 fps for this load, which is about 180 fps lower than what I’m actually seeing. On my .375 H&H, QuickLOAD’s predictions have always been much closer to reality than this, so this difference worries me a bit.
My first question is whether it is reasonable to apply such a large powder burn-rate or energy calibration to Retumbo in QuickLOAD to make it line up with measured velocity? My follow-up question is whether, after doing that, it is still sensible to use the calibrated model to look for nodes and develop loads for other bullets when using Retumbo?
And then as a third question to sneak in here
I did a test with CCI 250 primers and measured across 4 shots it seems like I'm losing around 50fps. I know the Federal primers are said to be "warmer", but most people I asked said that I wouldn't really see a difference between the two. So I am wondering what the experts here say about Federal vs CCI for this cartridge?PS I am no longer shooting the H1000 because I ran out during load development and couldn't find more of it at the time. But I saw similar big discrepancies between what QuickLOAD (and GRT) predicted vs reality.
