Diminishing returns of powder vs. velocity

[texasmac]

The following should be interesting to you Browning .40-65 BPCR owners. I’m working on an article on the BACO JIM410410M1 bullet (408.7gr using 16:1 alloy) in the Browning with Swiss 1.5Fg & needed some velocity data vs. powder capacity. I thought I’d share the data. I did not shoot for accuracy, only over a chronograph to determine average velocities for each load. 5 shots were fired with each load and I wiped between shots. A chart with the data is below. BTW, it’s always been my rule-of-thumb not to compress Swiss 1.5Fg more than 0.1” for best accuracy, which is not confirmed or unproven by the chart

Since the chronograph provided standard deviation data, I included it even though it should not be taken as an absolute indication of accuracy due to other factors also affecting accuracy. Although, with that said, the two lower SD values in the chart do coincide with the best two accuracy loads for my rifle with the 410410M1 bullet.

Another observation: if you do the math you’ll note that the changes in compression are about 0.026” per grain. This is due to the Browning chamber having a constant diameter 0.5” long neck resulting in each additional grain of powder being compressed the same amount. In chambers such as the Shiloh .40-65, the neck has a constant taper resulting in more compression required for each additional grain of powder assuming the bullet seating depth does not change.

Wayne

[boommer]

Wayne who's cases are you using ? the rifle I got off of you I use 65 gr volume 2f swiss .60 card,construction paper between card paper and bullet 250 thousand compression and 409 420 M4 BACO,so it ends the bullet kissing the rifling. I use Winchester cases.

[texasmac]

Wayne who's cases are you using ? the rifle I got off of you I use 65 gr volume 2f swiss .60 card,construction paper between card paper and bullet 250 thousand compression and 409 420 M4 BACO,so it ends the bullet kissing the rifling. I use Winchester cases.

Hi Clayton,

The cased are Remington refomed from .45-70.

Wayne

[Good Cheer]

Graph paper charting of powder volume versus velocities gives interesting data for when you ponder the S curve on the paper and what it's telling you about your piece. But that's more so with front stuffers than brass cartridge guns.