entoptics
Well-Known Member
- Joined
- Jan 16, 2018
- Messages
- 865
Having some ES/SD issues with a 7mm Rem Mag, so I decided to run an experiment to see if brass weight could be the problem. I knew it was unlikely, but figured I should eliminate any possible variables (and COVID = what do I have better to do?). The results, though not perfectly well behaved, surprised me at least a little.
Summary for those who don't like nerd details...~1-3 fps per grain of brass. Weight sorting brass almost certainly can make a measurable difference, though it's highly unlikely to be the source of large ES/SD problems on average. I'd place brass weight pretty low on my list of "ways to improve ES/SD".
Nerd Details...
Brass Prep (not necessarily in this order, but close enough)
Remington brass, 2X fired, some not in this rifle, though all required FL sizing and shoulders bumped back.
SS Pin tumbled after universal decapping die.
Necks skim turned to ± 0.0005"
Salt Bath Annealed
RCBS Competition FL sized, no expander button, shoulder bumped to 0.002" ± 0.001"
0.283 Sinclair neck expander mandrel.
Trimmed to ± 0.001", chamfered, deburred
Flash holes chamfered
Primer pockets scrubbed (not really uniformed, though a little brass gets removed from the bottom making them a touch flatter)
Sorted by weight (± 0.1 gr)
Load
66.07 gr of H1000, weighed to less than a kernel (ES of 0.02 gr, SD of 0.007 gr)
180 gr ELD-M
Fed 215M primers
~0.02" off lands (± 0.001 BTO)
Powdered graphite applied to neck ID with q-tip after powder charged
4 shots each at 4 different brass weight "groups". ~227.5 gr, ~ 229 gr, ~230 gr, and ~233 gr. The lower and upper groups had wider spread, as I didn't have enough brass at the ends of bell curve to keep them tightly grouped.
Methodology
All shots were fired from prone, front rest, rear bag.
LabRadar acquired data for 80-150 yds for all shots, and raw data was checked in my regression spreadsheet to ensure no spurious readings.
Shots were fired "snake style" in 4 shot groups, with the rifle cooling for at least 10 minutes between each string to mitigate heating and fouling bias. i.e. Weight 1, W2, W3, W4, cool. W4, W3, W2, W1, cool, W1, W2, W3, W4, cool, W4, W3, W2, W1.
The rifle barrel was never more than "lukewarm to the touch".
No rounds were allowed to "stew" in the chamber, all were fired within ~10 seconds of closing the bolt.
Results
Disclaimer: I lost one velocity due to LabRadar failure, and one bullet blew up in flight (recurring problem for another thread). Though I got a velocity, it should be considered suspect. Due to the limited number of shots, the statistics are weak, but on the whole, I believe the conclusions are valid.
Brass weight vs Velocity
4 shot average of different weights vs velocity (3 shot for ~229 gr group).
Summary
Though I'm having ES fliers (2850 and 2929 in particular), which are certainly biasing the data, with 16 shots total, I think the results are robust enough to conclude that brass weight, and by extension internal volume, affects velocity.
That being said, I suspect it's almost completely negligible unless you have VERY extreme weight variations, or are shooting at such extreme ranges that you need single digit ES values. For perspective a single kernel of H1000 (~0.025 gr) is worth about 1 fps if you calculate velocity vs charge weight (e.g. 2900 fps / 66 gr = 43 fps/gr. 43 fps/gr x 0.025 gr = 1.1 fps)
This test spanned ~6 grains of brass weight variation in ~230 grains (±1.5%). If you cherry pick the worst case scenario, it only amounts to ~4 fps per grain of brass weight. If you cherry pick the best case scenario, it might be as low as 1 fps per grain of brass weight.
Hope you find this interesting.
Now I need to inspect the two extreme flier brass to see if I can figure out what's ACTUALLY causing my poor ES/SD issues in this particular rifle. All my other rifles/loads run less than 20/10 ES/SD without much effort. Something is wrong somewhere...
Summary for those who don't like nerd details...~1-3 fps per grain of brass. Weight sorting brass almost certainly can make a measurable difference, though it's highly unlikely to be the source of large ES/SD problems on average. I'd place brass weight pretty low on my list of "ways to improve ES/SD".
Nerd Details...
Brass Prep (not necessarily in this order, but close enough)
Remington brass, 2X fired, some not in this rifle, though all required FL sizing and shoulders bumped back.
SS Pin tumbled after universal decapping die.
Necks skim turned to ± 0.0005"
Salt Bath Annealed
RCBS Competition FL sized, no expander button, shoulder bumped to 0.002" ± 0.001"
0.283 Sinclair neck expander mandrel.
Trimmed to ± 0.001", chamfered, deburred
Flash holes chamfered
Primer pockets scrubbed (not really uniformed, though a little brass gets removed from the bottom making them a touch flatter)
Sorted by weight (± 0.1 gr)
Load
66.07 gr of H1000, weighed to less than a kernel (ES of 0.02 gr, SD of 0.007 gr)
180 gr ELD-M
Fed 215M primers
~0.02" off lands (± 0.001 BTO)
Powdered graphite applied to neck ID with q-tip after powder charged
4 shots each at 4 different brass weight "groups". ~227.5 gr, ~ 229 gr, ~230 gr, and ~233 gr. The lower and upper groups had wider spread, as I didn't have enough brass at the ends of bell curve to keep them tightly grouped.
Methodology
All shots were fired from prone, front rest, rear bag.
LabRadar acquired data for 80-150 yds for all shots, and raw data was checked in my regression spreadsheet to ensure no spurious readings.
Shots were fired "snake style" in 4 shot groups, with the rifle cooling for at least 10 minutes between each string to mitigate heating and fouling bias. i.e. Weight 1, W2, W3, W4, cool. W4, W3, W2, W1, cool, W1, W2, W3, W4, cool, W4, W3, W2, W1.
The rifle barrel was never more than "lukewarm to the touch".
No rounds were allowed to "stew" in the chamber, all were fired within ~10 seconds of closing the bolt.
Results
Disclaimer: I lost one velocity due to LabRadar failure, and one bullet blew up in flight (recurring problem for another thread). Though I got a velocity, it should be considered suspect. Due to the limited number of shots, the statistics are weak, but on the whole, I believe the conclusions are valid.
Brass weight vs Velocity
4 shot average of different weights vs velocity (3 shot for ~229 gr group).
Summary
Though I'm having ES fliers (2850 and 2929 in particular), which are certainly biasing the data, with 16 shots total, I think the results are robust enough to conclude that brass weight, and by extension internal volume, affects velocity.
That being said, I suspect it's almost completely negligible unless you have VERY extreme weight variations, or are shooting at such extreme ranges that you need single digit ES values. For perspective a single kernel of H1000 (~0.025 gr) is worth about 1 fps if you calculate velocity vs charge weight (e.g. 2900 fps / 66 gr = 43 fps/gr. 43 fps/gr x 0.025 gr = 1.1 fps)
This test spanned ~6 grains of brass weight variation in ~230 grains (±1.5%). If you cherry pick the worst case scenario, it only amounts to ~4 fps per grain of brass weight. If you cherry pick the best case scenario, it might be as low as 1 fps per grain of brass weight.
Hope you find this interesting.
Now I need to inspect the two extreme flier brass to see if I can figure out what's ACTUALLY causing my poor ES/SD issues in this particular rifle. All my other rifles/loads run less than 20/10 ES/SD without much effort. Something is wrong somewhere...