Dissertation on Building Practice Hand-loaded Rounds for Muzzle Energy
Introduction:
There are posts on this forum often asking for recommendation for self defense and practice rounds in a given handgun. I chose a self defense round and worked to build practice rounds that provide the same felt recoil as the defense rounds. This way I could practice with what I shoot performance wise. And, save money as my self defense rounds are $23.00 for a box of twenty. I can build my own rounds for far less. The problem I had to mitigate was using 158 grain rounds, which I have in plenty, and the 135 grain rounds of the defense rounds. The test revolver is a S&W 640-3. I needed to find a charge that yielded a Muzzle Energy (Me) with a 158 gn RN as the Gold Dots do with a 135 gn bullet.
The Math
• Muzzle energy is calculated by the formula E=MV2/450400 for the imperial system.
• M is bullet mass in grains or grams (depending on the UOM, 0 < M < 2000.00 grains or 130 grama)
• V is the bullet velocity in ft/sec ( 0 < V < 5000.00 fp/sec or 1500 m/sec)
• The constant 450400 comes from 7000 (grains in a pound) multiplied by (g=32.17) by 2.
• 2000 comes from 1000 (grams in kg ) multiplied by 2
(note: equations and related data above download from the internet - I did not record the source URL)
* I used the data from Speer God Dots with this formula and verified the equation.
This article will address finding your own practice rounds that give similar results as your defense rounds. There is some math involved not beyond basic algebra and the use of a spreadsheet such as Excel. Knowledge of statistical analysis will make the process easier but not required beyond standard Mean, Standard Deviation, and middle functions in Excel. The muzzle energy formula is solved of velocity (as bullet mass and energy are fixed) and set into the spread sheet for easy work.
Any work such as this must be controlled. Testing needs to be designed for control to ensure the outcome is repeatable. Any and all variations must be controlled and accounted for valid experimentation else your wasting your time and resource.
Test Equipment Set-up
A Chronograph is necessary. I use a Chrony Beta. I also use an old camera tripod to mound the chronograph on. I sometimes use a folding table and bench to support a bench rest and to sit at. This can be time consuming and I like to be comfortable when I can. I use a 100 foot tape measure to set the chronograph 15ft from the table edge, and my target at 25 yards (if I am shooting at a target for grouping also). I control this set-up each time I do gather data to insure exacting and controlled test parameters. I load at least ten (10) rounds to test as this is a good sample size.
Building the test rounds
I guess I am anal somewhat. As mentioned before, everything is controlled. I used Winchester 38sp cases. I used the same cases from start to finish. All cases are tumble in a Lyman tumbler over night. Initial case preparation required all cases to be trimmed to the same length. I trimmed the cases to 1.149 inches. This value was chosen from the 48th Lyman Reloading Manual as the length they used. I use a Hornady Trimmer. I found this unit gives repeatable results without constant measuring of the cases and adjusting the trimmer. The primer pockets are clean after de-capping each time.
The charges are trickled using a Lyman trickler into a Hornady Balance Scale. (I do not like digital scales for this work – it is because of the hysteresis of the readouts). The scale sits on a leveled granite stone and is check at “zero” and calibrated at the charge weight. There is no tolerance in charge weight – the scale either balances or it does not. The charge is adjusted until the scale balances each time.
The bullets are seated to the same depth and verified with a (recently) calibrated dial caliper. (I use a dial caliper for the same reason I use a balance scale. As with the charge there is no tolerance. If the bullet is not seated deep enough, the press and die are adjusted until it is correctly seated. If it is seated too deep, the round is taken apart and redone. I use RCBS dies and a Lee single stage press. I finish up with a Lee Factory Crimp die and verify my over-all length, else it gets redone. Needless to say;
I control what I can, mitigate to minimize the effects of what I cannot control and I have found I have repeatable results.
The Test Results
Below is a table constructed of the data collected from each outing.
3.5gn 4.1gn 4.6gn 4.7gn
620.40 648.70 756.50 861.60
581.90 662.80 795.00 810.50
592.40 729.60 837.00 865.20
529.00 677.50 826.20 808.50
638.70 671.40 781.80 855.80
559.10 691.00 786.20 831.00
543.50 701.10 846.60 844.90
500.40 701.10 780.80
516.20 855.40
Mean 564.62 685.40 804.19 832.29
StDev46.67 25.62 33.02 30.11
Range138.30 80.90 90.10 84.40
Median570.50 684.25 795.00 837.95
Mv 588 691 808 836
Discussion of the data
You will note that there are less than 10 samples in two of the test – these are the result of issues with the chronograph not reset – a malfunction between user and the machine at the brain. I use a program called “PointBlank” to find the muzzle velocity – I adjusted the program in velocity until the velocity at my test distant equaled the same in the program. This is that difference. The spread sheet makes it easy to find the mean and other stuff to consider. I started with only the first two (2) samples at 3.5 and 4.1. This data was inputted into a spread sheet for linear regression analysis (don’t ask!!!) From the results of that analysis I figured I need a charge of 4.63 grains to yield the results I want. Therefore I build rounds at 4.6 grains and 4.7 grains respectively.
The next two (2) columns reflect the test results of those rounds. A table of the results for Mv and Me follows;
Charge 3.5 4.1 4.6 4.7
Mv 588 691 808 836
Me 121 167 229 245
My goal of a round with 222 ft-lbs of Me is realized with 4.6 gains of charge. It is close enough for me. I am happy!!! I have a practice round that emulates a Gold Dot round at a much lower cost. It just took patience and time to find it.
A spreadsheet chart of the four tests is included.
I had fun and will repeat this process for a 45acp - I hope this helps clear some concern on how to build rounds.
Regards,
Rick
Dissertation on Building Practice Hand-loaded Rounds for Muzzle Energy
Linear Mode
