In the article, “Where the Road Leads – Two Gadgets That Called Out to Me.” I went on a bit about my theories regarding crimp on lead rifle loads. My thinking was that the vertical stringing I had experienced with my lead loads might have been a result of inconsistent ignition.
I bought three Lee Crimp Dies in the calibers I work with, and I took a legacy .308 lead load, randomly selected four ten round rows, and crimped 20 of the 40 rounds from that lot. Well I finally got out to the range to actually shoot them, and the results were interesting if not confusing.
The day was beautiful, but sadly I was faced with a quartering head wind that was gusting close to 25 mph. I fired ten of the uncrimped loads, ten of the crimped, ten uncrimped, and finished up with ten crimped again. The rounds were fired for group at 100 yards over a Shooting Chrony at 16′ from the muzzle. The raw results are posted below.
|High Vel||Low Vel||Avg Vel||Max Dev||Avg Dev||Std Dev|
|No Crimp||2072 fps||1981 fps||2007 fps||91 fps||18.3 fps||27.54007|
|Crimped||2096 fps||2025 fps||2066 fps||61 fps||14.2 fps||19.85391|
|No Crimp||2041 fps||1968 fps||2017 fps||73 fps||16.7||22.50062|
|Crimped||2096 fps||2042 fps||2068 fps||54 fps||10.5 fps||15.08531|
Most of the terms above are pretty much straightforward. The exception is the Standard Deviation column. The extremely non mathematic explanation is simply, by squaring the velocity deviations and playing some adding and subtracting games the resulting number does a better job of defining what the “UNIT” of deviation is amongst the string’s number of shots. The smaller that “UNIT” is the narrower the bell shaped curve of the variables is statistically. Anyway they tell me this is a better unit of comparison.
The initial impression of these rounds as I was recording the velocities was that the crimped rounds gained about 60 fps in velocity over the uncrimped ones. Remember that these were rounds selected from an already loaded lot of ammo. All loaded the sme day from the same batch of heads and all powder was dispensed from an RCBS Chargemaster Electronic scale and powder dispenser. The only difference between sequences is the crimp. Clearly the crimped rounds are getting more bang for the buck from the same powder charge. Read this as “more efficient” ignition. Read that as “more consistent.”
Subjectively, the perceived recoil of the crimped loads was more crisp. OK, at this point you’re going, “Yeah Sure!” but no, really they were!
In all possible velocity deviation measurements, the crimped loads were far more consistent. So, the logical conclusion is that “I was Right” in my theoretical deductions. OK so the WHY do the groups not confirm this?
Overall observations and conclusions are as follow:
- Remember to bring the real front rest next time! I used the prone roll as a rest.
- The gusty day may have skewed the results a bit. If we note group 4 with no sight changes drifted left.
- Fired from “rests on the bench,” these were not “benchrest” tests. While indicative, they still rely upon my ability to hold a group (read this as not so much).
- All the empirical data say to me, crimp lead reduced loads, they are statistically more consistent.
- Become a better bench supported shot!
- We’re still looking for the holy grail load!
While these loads are just fine for practice and having some fun, and definitely fall into the realm of “practically accurate,” we will have to rerun these tests another day for absolute confirmation. The occasional flyer in the above groups may have been bad castings, a bad gas check seat, or more likely a poor shot by me. Therefor this test is declared, interesting but inconclusive!