December 30, 2021
One of my gunsmith’s hunting buddies, Rusty, called the other day asking for some specific reloading advice. He asserted that he’d had enough of cleaning guns to last the rest of his life and intended to only load “one of those new copper-cleaning propellants.” Unfortunately, his two favorite hunting rifles are chambered for cartridges for which there isn’t any load data using those new-type powders.
Rusty told me he has always used IMR 4064 for his two favorite cartridges (.35 Remington and .35 Whelen), and he thought IMR 4166 Enduron looked like it would be suitable. So I called one of my sources at Hodgdon, which owns IMR, and asked about it. My source said it would work and to start out by reducing the maximum loads for IMR 4064 by 5 percent.
When I relayed that info to Rusty, he said he’d do that and then work up incrementally as pressure signs allowed. I told him to go out and get a chronograph.
Trying to read pressures by measuring case head expansion or judging how flat the primer looks is about as useful as someone predicting your future by reading your palm or peering into a crystal ball.
I was in college when I first encountered the following tenet: Without reliable data, you can’t readily assess and control any situation. Since Rusty wants to pursue an uncharted course with his handloads using a propellant for which there is no applicable data, he must measure his test loads’ velocities to achieve safe and reliable results.
Bullets are launched from the barrel by the pressure generated when the primer and powder charge are ignited and consumed. Increasing velocity is the direct result of greater pressures. The universal adage of “you don’t get something for nothing” is definitely applicable when addressing velocity. Even if you don’t know your load’s velocities are exceeding the expected maximum levels, the actual pressures are almost certainly unsafe.
For 30 years, I’ve measured velocities with a chronograph. Using common sense and conservative deductive reasoning, I compared my experimental results with velocity data in the latest reference load manuals.
According to Hodgdon’s burn rate chart, IMR 4166 is typically a bit faster than IMR 4064. Let’s say Rusty backs off his favorite IMR 4064 max charge weights by 5 percent, loads and fires five test loads, measures velocities, and compares the results with Hodgdon’s IMR 4064 velocity data. If the average velocity is 200 fps slower but forms a half-inch group at 100 yards, he might decide that’s good enough.
If he chose to experiment further, he’d bump up the powder charge in half-grain increments and load five rounds each of four or five additional sets of test loads. At the range, he’d fire the first batch and record velocities. Assuming he hasn’t yet attained the IMR 4064 max velocity, he’d fire the next batch and record the results. He would not try to exceed the velocity corresponding to the max IMR 4064 recipe for the same bullet weight and type.
Now he has two or more sets of velocity data. His favorite IMR 4064 load’s average velocity is sort of like the target, assuming nothing untoward occurs during the incremental load tests. He can compare the delta velocities from test load one to two and two to three, etc. If they’re linear and gradually declining, my experience suggests everything is still safe.
However, if the delta velocity between steps is increasing but erratically, or the standard deviation is greater than 20, the pressures are not increasing consistently, i.e., they’re not predictable. And if two consecutive test loads’ average velocities are quite close, he’s likely reached the practical max pressure limit. He might try a different primer or vary the bulletseating depth to achieve more consistent velocity data or improve accuracy.
Without any velocity data, Rusty will be almost completely in the dark. He’s back to assessing flat primers, sensing the felt recoil, gauging bolt lift stickiness, etc. He has no technically reliable measurements to assess how safe his handloads are.
Coincidentally, while I was preparing this column, I drove to my club’s shooting range to test IMR 7977 and IMR 8133 Enduron propellants in a cartridge for which there wasn’t any published data for those powders. I already had velocity results for H1000 topped with the same bullet.
I had previously discussed the relative differences between IMR 7977 versus H1000 and IMR 8133 versus Retumbo with Hodgdon technicians, and I was confident my charge weights were conservative. When I fired my test loads, there were no surprises: bolt lift was normal, primers looked good with no cratering, etc., and every bullet punched a hole in the target. One load looked promising.
My conversation with Rusty ended with mixed conclusions. He acknowledged he needed a chronograph, but he also lamented the current component situation. He could readily acquire or borrow a chronograph, but it might be quite a while before he could find any IMR 4166 propellant.