Lane used the V/C ratio method and Ruger Model 77 Hawkeye rifles to develop handloads for the .300 RCM and .338 RCM when no published data existed.

In last October's issue, I described an empirical method one could use when working up a new handload. Apparently I didn't do a good job explaining how to apply it because I received several inquiries from interested but puzzled readers. Let me make amends by emphasizing the key aspects of this handy scheme: 1.) You must chronograph your handload's average velocity. 2.) You calculate the V/C ratio by dividing the average velocity of a batch of test loads (at least 10 rounds) by the propellant charge weight. For example, .30-06 cartridges charged with 57.3 grains of Reloder 19 should deliver approximately 2,700 fps in a rifle with a 24-inch barrel (according to Sierra's 5th edition reloading manual). The V/C ratio is 2700 ÷ 57.3 = 47.1. 3.) Dynamic V/C ratio is the increase in velocity resulting from each grain the propellant charge is increased. For example, if you step up the powder charge by 1/2 grain and the average velocity increases 32 fps, then the dynamic V/C is calculated as 32 ÷ 0.5 = 64. 4.) As you work up your hand-load, you should compare the dynamic and average V/C values for each increase in charge weight.

Using the values from 2.) and 3.) above, the ratio of the dynamic to average V/C is 64/47.1, or 1.36. If the dynamic value exceeds 1.5 times the average V/C ratio, you must repeat the specific test load to verify the value. If so, the data suggests your handload is surely approaching the maximum limit, so you may choose to proceed cautiously if there are no other indications of excessive pressure. 5.) If the average V/C ratio is lower than the value calculated using published load data, your handload/rifle system is less efficient than the one used to develop the load manual's data, so you may have to exceed the recommended maximum charge weight to achieve the corresponding maximum velocity. Do so carefully in small steps while watching for obvious pressure signs. Conversely, if your loads exhibit a greater V/C value than the published data, your system is apparently more efficient, and you may reach the maximum velocity listed using less than the corresponding maximum charge weight shown in the manual. Never try to exceed the maximum velocity. The laws of physics regarding energy conversion are quite rigid. If your bullets chronograph even 50 to 100 fps faster, then you're surely exceeding maximum safe working pressure.

Typically, for many reasons, a handloader gets an itch to develop a load for a favorite rifle using a new propellant he hasn't tried before. I started out loading for my .270 Winchester with Hodgdon's surplus 4831. At only a dollar a pound, I didn't mind the dealer scooping it out of a 50-pound keg and pouring it into a small paper sack. Later, I discovered IMR-4350 might be a suitable option. It was twice the price of 4831 but came in a sturdy can that stored on the bench better, plus I thought it might launch the bullets faster and maybe even straighter. I checked out DuPont's load-data sheets and made up some test loads. An electrical-technician friend had recently designed and fabricated a homemade chronograph for me. It was crude and cumbersome to use, but it measured bullet velocities, and as an engineer, I could always use more data.

Looking back at my records and comparing them to the old DuPont recipes, the average V/C for my Winchester Model 70 was 52, whereas the V/C for the DuPont data was 54. As the powder charge increased, the average V/C remained almost constant, and the dynamic value was stable, i.e., increasing essentially linearly without abrupt change. However, according to the V/C theory, because the ratio for my handloads was lower than the DuPont V/C ratio, my handload/rifle system was somewhat less efficient.