Friday, April 27, 2012

Another sampler pack.

I became one of those shooters that brings a logbook to every range trip so gradually I hardly noticed it...

But it's vital for handloading, especially if you use a chronograph. I also can see the benefits for practicing and recording your own performance and any malfunctions. So it's a practice I recommend heartily.

I took my 255 grain castings from yesterday and made up four lots of five.

From left to right: Winchester Silvertips, Buffalo Bore Lead Round Nose Flat Top, Powerball, Federal round ball, hand cast 255 grain, and hand cast 230 grain. In background is a cylinder of more 255 bullets and 2 100 count red boxes of spare handloaded cartridges.

This was to fill out the matrix of two different overall cartridge lengths and two different powder grain loads. So when I'm at the range I'll be able to get velocities of each lot and should be able to separate the affect of each on that particular load.

(Okay technically I made up 3 of those lots today, as you can see in the picture I had some of the "baseline" configuration already made).

Overall length has an effect on the velocity of the bullet via two mechanisms. The deeper you seat the bullet the more force is required to remove it on ignition, also the deeper the seat the less initial volume there is within the case upon ignition. The question of how much seating depth effects velocity (and pressure) depends on a host of factors from case and bullet geometry, to case crimp style, to powder burn rate, to primer type. But at least with this particular load out I should be able to get something of an idea of the effect at work.

The effect of powder on velocity should be clear enough. Though again the effects are non-linear and there are considerable contributing and limiting factors. Also keep in mind all the redline limits on your load data and take care with your loads so you don't have something go wrong.

Also in a previous session, I sized some of my 230 grain castings and did them with the standard powder charge and overall length and will compare them to the unsized ones from a previous lot. This will tell how bullet diameter (0.452" versus 0.451") will affect velocity. Again for this particular load.

I'll note that my 230 grain castings don't need resizing to be assembled into a cartridge, but my 255 grain castings do. This is because the larger diameter profile on the 255 grain bullet actually prevents headspacing if not resized.

I also have some factory defensive loads to test. And some factory plinking loads to test for calibration and the effect of barrel length on velocity.

I should have realized what would happen when an engineer gets into handloading. And yes I realized that sample sizes of 5 are quite small, but this is just preliminary work.

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