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Grading 8mm Bullet Jackets
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Old 04-12-2015, 03:03 PM
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Default Grading 8mm Bullet Jackets

In this thread http://thehunterslife.com/forums/sho...hlight=bullets I found out that the jackets I had received from Hawk varied considerably in weight. Somewhere in the vicinity of 3 grains from lightest to heaviest. That was disappointing and frustrating because the swaging equipment produces a very consistent and precise core. Were the jackets equally as precise, finished bullet weights would be much tighter in their weight variation.

After mulling it over for a bit and considering the options available, the only reasonable solution seemed to be to grade the jackets based on weight then adjust the core weights accordingly to give the target finished bullet weight. Given the fairly wide weight range, that meant I would have to weigh each and every one of them. Resigned to that, I decided to start the grading process.

The weight range is 40.2 grains through 43.6 grains. However, the vast majority fall between 40.8 and 43.4 grains, and the distribution is bimodal with nodes at 41.6 and 43.1 grains. The following pictures are worth a thousand words of explanation:


And further along on a different batch:


All tolled, I weighed 408 jackets. Here is a histogram of the counts by 0.2-grain increments.

Actually, I think 0.2 grains is too fine a detail, but one has to go to a high level of precision to determine how high a level of precision is required.

Here's a table illustrating what the finished weights would be if I used the jackets with weights from 40.8 to 42.2 grains and set the core weight based on the average jacket weight.
Looking at the columns on the right, you can see that for a desired finished weight of 125 grains, the finished weight range would be 124.3 to 125.7. That's tolerable to me, but, I can do better than that without much more work.

I have put all of the jackets in separate containers based on their weight. It is relatively easy to set the core swaging die up to produce cores weights within 0.1 grain. Therefore, if I adjust the core weights for each 0.2 grain increment in jacket weight instead of using the average jacket weight, I should be able to produce uniform bullet weights within the variability of the jacket weights - 0.2 grains. For example, in 125, I should theoretically be able to produce finished weights of 124.8 to 125.2 grains. In practice, it will probably be more like 124.75 to 125.25 - about half a grain. I'm fine with that.

Adding another component like a plastic tip, will introduce variance up to the level of variance in the new component's weight. At this point, I'm not willing to pay for the Talon points, and I haven't worked out the bugs with the printed points or the turned delrin points, so it looks like the first few hundred bullets will be HPs or Spitzers, depending on the finished weight.

Paul
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8mm, anvb, bullet jacket, swaging


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