In this thread http://thehunterslife.com/forums/showthread.php?t=16677&highlight=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

G'day Paul.

I use the same method to grade the 155gn BTHP projectiles into 0.2gn increments for use in my 7.62mm Omark target rifle. I also grade the Lapua cases based on weight (I know there may not always be a correlation between weight and volumetric capacity, but it is easier and less fiddly).

In F-class we get 2x sighter shots ( to enable adjustments for windage and elevation for the changes in range) followed by 10 scoring shots. I try and enure that I have 12x cases loaded with projectiles and cases in the same weight ranges. Variation between the 12x case lots is catered for by the sighter shots. Any outlier projectiles/cases I use for zeroing scopes, giving friends a go, practice and the like.

How much difference in POA are you likley to see with the variation in your 8mm projectiles? Maybe you could group by weight as you have, but then just load and shoot in those groups.

Or maybe you need a few inside activities you fill in those long cold winter days....

Marcus

Interesting, Marcus. I didn't know you shot F-CLass. I'm pretty much on board with all you have said.

I decided to go ahead and make some bullets and test the paper-whipping. I like to 'crunch numbers' because it gives me a feel for what's going on. Helps me troubleshoot problems too. However, there's no substitute for "doin' it", and that was the case this afternoon. I started setting up the press and dies to start making cores. To keep it short, because the handle of the press hits the floor before the press cams over, AND because I have 'ruptured' my bench with the swaging press, it's currently difficult to get a consistent stroke. Therefore, I get a range of core weights of about 0.5 grains.

So, sighing a heavy sigh, I started grading the cores. After I had 10 of them made, I thought it time to match the cores with the jackets. At first, I was of course weighing each and putting them together. That was 'dissatisfying'. :cens: Then it dawned on me that I was making it more difficult than necessary. All I needed to do was get a core and start putting the core in the jackets from the appropriate bin, (the one where the sum of the weight of the jacket and the core yielded the desired bullet weight). I tried jackets until I got the exact weight I was after. In this case, 123.5 grains. Doing that, I made 10 bullets.

Upon completion, I weighed all of the bullets individually, and all came out exactly 123.5 grains. No variance within the level of precision of my scale - 0.1 grain. :grin: Then I put them all in the pan and got their cumulative weight -1,235.1 grains. That means of course that their individual weight shouldn't vary my more than 0.01 grains per bullet. Of course there could be larger errors up to 0.05 grains that cancel each other out, but I'm pleased with getting weights as 'tight' as this. VERY pleased.

That's the 'good news'. Of course a 123.5-grain bullet with a diameter of 0.323" doesn't have much of a caliber-sized bearing surface. In fact, it's only 0.150". That's less than 50% of caliber. I try not to seat bullets less than 67% of a caliber deep into a case. The bullet is 0.712" long. That means that there is 0.562" of "nose". Doesn't sound like a "stable" bullet to me. In fact, what it does sound like is a perfect bullet for a sabot. But then nobody makes sabots for 8mm bullets. (Like a .338 caliber sabot with an 8mm cavity.)

Anyway, I think I'm going to shoot for something in the 140-grain class. That should give me a reasonable bearing surface and a good exposed-lead nose. I'm thinking about it's use in the AR-10 in an .308 Win case. The 8-08.

Pictures at ll.

Paul