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Reloading PPU bullets

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Shamu View Drop Down
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    Posted: November 25 2017 at 2:38pm
Tried test firing the 180 Gr PPU SP/BTs today, the Varget was again lackluster.
39,0 Gr gave a weak 2121FPS @ 15'. I made up 3 ladder loads a 38.0gr, a 38.5 gr & a 39.0 gr.
 average performance was 56.4 FPS per gr.

Using that load density I'd need an insane 41.69gr to get 2350 FPS!
Confused

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SW28fan Quote  Post ReplyReply Direct Link To This Post Posted: November 27 2017 at 5:37pm
I have a great preference for the  Sierra 180 grain flat base.  Boatails  have always given me spotty performance
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: November 28 2017 at 4:09am
Do you expect the velocity difference per grain of powder to stay the same as you increase the load?
Would the increase in powder volume and decrease in air gap behind the projectile increase the velocity by a larger amount each time. It's just a thought. Which rerquires verification of course.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: November 28 2017 at 5:35am
Within reason, yes. As you approach max it gets less linear, but with mid range loads it seems to be pretty constant.

A few years back I did some tests, working up ladder loads & it seemed to hold true to the point I could predict where it was going.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: November 28 2017 at 12:11pm
That's interesting. I'll bear that in mind when I'm working on a change in powder. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: November 28 2017 at 2:08pm
I'm not sure how well this will reproduce, reduced for the forum, but at full size its pretty legible.

Let me explain a bit:

The Horizontal axis is calculated from the manual, or chronographed velocity.

The Vertical axis is charge weight.

The various red solid horizontal lines are min/MAX charge weights from several different manuals.

The horizontal red dashed line is the median between lowest HIGH & Highest low.

The SOLID diagonal lines are book load density/velocity.

The dotted or dashed ones are actual velocities found by testing.

The vertical red lines are nothing to do with the work up, but they are ballistic aims for an auto-ranging scope, & so are aims I'd like to match as there are only so many range drums available.

What I do is to draw the various reloading manual  min/MAX loads. Then I graph a min/median/MAX

Then I load up 10 rounds at the lowest MAX, The Highest min, & the median halfway between them. (this gives me a decent spread & is as safe as I can make it by ONLY using the most cautious load data.) This give me a 3-point graph data-set. Then I fire them over the chrony, documenting as I go, those are the dotted or dashed diagonal lines. This offsets the published book data with the actual performance of my rifle & bore.

In this case ( a .308 win with a 168Gr Sierra HPBT(M) & WW748 the min is 44.25, the median is 44.8 & the max 45.3gr) As you can see the book data is very linear, the strait line portion of the graph. The actual chronographed values are a little more variable (look at the green line for the 168Gr Sierra HPBT(M) you can see the dogleg where its passes the 43.25 gr level).

To use this all you do is follow the graph to where you either find the desired charge weight & look up the velocity, or vice versa, As long as the intersection is within the limits of the min/MAX charges you can load it up & test fire to confirm. In this case I used the conservative load data to compare a 165Gr HPBT GameKing as well ( the lower green line) as the 168Gr MatchKing.

That's 30 rounds one range trip & a reusable resource that's good for years!





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2017 at 7:53am
Update
I went for another work up, a little higher this time as I wasn't happy with the velocities I was getting. I usually like something a bit under 100 FPS less than listed max as it seems to be a sweet spot for accuracy in several calibers.
Results when chrono'd were interesting to say the least!
I went with a ladder workup as described earlier 38, 39, 40, & 41 Gr of Varget under the 180 Gr Prvi Partizan SPBT.

38 , 39  , 40, & 41 gr respectively
AIM Low High AVG E.S. S.D.
2300?? 2099.37 2141.33 2121.79 41.96 18.52
2400?? 2190.94 2237.51 2218.73 46.57 21.42
2250? 2220.00 2303.00 2252.00 83.23 32.04
2350? 2285.00 2380.00 2333.00 95.27 33.82

Its interesting how there's  such a steady increase in variability as the load increases.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2017 at 11:22am
Shamu; I've often had the odd unexpected change in velocity when testing. Even though I have been quite sure of my loads. So try to work with the averages. Now I use an electronic powder doser, which is better than my old method of doing it by hand and zeroing each case prior to filling.
I have a batch of PPU ogives to reload. They appear similar to the SB type 180 grains. The weights are variable when compared to the Sierra Match Kings.

I have not had time for any reloading recently; and no heating in the shed so winter is not the most enjoyable time to be in there.
Looking forward to working up some loads for the Maltby No4Mk1. Not sure if I'll be able to improve on the factory ammo though. That seems really good in this rifle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2017 at 1:24pm
The averages are about what I expected 70~85 FPS/Gr. Its the variances within a string expanding that has me baffled!
41> 46> 83> 95!

I think I'm going with 39.0 as I don't like ES over 50 or SD over 20 or so.
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