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Old April 22, 2014, 12:49 PM   #1
taliv
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experimenting with SD and ES

following this thread http://www.thehighroad.org/showthrea...64#post9445564
i would like to invite people with chronographs to repeat a few tests and report your SD/ES before and after

i know everybody reloads differently and lots of people get great results doing things radically different. but for low ES, this is what I think is important in order:
  • consistent powder charge
  • consistent ignition
  • consistent neck tension

I think case volume is also important, but to a lesser extent. I say that because while I get the best numbers with Lapua brass, I usually use blemished hornady or RP brass because they're almost as good for a fraction of the price. I don't prep the brass at all*. I don't own a flash hole deburring tool or primer pocket cleaner. I don't trim necks, etc. However, I did neck turn at one point but now i do no-turn necks.

For powder, i use an acculab scale (i think they're called sartorius now) and measure to the kernel of powder. a given kernel of extruded powder such as H4350 tends to be .01 - .02g and the scale's precision is to .02g.

For consistent ignition, the important thing to me is seating the primer correctly, not cleaning the pocket etc. make sure it's fully seated so the anvil compresses.

With those two out of the way, I want to spend a minute on neck tension and the experiment i'm proposing.

My postulate is that consistent neck tension is important and the less you have the easier it is to be consistent. Taken to its extreme, zero neck tension is the easiest to achieve consistently. i.e. if the projectile slides freely back and forth, it will be the same for all shots. In my experiments, this seems to be true and I get the best SDs and ES when i can move the bullet in the neck easily with even light finger pressure. obviously, this is not useful for practical shooting and care has to be taken not to dump powder in your action etc. So what I do is attempt to minimize nk tension in two ways. First, I use FL bushing dies so i can control how much i size the neck and only put 1 thou tension** on, and second, i only screw the cap on halfway so the die is only resizing the body and the top half of the neck. ime, if i can put the round in the chamber and pull it out without leaving the bullet stuck in the lands, there's enough tension. anymore is too much.

So here's my challenge:
make a control and test set of ammo and run them over your chrono, alternating rounds from each group.
control is your normal load. test set is zero neck tension. how you do that is up to you. figure it out. maybe you just don't resize your brass at all, or if you have a FL bushing die, just remove the bushing so you size the body but not the neck.

report back on your results.




*since i'm shooting a 260AI from 243win brass, i am technically necking up and then fireforming. just not bothering to sort cases and do all that other prep. who has time?

** by that i mean, i measure the OD of the neck, then seat a bullet and measure it again. the second measurement will be 0.001" more than the first
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Old April 22, 2014, 04:43 PM   #2
Andrew Leigh
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I will bite but not right now. Getting ready to throw QuickLOAD at my 6.5 and 30-06, powder and bullets are on their way as well as my Wilson seating dies.

Personal observation. The worst change in SD I have EVER got was from 5fps to 25fps load to load. I decided to anneal my .375 brass, my first time annealing, needless to say it was a disaster. I could feel the varying neck tensions on seating and knew I was in for a long day, I was not wrong.

I have had more poor results from poor F/L sizing technique and from varying neck tension than any other. I load and shoot sequentially so the place each round in the box occupies is known to me. On seeing odd results I go back and can check case weight, capacity, length etc. for any given Chrony speed recorded. I am able to correlate notes I have made i.e. on seating seating etc.

The ones that really have made the difference have been neck tension (I need neck tension as I magazine load as a hunter and need to circumvent setback). The other one has been case volume. The weights of top bullets are close enough and the results from decent scales close enough for me, and I only weigh to one decimal place. Would love to seat on the lands on closing the bolt.

My annealing machine is 60% complete.

Have you ever considered following Dan Newberry's load development shot sequence? This may remove some of these spurious results?

Load 1 - Shot 1 - Target 1
Load 2 - Shot 1 - Target 2
Load 3 - Shot 1 - Target 3
etc.

So you lay down the first shot of each load in a round robin fashion on their own targets before repeating the sequence for shot 2 for each load and then Shot 3 and so on. What this does is my opinion is to remove barrel heat as a criteria and caused one to focus on every shot.

Let's say that there is movement through temperature and any other variable, these shifts are duplicated in the 2nd, 3rd etc. shot sequences providing they are shot within the same time frame. So the group POI may shift from target to target if on the same load but the group size should remain the same size.

Does that make any sense?
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Old April 22, 2014, 05:52 PM   #3
USSR
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taliv,

Did it 10 years ago when I started shooting competitively. Myself and everyone else I shot with discovered: Lapua brass + ~0.01" neck tension = low ES and SD numbers.

Don
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Old April 22, 2014, 07:28 PM   #4
Walkalong
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Light neck tension and good brass is the way to go. Do the math on light neck tension variations vs heavy neck tension variations. Use being close to the lands to help start pressures, and/or more powder to get the pressure needed for a good burn.
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Old April 22, 2014, 07:51 PM   #5
taliv
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yep, don, but i'm using crap brass with no prep and 1/10th your nk tension
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Old April 22, 2014, 08:35 PM   #6
USSR
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taliv,

When I said ~0.01" neck tension, I meant very light neck tension. No way really to accurately measure it. That you are getting good results with inexpensive unpreped brass is great.

Don
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Old April 22, 2014, 10:21 PM   #7
ironworkerwill
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I got a real problem! I can't seem to make myself stop trimming brass all to the same length and sort by times fired and weight within range. Not to mention scrapping primer crud out of the pockets. I'd have to get more brass for a proper experimentation.
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Old Today, 11:08 AM   #8
spitballer
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Yet another interesting thread - this time I've been motivated to revisit some of my original experiments in allowing the lands to seat the bullet.

After much tedious neck sizing I've got a box of 50 cases that are "finger tight". That is, loose enough to move with my fingers but snug enough to withstand inadvertent bumping while being fed.

Next problem will be how far to over-extend to insure seating every time. I'm thinking at least .015"-.020" for genuine consistency with a case neck that's snug. How far are you over-extending your bullets with the loose necks?
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Old Today, 11:19 AM   #9
USSR
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Quote:
...I've been motivated to revisit some of my original experiments in allowing the lands to seat the bullet.

After much tedious neck sizing I've got a box of 50 cases that are "finger tight". That is, loose enough to move with my fingers but snug enough to withstand inadvertent bumping while being fed.

Next problem will be how far to over-extend to insure seating every time. I'm thinking at least .015"-.020" for genuine consistency with a case neck that's snug. How far are you over-extending your bullets with the loose necks?
spitballer,

When I was loading them into the lands, I would use 0.001" or less neck tension (sounds like what you are doing), and would seat the bullet so that it was 0.020" into the lands. Chambering a round would then seat the bullet further into the case. Should you chamber a round and want to remove it without firing it, remember to hold your rifle with the muzzle pointed skyward so that should the bullet come out of the case during extraction, you won't dump the powder in your action.

Don
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Old Today, 11:46 AM   #10
taliv
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looking forward to your results!

when mine were that loose, it didn't seem to matter. but then, i'm also shooting berger hybrids so they aren't nearly as jump sensitive anyway. i'd seat them to my normal depth (just shy of lands) but they'd move around some on their own so they weren't consistent depth by the time i shot them
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Old Today, 12:15 PM   #11
Walkalong
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I used just enough neck tension that you could not spin the bullet or push it deeper with no effort. I was a bit deeper into the lands, closer to .030, although I did not measure it. This was with neck turned brass and a tight necked (.262) chamber.
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