Jacket hardness and bullet deformation

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
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Cedar Springs, MI
#1
Anyone have data/web resources on jacket hardness/thickness? I've got a 3 groove barrel in .264 that has an interesting phenomenon occuring: 123 ELDMs shoot great when barrel is clean to moderately fouled (100 rounds or so) but then groups open a bit. However, 123 SMKs seems to shoot okay when clean but seem to shoot much better past 100-150 rounds.

I'm wondering if jacket hardness as related to bore tightness/fouling has something to do with this. I'm planning to test this theory at 1000-1200 yards to see if there is a statistically significant relationship. Basically, I want to shoot the thinnest/softest jacket, medium thickness/hardness jacket and thickest/hardest jacket with both a 3groove and 5R style barrel. Currently have the following bullets: 123ELDM, 123 Scenar, 130ArHybrid, 140 VLD Hunt, 130TMK.

Willing to buy others and would like to find 3 bullets in same weight class 123/130/140 with different relative jacket types. Will be shooting in clean barrel, then again at 100 round count and 200 round count. Goal is to see if I can find jacket types that is more consistent over time rather than need to thoroughly clean every 100-150rounds.

Any help (or experience on subject) would be greatly appreciated.
 

TripleBull

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Feb 13, 2017
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#2
I have not verified the claim but I read an ammo comparison test that claimed that it takes at least 10 rounds to "condition" a barrel to a different jacket when switching from one ammo to another. Whether or not that claim is accurate, you should think about the procedure you'll use between different bullets in terms of cleaning or the number of rounds for each bullet test. I'd want to shoot multiple group repetitions just to get more data on reproducibility.

Then again, I rarely avoid the opportunity to shoot too much.
 
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Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
314
85
28
Cedar Springs, MI
#3
I have not verified the claim but I read an ammo comparison test that claimed that it takes at least 10 rounds to "condition" a barrel to a different jacket when switching from one ammo to another. Whether or not that claim is accurate, you should think about the procedure you'll use between different bullets in terms of cleaning or the number of rounds for each bullet test. I'd want to shoot multiple group repetitions just to get more data on reproducibility.

Then again, I rarely avoid the opportunity to shoot too much.
I was planning to shoot 2-10 round groups of each with other to continue fouling bore between test sessions. But may be difficult to isolate variable if I'm shooting in vastly different conditions. Ideally, I'd shoot each group in round robin style (1 group each, cooling between then repeat) to keep test relatively quick. Groups likely at 500-600 and 1000 .
 

Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
314
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Cedar Springs, MI
#4
But I'm concerned about wind affecting results too much at 1k. Ill probably run test at distance where wind variability will result in less than .3MOA differential. Above that and it makes testing very hard. So that would leave it at about 3-400 with a +-1 mph wind call at full value. Head or tail wind will increase that range by nearly double.
 

TripleBull

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Feb 13, 2017
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#5
But I'm concerned about wind affecting results too much at 1k. Ill probably run test at distance where wind variability will result in less than .3MOA differential. Above that and it makes testing very hard. So that would leave it at about 3-400 with a +-1 mph wind call at full value. Head or tail wind will increase that range by nearly double.
I hear you. Testing precision at 1K is so hard on my ego, I tend to avoid it. You can always just isolate on vertical dispersion as your measureable.
 
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Subwrx300

Mastery: its difficult for a reason....
Jan 15, 2014
314
85
28
Cedar Springs, MI
#6
That is a
I hear you. Testing precision at 1K is so hard on my ego, I tend to avoid it. You can always just isolate on vertical dispersion as your measureable.
That has crossed my mind. Challenge is to ensure SD is similar between each round type or be able to quantify difference be target.

I think I'm seeing softer bullets/jackets deform unevenly after bore is very dirty whereas harder/thicker jackets fight through the crud and maintain good uniformity with fewer flyers. Just thought it would be a good test for a gas gun as the gas port seems to take a bit of copper of the bullet on its way out.
 
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