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Old November 4, 1999, 11:55 PM   #1
Bob
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Join Date: April 29, 1999
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I have recently been experimenting with the Combined Technology moly ballistic tips in my Model 7 .243. I went to the range to see how these loads compared to my Sierra HP's and soft points. After shooting several groups with my normal loads I decided to see how the moly's acted. I was very surprised to see that each 5 shot group hit consistenly 2 inches high and 2 inches right. I can understand the elevation, but the loads drifting 2 inches right on a perfectly still day has been baffling me. I am fairly new to reloading so maybe this is a common occurence that I have just not encountered.
What I'd like to know is has anyone else experienced this?
Is there a remedy to the drifting other than adjusting the scope each time I go to shoot these rounds?(yeah I know, just hold left huh)
Thanks,
Bob
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Old November 5, 1999, 12:20 AM   #2
Mal H
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Bob,
That's not an uncommon occurrence when changing ammo. I think you're seeing the difference in the resonance of your barrel. I assume you mean a Remington Model 7 which has a shorter barrel than the Model 700, for example. I believe you'll see this occur with shorter, lighter barrels more often. If you had setup the rifle for the CT moly's first, you would be wondering why the Sierra's are shooting to the left. If you want to see this in spades zero a Ruger Mini-XX and then change ammo.
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Old November 7, 1999, 05:46 PM   #3
WalterGAII
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MalH is right on the money. I just got through shooting some various loads through my .223 Rem. VS. I was shooting the same weight bullets, but some of them were Blitzkings, some V-Max, some Ballistic Tips. They all had different points of impact, not just in elevation, but also in windage.

You simply have to zero your scope for whatever round you're going to depend on.

BTW, my Glock21, shooting .400 Cor-Bon, shoots significantly higher and flatter than when I'm shooting .45. I just have to adjust my sight picture to compensate. (Also shoots a little to the left with the .400 Cor-Bon.)

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Old November 7, 1999, 07:58 PM   #4
HankL
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It's called barrel harmonics. If that load shoot good for you then adjust your zero.
Hank
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Old November 9, 1999, 07:24 PM   #5
orsogato
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Bob,

If all the rounds are grouped tightly. Change your scope real subtle like and watch em all go in the bullseye.

Hehe, I dont mean to rag on you. Just pokin a little fun thats all. What the previous responses all point out correctly is the simple fact that different bullets shoot differently.

Find a load that groups tight, adjust the sights to where you want them to hit (ex. I typically sight in my 06 about 2 to 2.5 inches high of bullseye at 100 yards). AND LET EM RIP.

Orso.
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Old November 9, 1999, 07:39 PM   #6
Bob
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Thanks for the help guys. For now I'm going to shy away from moly's, I seem to get better groups for non-coated bullets. Probably just need to try some different powders and seating depths, but theres no time right now.

Thanks again.
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Old November 9, 1999, 07:51 PM   #7
WalterGAII
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There's nothing wrong with moly. I don't shoot anything but moly in any of my rifles.

What you don't do is shoot moly behind copper without a thorough cleaning first. Then you have to fire fifteen or twenty moly rounds for the barrel to become moly coated. Only after that will your groups be right. I've tried moly barrel preps with various results.

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Old November 9, 1999, 11:55 PM   #8
Long Path
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We noticed the same thing when loading identical loads in .257 Rbts of Speer 100g spitzers and 100g Nosler Ballistic Tips. The rifle was regulated for the Speers, and we were just checking to see if there was a group size change at 100 yds. Not much of one, but the groups moved up and to the right by about 2.5"!!! The change in height absolutely could not be accounted for by the better ballistic coefficient. .25" I could understand, but not 1.5" or better! Then there was that huge jump to the right. Harmonics, I would guess. This surprised me, because this barrel's contour is described as "semi-varminter," and is really pretty heavy. I wondered at the time if the difference in ogive, etc might cause the bullet to engage the rifling different, causing different air friction and Cornelius effect and... and...

<sigh.>

Yep, let's call it barrel harmonics.

L.P.

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Old November 10, 1999, 01:48 AM   #9
Cheapo
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Yup, the Cornelius effect from Planet of the Apes. That's the tendency for any sound scientific idea to be roundly rejected by the political powers that be.

Don't think I can even spell Coreolis Effect properly.

An often forgotten element of barrel dynamics is recoil torque as applied to the rifling twist. As the barrel is hummin' and wigglin', there's a bit of a itsybitsy twist as the bullet gets rotated in one direction and the barrel starts to move in the other. Kinda like your muscle car being rocked opposite the engine rotation when you rev it.

Even stiff Varmint barrels have a bit of barrel whip. Launch the bullet so it leaves at the high end instead of the low, and you'll have a change in where the group centers.
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