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Joined: Jul 2003
Posts: 437
Campfire Member
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OP
Campfire Member
Joined: Jul 2003
Posts: 437 |
Can the poi change vertically besides velocity change?
I went to the range checking two loads. Both are 140 grain bullets, one is a TSX and the other is a accubond. Both loads are around 3200 fps. I haven't got a chance to re-check the accubond on the chronograph since going up a 1/2 grain on the powder charge but I am pretty confident that the loads are no more than 25 fps difference in velocity.
What I found was that the Accubond was 1 inch lower and 1.5 inches to the right of the TSX. I was a little surprised at the difference of impact but also that the accubond was shooting 1 inch lower at 100 yards.
What do you think?
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Joined: Jan 2001
Posts: 29,851
Campfire Ranger
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Campfire Ranger
Joined: Jan 2001
Posts: 29,851 |
Nothing unusual at all when 2 types of slugs give one different points of impact.
1Minute
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Joined: Jul 2003
Posts: 437
Campfire Member
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OP
Campfire Member
Joined: Jul 2003
Posts: 437 |
It sure would be nice to have loads that group close to the same impact so I don't have to change scope adjustments. I have 150 grain loads going 100 fps less that are closer to the TSX POI. I've been told that different bullets give off different vibrations from different pressure spikes so basically all loads are going to be different unless your lucky.
The thing that bums me is my two 140 grain loads are not going to be on the same scope adjustments for elevation. The accubond with the higher BC is shooting a inch lower. Bummer
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Joined: Jan 2008
Posts: 589
Campfire Regular
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Campfire Regular
Joined: Jan 2008
Posts: 589 |
One difference could be the ballistic coefficient of the bullet. And, I agree that different bullets do behave differently. Don't have a good explanation as to difference in left right, but it does happen.
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Joined: Oct 2009
Posts: 1,784
Campfire Regular
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Campfire Regular
Joined: Oct 2009
Posts: 1,784 |
not an expert AT ALL, but from what I understand the Accubond might have a flatter trajectory and hence has less "gain" in altitude at 100yds (relative to your scope). But most likely it has to do with the harmonics and effects of different bullet materials on the barrel.
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Joined: Oct 2004
Posts: 4,340
Campfire Tracker
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Campfire Tracker
Joined: Oct 2004
Posts: 4,340 |
I worked up a load for a buddy's 300 wsm this summer using 168 ttsx's and 168 nosler J bullets. With identical powder charges they clocked identical speed. (A little surprising since the tsx is hugely longer and monolithic but apparently prove the grooves work). Anyhow both consistantly shoot great and both consistantly shoot to a diff point of impact. Sure would have been fun to give him a practice load that was identical cause even the bc's are nearly the same. Just doesn't work out that way often.
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Joined: Oct 2010
Posts: 298
Campfire Member
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Campfire Member
Joined: Oct 2010
Posts: 298 |
I believe the barrel resonance and the amount of time the bullet is in the barrel as the gun kicks back and the barrel rises. I know that some of my buddies hand loads in his rifle will shift depending upon the weight of the bullet, as much as 12 inches. In my 223 with different bullets of the same weight the point of impact is usually laterally different, as much as 4 to 5 inches. You can also look at the data on this link. You will notice that the charges are all the same, and the velocities are not. http://www.shootingtimes.com/ammunition/ST_newpowdersbullets_040510WO/index.html
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