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Old 04-19-2012, 06:01   #31
Buffalobob
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Join Date: Aug 2006
Location: Potomac River
Posts: 925
As I mentioned in post #34 I would try to test the transonic stability of the bullet. This has finally happened and as luck would have it the test weather conditions were pretty raggedy but I shot anyway.

Because I do not have access to a 1500 yard range I decided to develop a reduced velocity load that would go subsonic at about 700-750 yards. One of my loading manuals had a starting load for 175 grain bullets and Varget so I put together a load with a muzzle velocity of 2250 fps. This load was tested for accuracy at 100 yards by firing two groups from the bench. Groups size CTC was less than 0.4.

Ttransonic stability was tested during a F-class match at R4 Quantico USMC. There was the worst headwind I have experienced in the last six or seven years. It was about 20 mph and varying from 10:00 to 2:00. During the unlimited sighter stage at 800 yards the rifle was zeroed for the 155.5 Berger (MV= 2800fps) that I normally compete with and also the 175 OTM (MV-2250fps). The 800 yard stage was fired with the 155.5 Berger and produced an average per shot score of 9.3 which was probably the best score I have ever gotten at that stage. The “open” rifles were averaging about 9.0. But what I got was a period of wind that stayed at 11:00 so I didn’t have the direction switches that are so damaging to the score. So the test was off to a bad start being as I had shot about 5 points better than normal under some of the worst conditions.

At 900 yards I used the 175 OTMs and got a per shot average of 7.3 being as the wind was back to switching direction. At 1000 yards I went back to the Berger 155.5 and got a per shot average of 6.75. Those of us shooting “FTR” (308) were recording misses off of both sides of the target because the wind was so unpredictable. The interesting thing is that the subsonic, slow moving 175 OTM produced a higher per shot score than the faster supersonic 155.5 Berger at the 100 yards difference --- 7.3 vs 6.75. This is about a half MOA difference.

So I conclude that the 175 Berger even when it is well below the transonic zone still retains very good accuracy.

For those who forgot, I tested terminal performance of the 175 OTM at normal velocity on a deer in this thread.


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