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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
338 Allen Xpress, first load developement session....
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<blockquote data-quote="Fiftydriver" data-source="post: 162093" data-attributes="member: 10"><p><strong>Ballistic mysteries continue....</strong></p><p></p><p>I am not sure if this bullet is just taking us to such a different level of ballistic performance that the old ballistic calculators are not working or what but I have run into some seriously strange things again as I did with the 338 AM testing this bullet.</p><p> </p><p>First off, consistancy is great, accuracy is great, getting the ballistic model to match up to actual bullet flight, nearly impossible. Let me explain.</p><p> </p><p>Went out this morning with 20 rounds of test ammo. I used 98.0 gr Retumbo under the 265 gr AL RBBT which averaged right around 2965 fps this morning. Extreme spread was in the mid teens.</p><p> </p><p>Bore sighted the rifle and after a couple shots was where I wanted to be. Made one more slight adjustment and then shot a three shot group at 100 yards on paper. This group was right at 0.7" with the last two touching. The center of the group was 1.9" high at 100 yards.</p><p> </p><p>Went back to 450 yards, shot a three shot group. Nice group, just a hair over 2" which for a 9 lb class rifle I am plenty happy with. Group center was just a hair over 16" low. This matched up perfectly as my first mil dot down was used for the hold and the mil dot pretty much covered up the group.</p><p> </p><p>I then turned the rifle on a 2.5 gallon water jug that was looking at me wrong that I had placed backed up against one of the logs on my backstop. The jug was blown forward 15 feet from the impact!!! Which was dead center using the first mil dot down.</p><p> </p><p>Came back to my computer to run the numbers, </p><p> </p><p>2965 fps</p><p>1.5" scope height</p><p>65 degrees</p><p>45% humidity</p><p>3300 ft altitude</p><p>26.82 Bar press</p><p>240 yard zero</p><p> </p><p>I used a BC of 0.900 and ran the numbers. 100 yard impact was predicted to be +2.0". Very close, within group variations.</p><p> </p><p>Then the mystery, the predicted drop at 450 yards was right at 21". It was far less then this.</p><p> </p><p>I increased the BC to 1.05 and still the predicted drop at 450 yards was said to be just a hair over 20".</p><p> </p><p>How in the hell is my rifle shooting nearly 4" flater then this at 450 yards???? </p><p> </p><p>I had to go back out and recheck the zero so I shot three more shots at 100 yards which this group measured 0.455" ctc and again right at 1.9" high for the center average of the group.</p><p> </p><p>Put one more water jug up and moved back to 450 yards and again water flew with a very center hit using the first mil dot down. Now from my figuring, one mil is 3.6" per 100 yards so that comes out to 16.2" at 450 yards.......................</p><p> </p><p>I think I need to come back and look at this again with fresh eyes, I must be missing something simple. What do you boys think. ARe we just dealing with a bullet with a higher BC then we have played with before and the ballistic models are not matching up.</p><p> </p><p>I even tried using the G7 drag function with no more luck then the G1 out to 450 yards.</p><p> </p><p>I must be missing something simple here. Open my eyes.</p><p> </p><p>The rifle shoots like a dream by the way, there will be an elk in serious trouble here at the end of the month!!!</p><p> </p><p>Kirby Allen(50)</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 162093, member: 10"] [b]Ballistic mysteries continue....[/b] I am not sure if this bullet is just taking us to such a different level of ballistic performance that the old ballistic calculators are not working or what but I have run into some seriously strange things again as I did with the 338 AM testing this bullet. First off, consistancy is great, accuracy is great, getting the ballistic model to match up to actual bullet flight, nearly impossible. Let me explain. Went out this morning with 20 rounds of test ammo. I used 98.0 gr Retumbo under the 265 gr AL RBBT which averaged right around 2965 fps this morning. Extreme spread was in the mid teens. Bore sighted the rifle and after a couple shots was where I wanted to be. Made one more slight adjustment and then shot a three shot group at 100 yards on paper. This group was right at 0.7" with the last two touching. The center of the group was 1.9" high at 100 yards. Went back to 450 yards, shot a three shot group. Nice group, just a hair over 2" which for a 9 lb class rifle I am plenty happy with. Group center was just a hair over 16" low. This matched up perfectly as my first mil dot down was used for the hold and the mil dot pretty much covered up the group. I then turned the rifle on a 2.5 gallon water jug that was looking at me wrong that I had placed backed up against one of the logs on my backstop. The jug was blown forward 15 feet from the impact!!! Which was dead center using the first mil dot down. Came back to my computer to run the numbers, 2965 fps 1.5" scope height 65 degrees 45% humidity 3300 ft altitude 26.82 Bar press 240 yard zero I used a BC of 0.900 and ran the numbers. 100 yard impact was predicted to be +2.0". Very close, within group variations. Then the mystery, the predicted drop at 450 yards was right at 21". It was far less then this. I increased the BC to 1.05 and still the predicted drop at 450 yards was said to be just a hair over 20". How in the hell is my rifle shooting nearly 4" flater then this at 450 yards???? I had to go back out and recheck the zero so I shot three more shots at 100 yards which this group measured 0.455" ctc and again right at 1.9" high for the center average of the group. Put one more water jug up and moved back to 450 yards and again water flew with a very center hit using the first mil dot down. Now from my figuring, one mil is 3.6" per 100 yards so that comes out to 16.2" at 450 yards....................... I think I need to come back and look at this again with fresh eyes, I must be missing something simple. What do you boys think. ARe we just dealing with a bullet with a higher BC then we have played with before and the ballistic models are not matching up. I even tried using the G7 drag function with no more luck then the G1 out to 450 yards. I must be missing something simple here. Open my eyes. The rifle shoots like a dream by the way, there will be an elk in serious trouble here at the end of the month!!! Kirby Allen(50) [/QUOTE]
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338 Allen Xpress, first load developement session....
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