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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
How to check a Chronograph?
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<blockquote data-quote="TexasHunter" data-source="post: 566112" data-attributes="member: 26082"><p>Hey Wile,</p><p></p><p>During the load dev and testing of the one mile rifle we built for NTRP, we used a beta and a CED to test loads. With the exact same load, the Beta gave us around 3175 fps and the CED gave us around 3000. Both units were set up at the same bench at the exact same distance. All reloading components were the same as was the load itself. We were developing loads for the 300 RUM using the Hornady 225 grain match. We really needed around 3100 fps to get to the mile with the 225. Needless to say, we were scratching our heads. I called Hornady to confirm the BC of the 225 and they told me .670 G1. My client, Josh Ruby of NTRP had used this bullet extensively in a 300 WinMag and believed it to have a BC more close to .690.</p><p></p><p>So the following weekend we went to his 1780 yard range to test rifle and load. We were getting an SD of 5 from our load and with the Tubb2K brake, we were able to tune to a 100 yard 3 shot group of .4" outside to outside. We used our Kestrals to measure the DA, made the calculations with Ballistic FTE on our iPhones using direct DA input and sent the first round. Slightly right of the 20"x20" steel but with perfect elevation.</p><p></p><p>The answer is that we used the 3175 fps number from the Chrony and it was right. The CED was way off. This really is the gold standard of determining whether or not a chrono is correct in my opinion. BTW, I purchased a new Oehler 35 three screen that same week because I got tired of the uncertainty. Although i have to say the the cheap little Chrony has served me well for almost 20 years. </p><p></p><p>In most cases I can remember when my calculated dope was off at 800-1000 yards, it could be tracked to the bullet's BC being substantially less than advertised. I shoot a fair bit of long range tactical events and all the shooters compare and share ballistics. So when a dozen guys tell you a particular bullet is different than published and you're seeing the same thing, you gotta believe it. You also have to be anal about tracking all the relavent data. If you sight in to the north or south and you're shooting east or west (or any variation on this theme), you need to turn on the Coriolis function in your ballistic calculator. At 1000 yards with a 260 Rem, there is .3 MOA of Coriolis shooting east or west. Without this, you could assume your measured speed or your BC was wrong.</p><p></p><p>Hope this helps.</p><p></p><p>[ame=http://youtu.be/NQqjhCCh60Y]Thoroughbred Rifles One Mile Rifle in .300RUM - YouTube[/ame]</p><p></p><p>Dale</p></blockquote><p></p>
[QUOTE="TexasHunter, post: 566112, member: 26082"] Hey Wile, During the load dev and testing of the one mile rifle we built for NTRP, we used a beta and a CED to test loads. With the exact same load, the Beta gave us around 3175 fps and the CED gave us around 3000. Both units were set up at the same bench at the exact same distance. All reloading components were the same as was the load itself. We were developing loads for the 300 RUM using the Hornady 225 grain match. We really needed around 3100 fps to get to the mile with the 225. Needless to say, we were scratching our heads. I called Hornady to confirm the BC of the 225 and they told me .670 G1. My client, Josh Ruby of NTRP had used this bullet extensively in a 300 WinMag and believed it to have a BC more close to .690. So the following weekend we went to his 1780 yard range to test rifle and load. We were getting an SD of 5 from our load and with the Tubb2K brake, we were able to tune to a 100 yard 3 shot group of .4" outside to outside. We used our Kestrals to measure the DA, made the calculations with Ballistic FTE on our iPhones using direct DA input and sent the first round. Slightly right of the 20"x20" steel but with perfect elevation. The answer is that we used the 3175 fps number from the Chrony and it was right. The CED was way off. This really is the gold standard of determining whether or not a chrono is correct in my opinion. BTW, I purchased a new Oehler 35 three screen that same week because I got tired of the uncertainty. Although i have to say the the cheap little Chrony has served me well for almost 20 years. In most cases I can remember when my calculated dope was off at 800-1000 yards, it could be tracked to the bullet's BC being substantially less than advertised. I shoot a fair bit of long range tactical events and all the shooters compare and share ballistics. So when a dozen guys tell you a particular bullet is different than published and you're seeing the same thing, you gotta believe it. You also have to be anal about tracking all the relavent data. If you sight in to the north or south and you're shooting east or west (or any variation on this theme), you need to turn on the Coriolis function in your ballistic calculator. At 1000 yards with a 260 Rem, there is .3 MOA of Coriolis shooting east or west. Without this, you could assume your measured speed or your BC was wrong. Hope this helps. [ame=http://youtu.be/NQqjhCCh60Y]Thoroughbred Rifles One Mile Rifle in .300RUM - YouTube[/ame] Dale [/QUOTE]
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