Author Topic: Trajectory observations  (Read 593 times)

Steelhead

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Trajectory observations
« on: March 13, 2019, 02:19:45 PM »
Had a little time off today and the sun is shining for what seems like the first time this year. Got some shooting in on the backyard range and was working on getting used to my new BSA scope. I also did a side-by-side comparison of NOE 134 gr. BBT flat nose vs. Lee's 113 gr. flat nose gas check (both sized to .309). Accuracy of both was good.  What I found interesting was at 200 yards (the distance I was doing all of my shooting at) my POI was exactly the same with both bullets. I expected the 113 to be a little flatter, but not so. The 134's are shooting around 925 and the 113's around 945. More drag on the 113?


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rsterne

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Re: Trajectory observations
« Reply #1 on: March 13, 2019, 03:49:22 PM »
To really know what is going on, you need two POIs, say at 100 yards and 200 yards.... With that and the muzzle velocity then you can calculate the BCs....

Bob
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Alan

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Re: Trajectory observations
« Reply #2 on: March 13, 2019, 06:00:20 PM »
Or... You bite the bullet and buy a Labradar. Shoot the slug or pellet, push a button, and read the calculated BC.
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Steelhead

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Re: Trajectory observations
« Reply #3 on: March 13, 2019, 07:10:18 PM »
Doggonit, Bob...

You're going to make me pack a steel plate out to the 100 yard tree tomorrow, aren't you? I'll try to make that happen. Casting has added a whole new dimension to my shooting fun, and it's been really rewarding to have great results (and failures) It's fun to have so many different things to feed a big bore and it's an added source of enjoyment to have input in that area.
  • Petaluma, CA
Airforce Texan .308
Benjamin Armada .25 (sold)
Benjamin Discovery .22
Benjamin Prowler .177
FX Streamline .25
JSA Raptor .22

Born Wild Shooting Chair
Air Venturi compressor

rsterne

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Re: Trajectory observations
« Reply #4 on: March 13, 2019, 07:18:05 PM »
A POI comparison between the 2 bullets at 100 yards will tell you which has the superior BC.... Since they are impacting at the same point at 200 yards, if they also impact at the same point at 100 yards, and you know the 113 gr. has a 20 fps advantage at the muzzle, then you will know that the 134 gr. BBT has a better BC, since at those 3 points it has the same trajectory....

If the POI at 100 yards is not the same, then you will need quite accurate measurements of the POI at both distances, from a common aim point, plus the MVs, to calculate the BCs.... ChairGun can do the math for you.... Note, your results will only be as good as your POI measurements....

Bob
  • Coalmont, BC