Nielsen 20.2 .22 slugs. BC of .075 isn't striking me as correct.

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Drop is not a great way to calculate BC.

Your shots are landing about 1.35" high at 125 yards. And what you're determining as "high" could very well be swallowed up by what you think your zero distance is versus what it actually is, or by scope height in your program, or elevation or various other ballistic program inputs.

Best way to determine is measuring retained velocity downrange, which is best done by something like a Labradar.

Given all of the above...if you're at high elevation (5-6000+), you could very well be getting a better BC than NSA lists.

In addition, their listed BCs seem to be approximate. Me and a buddy have extensively tested (via Labradar and chrono downrange) the .20/18.9s and they're in the ballpark of 0.085-0.1, depending on speed. And NSA lists them as 0.075 as well.
 
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Franklink said:
Drop is not a great way to calculate BC.

Your shots are landing about 1.35" high at 125 yards. And what you're determining as "high" could very well be swallowed up by what you think your zero distance is versus what it actually is, or by scope height in your program, or elevation or various other ballistic program inputs.

Best way to determine is measuring retained velocity downrange, which is best done by something like a Labradar.

Given all of the above...if you're at high elevation (5-6000+), you could very well be getting a better BC than NSA lists.

In addition, their listed BCs seem to be approximate. Me and a buddy have extensively tested (via Labradar and chrono downrange) the .20/18.9s and they're in the ballpark of 0.085-0.1, depending on speed. And NSA lists them as 0.075 as well.
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at 1211' above sea level scope height is precisely 2.78", zero is exactly 35,
MV 961-966 126y verified by 2 handheld LRF and one Optics mounted, according to chairgun and element shooting at a 6 deg slope at 126 with my MV and the NSA provided .075 i should be at 4.5Mil, I'm hitting 4-4.2 every single shot. Obviously when its gametime shooting i can compensate knowing.. but i'd like a true BC and i can't get my hands on the labradar ATM and don't feel like buying one
 
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That 35 yard zero input is the tricky one. At 960fps, your "zero" should be something like 30 through 45 yards. Plug 30 into the ballistics app versus 45 and you'll see what I mean.

As you're pointing out though, the DOPE acronym is really at play here. (Data On Previous Engagement). Collecting data on impact points at various distances means a "hit" the next time you're shooting at that distance, regardless of the BC numbers. In fact, the DOPE method is the better way to go about this, versus using a ballistics app. When I'm setting up a gun, I follow along with a ballistics app, but the shooting at actual distances is what I create my dope sheet from.
 
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Franklink said:
That 35 yard zero input is the tricky one. At 960fps, your "zero" should be something like 30 through 45 yards. Plug 30 into the ballistics app versus 45 and you'll see what I mean.

As you're pointing out though, the DOPE acronym is really at play here. (Data On Previous Engagement). Collecting data on impact points at various distances means a "hit" the next time you're shooting at that distance, regardless of the BC numbers. In fact, the DOPE method is the better way to go about this, versus using a ballistics app. When I'm setting up a gun, I follow along with a ballistics app, but the shooting at actual distances is what I create my dope sheet from.
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i'm just trying to get a true BC. that's all. For the sake of my specific 'tistic Tolerances. Getting hits out to near 200 is no issue. I'm just trying to ascertain the actual bc because i'm petty like that.
 
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Without a Labradar......

ten shot average at muzzle, then put your chrono downrange, preferably at 50+ yards, and get a ten shot average there. I like 90+ yards for the downrange fps retention for slugs.

Plug those two numbers into any of the numerous calculators and you'll have a pretty good idea of your true BC.

The tighter the spread within each ten shot group, the better the output BC. (Crap in, crap out).

Some shielding for the downrange Chrono is a good idea.

"EasyBC" is one of the better ones that I've seen.
play.google.com

EasyBC - Apps on Google Play

EasyBC is Ballistic Coefficient calculator using the ∆POI, ∆T or ∆V methods.
play.google.com play.google.com
 
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Franklink said:
Without a Labradar......

ten shot average at muzzle, then put your chrono downrange, preferably at 50+ yards, and get a ten shot average there. I like 90+ yards for the downrange fps retention for slugs.

Plug those two numbers into any of the numerous calculators and you'll have a pretty good idea of your true BC.

The tighter the spread within each ten shot group, the better the output BC. (Crap in, crap out).

Some shielding for the downrange Chrono is a good idea.

"EasyBC" is one of the better ones that I've seen.
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Sure. I plan on this. Just wanted to see if anyone else had numbers.. I just wanted to plug them in and see if that comports better with my Chairgun Elite/Element apps.
 
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.075 actually sounds high to me. The type of barrel, with or against the wind, barometric pressure , and velocity all affect the bc calcs.
I don't have numbers for you but can measure them here at 3000 ft elevation if needed. In the 20.2 shooting I've done, they were more wind sensitive and had more drop, than the Jumbo Monster Redesign 25.4s , and those compute for me at the 0.051 area pretty consistently.
I'm currently set up only with an LW poly in 22 though. Possibly could drop a 3 groove TJ in for a quick test. Don't have a 6 or 12 groove handy right now...
Bob
 
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