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 October 7, 2021, 06:38 AM #1 tpcollins Senior Member   Join Date: February 18, 2009 Location: SE Michigan Posts: 557 Question for the MOA aficionados I realize this isn’t a firearm example but the answer should work the same way. I have a trajectory that has a 10.17” drop at 50 yards with a 30 yard zero. If I divide 10.17 by .5 (50 yards / 100 yards) = 20.3 x 1.047 = 21.3 MOA drop . . . yeah or nay? I assume holdover equals drop but “clicks up” is different. Thanks. . __________________ What direction did that last shot at Kennedy come from? Last edited by tpcollins; October 7, 2021 at 06:44 AM.
 October 7, 2021, 07:07 AM #2 tpcollins Senior Member   Join Date: February 18, 2009 Location: SE Michigan Posts: 557 Actually I think I should divide by 1.047, not multiply . . . = 20.3 x 1.047 = 21.3 MOA drop versus 20.3 / 1.047 = 19.39 MOA __________________ What direction did that last shot at Kennedy come from?
 October 7, 2021, 12:59 PM #3 HiBC Senior Member   Join Date: November 13, 2006 Posts: 7,703 It may involve more variables than you are considering. If you are involved in shooting a firearm,you must consider the line of your sights is offset from the line of the bore. If you are just working out a geometry problem,make a reasonably nice drawing, Use a straight edge. X-Y grid paper may help. Identify the triangles and team up with Pythagoras.Its mostly basic trig. If you go to the Hornady Bullet Website, you can access a free ballistic software to play with. Its an easy to use,good tool
 October 7, 2021, 04:13 PM #5 Rhodester Member   Join Date: January 30, 2019 Location: North Canton, Ohio Posts: 19 My head hurts.
 October 7, 2021, 05:01 PM #6 stinkeypete Senior Member   Join Date: July 22, 2010 Location: Madison, Wisconsin Posts: 956 Well, my Honors Geometry students would all be able to do that calculation. It’s basic unit conversion and triangle trig, freshman/sophomore level math. __________________ I hunt, shoot bullseye, plink, reload, and tinker with firearms. I have hung out with the Cowboy Action fellas. I have no interest in carrying firearms in urban areas.
 October 7, 2021, 07:14 PM #7 HiBC Senior Member   Join Date: November 13, 2006 Posts: 7,703 In shop math language, you have to convert all the numbers to the same units of measure (inches or feet or cubits,doesn't matter. But you may need your range to the target in inches if you measure your sight radius in inches,etc.)
October 7, 2021, 09:51 PM   #8
TXAZ
Senior Member

Join Date: September 5, 2010
Location: McMurdo Sound Texas
Posts: 4,313
Quote:
 Originally Posted by tpcollins I realize this isn’t a firearm example but the answer should work the same way. I have a trajectory that has a 10.17” drop at 50 yards with a 30 yard zero. If I divide 10.17 by .5 (50 yards / 100 yards) = 20.3 x 1.047 = 21.3 MOA drop . . . yeah or nay? I assume holdover equals drop but “clicks up” is different. Thanks. .
Sounds like a high end slingshot at 660 ft/ sec…
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 October 8, 2021, 11:53 AM #9 tpcollins Senior Member   Join Date: February 18, 2009 Location: SE Michigan Posts: 557 I got figured out. My 2nd post was correct. __________________ What direction did that last shot at Kennedy come from?
October 9, 2021, 01:07 AM   #10
Pathfinder45
Senior Member

Join Date: January 7, 2008
Posts: 3,083
Quote:
 Sounds like a high end slingshot at 660 ft/ sec…
Not even that good....more like the slingshot I made when I was 8 using a forked stick and rubber straps cut from an old inner tube.

 October 9, 2021, 07:04 AM #11 std7mag Senior Member   Join Date: June 23, 2013 Location: Central Taxylvania.. Posts: 3,420 Just shoot the freak'n thing already!!! Took longer to ask the question, and get a response, than to shoot it (whatever it is) and get meaningful field data. Otherwise known as dope. I never got past first year algebra. __________________ When our own government declares itself as "tyrannical", where does that leave us??!! "Januarary 6th insurrection". Funny, I didn't see a single piece of rope...
 October 9, 2021, 01:52 PM #12 JohnKSa Staff   Join Date: February 12, 2001 Location: DFW Area Posts: 24,023 The first thing you need to know is what 1 MOA is at the distance in question. Here's a really simple formula for calculating the value of 1 MOA in inches at any distance given in yards. Distance (yards) / 95.5 = MOA (inches) That will give you an answer with an error of less than 0.01% 50 / 95.5 is about 0.524 which means that the value of 1 MOA in inches, at 50 yards is about 0.524" You want to know what 10.17" at 50 yards works out to in MOA. 10.17" /0.524" is about 19.4 MOA. __________________ Do you know about the TEXAS State Rifle Association?
 October 11, 2021, 06:50 PM #13 hounddawg Senior Member   Join Date: March 1, 2009 Posts: 4,060 when I can hold and shoot down to .047 inch accuracy I will sweat it, until then........ __________________ “How do I get to the next level?” Well, you get to the next level by being the first one on the range and the last one to leave.” – Jerry Miculek
 October 12, 2021, 12:13 AM #14 JohnKSa Staff   Join Date: February 12, 2001 Location: DFW Area Posts: 24,023 In this case, let's say we approximate 1MOA as 0.5" at 50 yards, instead of using its actual value of 0.524" Then we would calculate that 10.17" was 20.3 MOA instead of the correct value of 19.4 MOA. If we dialed the 20.3 MOA value into the scope, we would be off by 4 clicks in a scope with 1/4 MOA clicks--half an inch at 50 yards and an inch at 100 yards. Not a huge error, but definitely a lot more than 0.047". __________________ Do you know about the TEXAS State Rifle Association?
 October 12, 2021, 04:39 AM #15 hounddawg Senior Member   Join Date: March 1, 2009 Posts: 4,060 bet if you do this test you will find your scope tracking off by more than .047 inches also https://www.youtube.com/watch?v=12Wf0Cuwwi8 to quote a previous poster Just shoot the freak'n thing already!!! __________________ “How do I get to the next level?” Well, you get to the next level by being the first one on the range and the last one to leave.” – Jerry Miculek
 October 12, 2021, 11:55 AM #16 Bart B. Senior Member   Join Date: February 15, 2009 Posts: 8,706 https://www.nssf.org/shooting/minute-angle-moa/ Most exact number I've seen is this one to a hundred places... 1.04719753642832854694747069666400334739860873986429830552235157457471965151538005004775737357536725837... .... inches per hundred yards. However, most bullseye targets in the USA have rings in inch spaced sizes. They are set at ranges measured in yards. Therefore, using MOA values in inches simplifies many issues. Aperture rear sights made in the USA normally have 40 tpi adjustment screws. With 12 clicks per turn, the standard 30 inch sight radius from the front sight enables 4 clicks to move impact exactly 1 inch per hundred yards. Last edited by Bart B.; October 12, 2021 at 04:14 PM.
October 12, 2021, 11:40 PM   #17
JohnKSa
Staff

Join Date: February 12, 2001
Location: DFW Area
Posts: 24,023
Quote:
 Therefore, using MOA values in inches simplifies many issues.
I don't believe anyone is advocating anything else.

For those who are, 1 MOA at 100m is about 2.909cm--or one can round that to 3cm.

Interestingly enough, approximating 1MOA as 3cm at 100m is only in error by about 3% as opposed to the roughly 5% error generated by approximating 1MOA as 1" at 100yds.
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