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Posted: 11/21/2015 11:54:30 PM EDT
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Is there a chart or graph somewhere?
Looking for 75 and 77 gr from 16 and 18" barrels. So I have the 16s zeroed at 50 yards and 18s at 100 yards |
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Quoted:
Is there a chart or graph somewhere? Looking for 75 and 77 gr from 16 and 18" barrels. So I have the 16s zeroed at 50 yards and 18s at 100 yards I've searched for one couple weeks back with no luck However, there are calculators like the one on Hornady's website you can use. With a Mk262 and other 77gr OTM 5.56 ammo, at 2650fps, zeroed at 200yards, BC of 0.35, the drop is approximately 9.7" low at 300yards. Zeroing at 200yards has always been my preferred method for 5.56 guns. I can't easily access to a 300-600yard range to confirm, but at 100yards the calculator is pretty accurate with its data telling me it will be 2" high, which in reality it is 1.8" |
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I zero all my 5.56/.223 ARs at 200. 50/200 zero is good regardless of barrel length. Especially for M193 or similar 55gr loads.
The Strelok app for droid or IOS is the best out for ballistics. Before Strelok, I used this calculator Each load will have different velocities and each barrel also. If you can get your loads chrono'd it will help. Here are my heavy load velocities from a 16" McGowan, 1:8 twist: 75gr Hornady hand loads were chrono'd at 2550 fps. .3 high at 100, 1.7" high at 100, 0 at 200 and 9.5" low at 300. 77gr SMK's hand loads were chrono'd at 2460 fps. .9" high at 100, 2" high at 100, 0 at 200 and 10.5" low at 300. |
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I've been shooting the AR15 only since about June or July and had a lot of trouble trying to find ballistic coefficients and muzzle velocities online. It perplexed me (as I was ignorant) that various sources gave different values for BC and MV.
Then I got schooled and learned that if I wanted accurate (or, as accurate as possible) ballistic charts I needed to do the following two things: 1) Get a chronograph and measure at least a 5 shot string of the exact ammunition down to the lot number that I intended to model and from the rifle I intended to use. 2) Buy the Seirra Infinity 7 exterior ballistics program (about $35) and take advantage of the update available for that program which contains as comprehensive a library of BCs that I've seen anywhere (both Sierra and other bullet manufacturer's BCs). Infinity 7 allows the input of atmospherics and elevation and wind speeds too. So, you can generate an accurate plot just before you head to the range. So far, at least, the accuracy of the plots out to 300m has been remarkable...probably within 10% at any range I've fired. I know it seems like a lot of effort. But the Magnetospeed Sporter I bought was only $189 and the softward only $35. So, for about $200 I'm about as accurate as I know how to be in my plots and holdovers at range. But what does one get for such expenditures of money and time. Well, over time I became aware that using just those tools and an occasional trip to the range to see how my rifles grouped and stabilized certain ammunition I could eliminate some ammunition from the list of those in which I had an interest as "duty loads". As the range data tended to agree so closely to my ballistic data it meant that I could greatly diminish the number of expensive range visits I made without losing much confidence in my ammunition choices. I think I've saved money by buying the software and the inexpensive chrono without any decrease in the fidelity of my judgements. Best, LF |
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