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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2008 at 22:07
MIKE24 View Drop Down
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I sighted in my 270win. with the primos BDC. My question is, how close is the bullet drop of Winchester 130gr ballistic silvertip compared to the BDC circles? Up to 200yds. should be no problem but how about 300-400yds. My shooting range only goes out to 100yds. so I have no way of testing. Any help would be great. Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2008 at 22:52
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http://www.biggameinfo.com/BalCalc.aspx
 
plug in the info you have on weight velocity balistic coeffecient and this will tell you where it should be at what distance. Then get the info from Nikon on what the marks represent. Testing in the field is the only way to confirm the info.  PS- BDC reticles only work at the highest power.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2008 at 23:14
Tip69 View Drop Down
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Is it possible to figure out where they are on other power levels or can that change from one day to the next?  In other words, if you mostly hunt with it on 4x, can you go to the range and see where the 2nd circle hits at say @200 yds and will it always hit at that spot?  seems to me that it would and that knowing where it hits for just 2 magnifications wouldn't be that hard to remember.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/23/2008 at 09:25
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type it up and tape to scope body or stock
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2008 at 14:28
trigger29 View Drop Down
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X = 180 Y = 90 (X+Pyro)+(Y-Pyro) = ?

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Originally posted by Tip69 Tip69 wrote:

Is it possible to figure out where they are on other power levels or can that change from one day to the next?  In other words, if you mostly hunt with it on 4x, can you go to the range and see where the 2nd circle hits at say @200 yds and will it always hit at that spot?  seems to me that it would and that knowing where it hits for just 2 magnifications wouldn't be that hard to remember.
 
I believe if you know the subtensions or whatever the marks represent, you can plug them in to Exbal and get a figure for where they will hit on a certain power. Zeiss's Rapid-Z calculator on their website is based on Exbal. I have not bought Exbal for myself yet to see how the personal program works, but Zeiss's program has worked very well for me.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2008 at 19:38
3_tens View Drop Down
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Tip if you take a ruler at 100 yds put the Cross hair on zero then read the ruler at all of the marks you can calculate your drop at any range. Sometimes it helps to have someone at the ruler to move a pencil up and down and let them record the drop. You can do this at any power to calculate your ranges at any of your marks.. If on zero and the first mark falls at 3.5 inches then It will be at 7 in. at 200 yds and 10.5 in. at 300yds. Oh yes , if you use a helper to mark the ruler make sure the rifle is unloaded. Some people think this could be safer for the person doing the marking. Loco
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2008 at 21:01
MIKE24 View Drop Down
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Thanks 3_tens, I think that was the answer I was looking for. See if my thinking is correct. I contacted Nikon and the sent me an email with the following measurements for the Nikon BDC reticle. Subtensions (inches at 100 yards)

first circle = 2 inches
second circle = 4.5 inches
third circle = 7 inches
fourth circle = 11 inches                                                                                                           The way I understand 3_tens comment is that crosshairs zeroed at 100yds, then the first circle would be 4in at 200yds. Is that correct? If so what would the second circle be at 300yds? Would it be 9in, 13.5in or 18in at 300yds?                  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2008 at 21:09
Tip69 View Drop Down
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Not sure I asked the right question..... I'm not trying to figure out the inches, but rather what the circles represent at different power levels and IF they stay consistient?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/27/2008 at 14:07
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First, the qualifiers: I’ve never looked at a Nikon BDC reticule. My ballistics program doesn’t have a BC-MV combination that exactly matches Winchester’s numbers for the 130 gr. Silvertip load. I’m assuming a standard barrel length and scope mount height.

At 100 yards, with the Primos set at 9X:

The inside of each circle subtends 2." That is, a 2" target dot fills the circle at 100 yards. So, a 4" dot will fill the circle at 200, and a 6" dot at 300.

The center of the first circle is 2" below the horizontal crosshair. If you shoot a group at 100 yards, using the center of the first circle as an aiming point, that group should be 2" higher than a group shot using the crosshair as the aiming point.

So, the top of the first circle is 1" below the crosshair and the bottom of that circle is 3" below the crosshair.

The center of the second circle is 4.5" below the crosshair.

According to a Winchester catalog, to hit dead on at 200 yards, you need to be 1.8" high at 100. That means that if you sight in 2.1" high at 100 yards, you’ll be on at about 215 and about 2" low at 250.

Sighted in 2.1" high with the crosshair, but using the center of the first circle as an aiming point, you would be 4.1" high at 100, and dead on somewhere around 300.

The center of the second circle would put you 6.6" high at 100 and on at about 380.

Sighted in 6.6" (middle of the second circle in this example) high at 100 yards would put you about 5" high at 75 yards, 10" high at 200, and 5" high at 330. That means that if you put the center of that circle on the bottom of a deer’s chest at any distance from 75 to 330 yards, you should hit between 5" and 10" up on the deer.

Same scope set at 4X:

Sight it in at whatever range you want at whatever power. Shoot a group at 100 yards. Then shoot another group at 100 yards, at 4X, using the top of the first circle as an aiming point. The second group should be 2" to 3" higher than the first group, and the results should be repeatable.

Your results may vary. I’m pretty sure mine would.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/27/2008 at 19:54
3_tens View Drop Down
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The example I was using were just arbitrary numbers for example purpose but the system will give you the ratio's between the marks or circles at any power setting. Then it can be compared to your ballistics for best fit at any known power setting. The system Nikon uses with the circles is to put the average shot into a kill zone at the marked power setting. Measuring the stadias saves a lot of ammunition and time. Again take the measurements with weapon unloaded for safety. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/30/2008 at 21:54
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When adapting ballistic and rangefinding reticles for any particular application it's important tpo understand that with 2nd focal plane reticles such as the BDC u're using the magnification to subtension relationship is inversely proportional, i.e. if the 1st stadia point down is 3 inch per hundred yds. at 9x, then at 4.5x it will be 2x the subtension or 6 IPHY. Now this is assuming the power ring is calibrated correctly for magnification--most are very close, i've found.

 
It's also important to note that the correct unit designation for the measurements (subtensions) is INCH PER HUNDRED YDS. So in the example above the 4.5 IPHY subtension will be 13.5 @ 300. It's not really that important to know that info tho since the units for bullet drop in ballistics programs is in IPHY, and the reticle is IPHY (actually most ballistics programs calc. bullet drop in MOA, but MOA and IPHY are close enuf that it doesn't make that big of a difference until u get to 500+/- yds).
 
Always remember to get the optics catalogs since most of them provide the subtension info of all their reticles. Nikon is great for this.
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