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Old November 29, 2008, 01:32 PM   #1
hankfan79
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BDC Scope for rifle? How do they work?

Fellow shooters,

I am looking to get a BDC(Bullet Drop Compensator) scope for a rifle. I don't deer hunt much so I am not spending a ton of money for a setup. The max I intend on shooting is 300 yards. I have been surfing the net with no results in sight.

Rifle in question is a 7mm-08
Sighting in at 100 yeards. Longest range that is close to me.

My questions are these:

Does the scope comes with a ballistics guide or some sort?
Every bullet is different, so how do you go about getting one?
Obviously a 30-06 would drop different than a 7mm-08 if I am thinking straight.

I was thinking about getting a Nikon Buckmasters BDC scope(again for the money).

Please do not hammer me with "why buy cheap?" or anything of that nature. I just really want to know how they work according to each caliber.

Thanks guys.
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Old November 29, 2008, 01:50 PM   #2
kyle1974
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my opinion... if the furthest you are honestly planning on shooting is 300 yards with a 7mm-08, you may not even need a ranging reticle.

with a 140 grain bullet sighted 2 inches high at 100 yards, you'll be around 9 inches low at 300 yards.

as for the nikon reticles, they aren't matched to a specific caliber/load combination as far as I know. The only scopes I've seen are pricey (~$1000+) that match the reticle to the specific load. I think the fixed reticles estimate the average drop for standard and magnum calibers. Even the more expensive leupold with the boone and crocket reticle aren't matched to a specific load.
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Old November 29, 2008, 01:55 PM   #3
hankfan79
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9 inch drop? That seems kinda much doesn't it? Then again, I have no freaking clue.

300 yards being absolute max!
This is why I would like a BDC to help me compensate for a 200 yard shot.

If they have no "chart" or "Guide", then whats the point? They wont be accurate will they?

Last edited by hankfan79; November 29, 2008 at 02:02 PM.
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Old November 29, 2008, 02:14 PM   #4
kyle1974
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9" isn't that much really.

do a google search for ballistics, or go to an ammunition website like federal, or similar. They usually have the ballistics for all their loads listed somehow.

federal will produce a short range (500 yards and less) and a long range (to 1,000 yards) chartshowing bullet drop, along with energy and windage plots for their loads.


I've thought the same thing about the generalized bullet drop reference scopes... they're not exactly right unless they're matched to a specific load. I'm not sure if they come with a reference chart or not though....Personally, I'd rather spend the money on a rangefinder and study up on the ballistics.... that way, if you ever get a shot at 400 yards, you won't have to gamble with an inaccurate scope.
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Old November 29, 2008, 02:45 PM   #5
nate45
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Bullet Drop Compensator (BDC)

BDCs on scopes have an elevation knob specifically matched to your cartridge and load. You use them in coordination with a range finder. The elevation dial will be marked 100 yd or m, 200 yd or m, etc and you turn the dial to the appropriate distance.

A ballistic reticle, such as the Burris Ballistic Plex, has a certain amount of drop preset into the hash marks and its up to you to sight in to match the built in drop. This fully explains it Ballistic Plex™ Reticle . Some companies such as Leupold provide custom reticles where the range hash marks precisely match your selected cartridge and load.

If learn to use a ballistic reticle and carefully follow the instructions they could work well for you, especially at the relatively close ranges you are talking about.
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Old November 29, 2008, 03:05 PM   #6
JohnKSa
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Hornady sells a Light Magnum version of the 7mm08 which can be used in bolt rifles (no semi-autos). It cranks out a 139gr bullet at 3000fps.

Zeroed 2.0" high at 100 yards it will be 2.2" high at 130 yards (highest point on the trajectory), dead on at 220yards and 5.6" low at 300.
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Old November 29, 2008, 03:06 PM   #7
hankfan79
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Check this link out for the Burris scopes:

http://www.burrisoptics.com/pdf/BPlxlabl.pdf

Its saying that for a 7mm-08 with a 140 gr bullet, the strajectory(zeroed @ 100) is 0 @ 200yd, +1 @ 300 and 0 @ 400??

Does that mean the bullet goes straight, then up, then down again??
What the heck?
Man, I dont understand this crap!
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Old November 29, 2008, 03:10 PM   #8
nate45
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Quote:
Its saying that for a 7mm-08 with a 140 gr bullet, the strajectory(zeroed @ 100) is 0 @ 200yd, +1 @ 300 and 0 @ 400??
What those figures correspond to is + or - the drop that is built into the reticle.

Read this http://www.burrisoptics.com/pdf/BALLPLEX.pdf and you will understand what I mean.

In the example you sited the 0 at 200 yards means that the trajectory of that load corresponds exactly with the drop built into their reticle. The + 1 at 300 means that load is one inch higher at 300 yards than the drop built into the reticle, etc.
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Last edited by nate45; November 29, 2008 at 03:16 PM.
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Old November 29, 2008, 05:31 PM   #9
globemaster3
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Hank, I own one of the Nikons with the BDC. First, the scope is not matched up against a particular cartridge from what I've read in the owner's manual. As you adjust the magnification, your stadia circles below the primary crosshair will change, ie, they won't be the same distance in relation to your target. What it will do for you is at a given magnification, you can test it at different ranges and use the circles to help your holdover. ie, at 9 power, with a 100 yard zero, the first circle should be close at 200 yds, but it might be the top of the circle or the bottom. The same for the second circle at 300 yds.

As soon as I finish getting settled in to this new house, this scope is going on a .308 and going to the range so I can figure it out. I'll be happy to let you know what I discover. It will be a couple more weeks before I get out there, though.
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Old November 29, 2008, 07:35 PM   #10
JohnKSa
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You can get BDC scopes made for very common calibers (e.g. 308, .223, etc.). Those may consist of a special reticles with marks for holdover/holdunder or they may consist of adjustments on the scope that you set to the applicable range and then shoot directly to the crosshairs/reticle. If you are using a less common caliber you can either try to get a custom reticle or adjustment cams or puchase a scope with a lot of reticle elevations markings and learn which markings correspond to various ranges with your particular gun/ammo combination.
Quote:
Does that mean the bullet goes straight, then up, then down again??
Go look at your rifle. You'll see that the bore of your rifle is below your scope.

That means that the bullet starts out BELOW the line of sight through the scope.

The gun is sighted so that the bullet describes an arc on the way to the target.

Initially the bullet rises to the line of sight (usually at about 25 yards) then it continues to rise above the line of sight until gravity brings it back down. It will reach the apex somewhere about 60% of the way to the target. Then gravity will pull it downward. When it crosses the line on the downward end of the arc, that is the range for which the rifle is zeroed.

Here's a handy ballistic calculator.

http://www.handloads.com/calc/

The markings on the chart you're talking about do not correspond directly to trajectory. If you zoom in there's an explanation in small letters next to each diagram. What they're saying is that if you use the specified reticle marking at the specified range the bullet will hit either right on (0) or it will be high or low by the specified number of inches.
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