What's a BDC??

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Smokey Joe

New member
Sorry to sound like a newbie; I guess we all have something to learn now & again. It's my turn.

The term "Bullet Drop Compensating," with reference to a rifle 'scope, is a new one on me. What is it for, why is it good or bad, do I want to pay extra for it??

I'm well aware that a bullet begins to drop, right out of the muzzle, when fired. You don't have to explain trajectory.

But what do they build into a 'scope for this???
 
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root

New member
essentially it lets you adjust the scope for the individual caliber's trajectory, if you know your target is 300 yards out, click in 300 yards and you simply hold your crosshairs on target instead of estimating how high to aim to adjust for bullet drop.

is it useful? well, only at known ranges (read -good- rangefinder)
worth extra? maybe.

depends on environment, a lot of people are just as happy with a mil-dot reticle.
 
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Capt. Charlie

Moderator Emeritus
Actually, a BDC compensates for the angle you're shooting at, i.e., what angle uphill or downhill. If, for example, you're shooting from a hilltop downward at an angle of 30 degrees, the bullet will drop less at a given range than it would if you were shooting from and to a flat surface (parallel to the earth). A BDC calculates that difference.
 
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Smokey Joe

New member
OK....

Now we've got two completely different explanations. Which one is the correct one???

BTW, Krezyhorse, I'm sure you're right, it IS a gimmick. (Whichever it is.) But while most are just unnecessary bells & whistles, some gimmicks are useful.
 
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Shooter 973

New member
BDC....

I have a Colt BDC 4 power scope on my AR-15A2 that is a factory original.
It is calibrated to the GI 55 gr load. and it is dead on! :D I've made hits out to 500 yards with it by just setting it to the 500 yard mark and holding dead on. Sure makes it easy to do those longer shots for me. It works better that a MIL-dot scope for me. I have a couple of MIL-dot scopes, on a 30-06 and one on a 308 and they are good but the Colt scope is much easier to to be sure. I like both types but the BDC is sure fun. :)
 
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Kreyzhorse

New member
BTW, Krezyhorse, I'm sure you're right, it IS a gimmick. (Whichever it is.) But while most are just unnecessary bells & whistles, some gimmicks are useful.
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Smokey Joe - Well said. There are certainly gimmicks that, gimmick or not, might be useful.

The BDC might serve better during long distance shooting than during the a hunt, in my opinion anyway.
 
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wogpotter

New member
BDC's are frequently callibrated for a specific load/BC/velocity.
IF you're using that load then they will work pretty well.
But, if you change any of the conditions the BDC was designed for then it will be "off" with the error increasing with range.

It depends on how well you judge distance & know the trajectory of your load. Can it be "better" than you? Maybe.

Having said that I have a scope that has a "short" (300Yd). setting, and a "long" (500Yd) setting.
I tried this out after zeroing as per the instructions and I was pleasantly surprised to find it was dead-on at 500yds.
 
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MTMilitiaman

New member
I'm sure some will disagree, but I think a BDC is a gimmick.
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^ Has never used an RCO (ACOG). ^

BDCs are not a gimmick. Or at least, they don't have to be. If all you do is travel down to the 100 yard range that requires slowfire and regulates your shooting positions and all that BS, then yeah, a BDC might not be all that useful.

But if you're shooting targets at unknown distances at ranges that may require compensation and you have to do it quickly, a BDC is invaluable. Set up properly, such as on the RCO, it allows you to estimate range and compensate for drop almost instantly in a manner that is simple and easy to do under pressure. When you see people who are relatively new to rifles making consistent hits at 500+ yards from field positions, on the clock, with a mass produced rifle and mass produced ammunition, you are left with little room to doubt the utility of a BDC.

Likewise, if you're proned out on your drag bag behind a rifle with your eye to the scope calculating mils on a target 1000+ yards away, having range marked on your elevation dial helps immensely; "okay so divide by...now multiply by 100...so that's about 1090 yards...turn dial to 11...focus on fundamentals..." compared to the alternative, without the BDC--"okay so divide by...now multiply by 100...so that's about 1090 yards...bullet drops about 29 MOA...we're at 600 yards now which is 11.5 MOA...so that makes plus 18.5...multiplied by four gives me...74 clicks...1,2,3,4,5,6,7...65,66,67,68...wait was that one click or two...is it 68 or 69...DOH!"
 
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match308

New member
root is correct. BDC is a general calculation based on a bullets trajectory related to a level plane. Useful for the shooter that engages targets at known distances and needs to be able to break the shot without dope adjustment to the scope.
 
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Capt. Charlie

Moderator Emeritus
root is correct. BDC is a general calculation based on a bullets trajectory related to a level plane. (emphasis: mine)
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OK, perhaps I'm the one that's somewhat cornfused here. I distinctly remember a discussion here a while back about an article in SWAT Magazine. It centered on a gizmo used by snipers to compensate for different trajectories encountered when shooting at different angles downhill or uphill.

I tried searching the forums for that thread using "BDC" and "bullet drop compensator" and got zip :confused:. That kinda suggests that I got a BDC mixed up with some other critter :eek:.

Does someone want to enlighten me here?
 
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kkb

New member
I tried searching the forums for that thread using "BDC" and "bullet drop compensator" and got zip . That kinda suggests that I got a BDC mixed up with some other critter .

Does someone want to enlighten me here?
Click to expand...

Might it have been a rangefinder discussion? I know there are several rangefinders that compensate for incline, e.g. Leupold's RXB-IV.

Perhaps the Barrett BORS?
 
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wogpotter

New member
I think what you are thinking of is a gadget called an "angle cosine indicator"
It attaches to your scope externally and shows the upward/downward angle to target.
 
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Capt. Charlie

Moderator Emeritus
I think what you are thinking of is a gadget called an "angle cosine indicator"
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BINGO! I knew I wasn't crazy! :D Here's the thread I was thinking about, but given that I've never had cause to use one, it sorta slipped back into the dim, cobweb ridden recesses of my mind. Thanks for the refresher, wogpotter :).
 
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kennybs plbg

New member
I purchased a Bushnell Scopechief in 75 with a BDC (2.5x 8)that was one of the best scopes I've ever owned. It was mounted on a 270win that was my favorite chuck rifle for over 20 years. If used correctly and set up properly within its limitations it was a tack driver out to 300 yards, beyond that it was useless. Unfortunitly after 21 years I sent it back to bushnell for a 10 cent part and they sent me some junk Bausch and Lomb replacement.

kenny b
 
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Zak Smith

New member
This covers BDCs and their advantages vs. disadvantages.

A100_1910_img.jpg

article | Practical Long-Range Rifle Shooting, Part II - Optics
 
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wogpotter

New member
Just a little anecdotal information on BDC's.

I took the BDC equipped Fero scope to a range that runs from 100~600 yds today & here is what I found out.
Zeroed at 100yds (& set there also) the BDC was accurate out to about 400yds. After that it started shooting low at 500 & 600 yds.

I reset the zero at 400yds and went back to the 100~600yd points setting the distance in use on the BDC. It was accurate at all ranges.

Now for the kicker. The BDC is set up for a 147 Gr. Nato Std 30 cal projectile fired at 2850 FPS (nominal).

I was using handloaded 165 Gr bullets at 2650 FPS measured.

I guess they do work well after all the thoeries have been debated.:)
 
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