BDC question

[BillTell]

So I'm posting this here because I think the Competition crowd can give me a better answer. I've got a Nikon BDC scope on my inline muzzleloader. While I can't input my exact load into their calculator, I've gotten what they offer as close as possible. It's saying with my gun sighted in at 100yds, my bottom hash will be about 16" low at 200yds. My gun range only goes out to 100yds. So am I right in thinking that if I use that hash at 100yds, it should correspond and be 16" high? I'm planning on going to a competition in June that will have targets out to 200yds +, and want to get a general feel for what each hash will do past 100. So, if I use, say, the 3rd hash down and it's 8" high at 100, using the Nikon info, (assuming it's close to correct) I should be dead on somewhere around 150 with that. Does that make sense to everyone? Or is there something very wrong with my thinking...(I KNOW there is, I just mean pertaining to THIS topic) Thanks in advance.

 

[Chuck R.]

Not necessarily...the only way to know for sure is to shoot at 100 using the hashmarks.

I seriously doubt that a subtense that's 16" low at 200 would be 16" high at 100. Depending on the ballistics it could be only a couple inches high at 100. Check out this chart:

http://www.powerbeltbullets.com/PBB28inchballistics.pdf

For some loads a couple inches high at 100 only result in being 6-7" low at 200.

 

[waktasz]

Try the Strelok app on your phone. It has a tone of scope reticles in it and you can enter your own load data and it will tell you what each BDC line represents. I have found i to be pretty accurate with .223 ammo and my Vortex 1-6 scope.

 

[BillTell]

Yeeeaaaah....my phone still flips open....and doesn't do "app's"...just phone calls.
Thanks Chuck, that actually makes sense, and I want to say I knew that some where back in my thick skull...I'll be at the range tomorrow, and will see what I will see. I just wish my club's range went past 100yds, but, we're close to houses and I'm feeling lucky we've got the 100.

 

[Varminterror]

16” at 200 is 8” at 100. The BDC stadia are no different than any other reticle in that they subtend an angle, which correlates to a scaled height per range. If it’s supposed to subtend 16” at 200yrds, it would be 8IPHY (not quite MOA), so 8” at 100.

 

[BillTell]

Varminterror, you understand I'm trying to figure what 16" LOW at 200 would be, right? I think your telling me I would be 8" low at 100? Also, I'll have to look up "subtend", as I don't know what that means, and I certainly don't know what IPHY stands for, other than I'm thinking the "I" would be inches, but the rest I can't get. I wound up going to the range and sighting in a different black powder gun, and never got to experiment with the BDC reticle, so that will have to wait out this next week's storms at least.

 

[Varminterror]

@BillTell, yes, I completely understand what you are trying to accomplish. But I’m expressing to you - you’ve messed up in your logic, so your hypothesis is wrong.

You asked:

[W]ith my gun sighted in at 100yds, my bottom hash will be about 16" low at 200yds. My gun range only goes out to 100yds. So am I right in thinking that if I use that hash at 100yds, it should correspond and be 16" high?

You are incorrect in expecting 16” high at 100yrds.

If your hash marks “span” or “cover” or “subtend” 16” at 200yrds, then they will only “span” 8” at 100yrds. So if you hold the 200yrd hash on the center of a target at 100yrds, you will NOT be 16” high at 100yrds, you will be 8” high.

IPHY is inches per hundred yards - the adjustments in most scopes aren’t actually 1/4moa, they are 1/4 IPHY, as in 1/4 inch per hundred yards.

 

[BillTell]

Gotcha! I needed a bit of that plain English learnin'