Question about bullet drop/aiming with .223/5.56.

[larry0071]

I know, this seems almost a stupid thing to ask, but the other day I was shooting with my BIL and our two AR's are side by side. I noticed that he has the non removable carry handle with the scope mounted over top. Mine has the removable carry handle and my scope is mounted much lower to the barrel center line.

So.... I understand that bullet rise is not due to a bullet coming out of a barrel and magically going up in elevation, but rather is from the fact that the sights/optics are at some elevation higher than the barrel CL and this causes the barrel to be pointed upwards in relation to the optics causing the bullet to rise over time until the distance that your bullet rise and optical CL meet. That point would be the adjusted ZERO.

Here is what gets me, my gun has a lower sight CL comapered to the barrel CL, my BIL's gun has a higher sight CL compared to his barrel CL. So his bullet at any given ZERO DISTANCE will have the bullet traveling up at a sharper angle to meet his scope zero compared to mine at the same distance.

Since the energy of the bullet at say 100 yards is still sufficiant to maintain more upward travel before gravity takes over and stops upward travel, his bullet is off more than mine (both before and after) at the targetted distances OTHER THAN the adjusted zero.

Since you can easily get a reasonable measurement of the barrelCL to optical CL, is there a way to plot the rise/drop compensation for each of our guns? I assume a furmula has been designed to allow the various weapon builds to be simply mathmatically computed to tell the shooter approx how high or low the bullet is from the sighted point based on the ballistic power of the bullet (overpowering gravity on the upward part of the travel) or low as you reach out into the 200-600 yard area and must lob the bullet at your target.

I hope I am looking at this correctly, I do not think that bullets leave a straight barrel and actually gain elevation.... I feel that bullets leave a straight barrel that is pointed slightly upwards to triangulate with the optical alignment at some distance and this simulates a rise in bullet compared to a theoretically horizontal barrel.

Take me to school..... If I am an idiot, I accept it.

Larry

[larry0071]

Not sure if I actually asked the question correctly, so let me be more clear.

This picture shows things as I suspect they are.... call it Larry's World if you will.

http://i409.photobucket.com/albums/pp174/larry0071/Junk%20Repository/BulletRise.jpg

Now, depending on the way a person mounts a RDS or scope, he can effect the spread between the two horizontal planes.

As the spread gets larger, the angle of rise applied to the barrel increases.

As this angle increases, the amount that your bullet is off of the zero point at any distance other than zero also increases.

Since I am not the smartest guy in the world, I have no clue how to decide at what distance it is that my bullet will stop rising and decide to instead begin dropping. If and when this turn from up travel to down travel is observed, would the spread effect this and influence the drop velocity as well as increase the rise velocity?

Where I see the biggest issue, is if I assume that the bullet has enough energy to rise out to say.... 150 yards. But I sight in and zero out at 75 yards. Now lets say that my Brother In Law also zeros at the same 75 yards.... but his spread is massively larger than mine with his scope mounted on top of the carry handle. At 150 yards, since my angle of rise is much less severe, my rifle shoots only some distance high... lets say 4 inches. But his, with the high spread and larger angle of barrel rise to meet his 75 yard zero... his bullet at that same 150 yards might be 9 inches high.

Since in my fantasy world the bullet is going to stop rising at 150 yards, we see that his bullet is setting 5" higher than mine by my fantasy theory. So from here on out there is a fudge factor that prevents he and I from being able to follow the same set of rules to aim out to 400 yards.

Also your distances shorter than your zero distance are off by more on his gun than mine, as my bullet started closer to the center line of the site so has less upward angle on it.

I am wanting to find a math formula that I could use to make a cheat sheet for each AR I have and also his that shows approx how far off the bullet will be and take into account that the optical vs barrel origins are not both at the same elevation.

I hope I did not screw that up....

Larry

[JSantoro]

What I'm getting out of your overall question is that you're trying to discover the max-ord realtive to you and your BIL's rifles.

Have you plugged in your known data to any of the free ballistic calculators out there? They can tell you at what meter - yard - and maybe even foot - line your round hits max ord and begins to fall.

Try this if you have a lot of raw data to punch in: http://www.jbmballistics.com/

This one is simpler, but still pretty good: http://www.robsoft.nu/ballistik_en/ballistik.asp?MainID=3&Show=1&strMedelande=The%20velocity%20must%20be%20between%20300%20and%204500%20fps.%20&Hastighet=&Kulvikt=&BallCoeff=&Hojd=&Temp1=&SiktesHojd=&Maxavstand=&Utokning=&InskjutningsAvstand=

Something to bear in mind, is that gravity is a constant, so once your bullet hits max-ord, or the apogee of the arc it is describing, gravity makes it fall at the same rate it makes everything fall (barring atmospheric and surface area variations). Point being, pretty much any bullet is going to fall at the same rate, while the angle of your barrel in relation to your sight LOS will dictate HOW SOON it will begin to fall.

[Icculus]

Your question hurts my fragile brain.

I don't have the answer but definitely curious so replying mainly so I'm subscribed to this thread and will see the answer when it does show up. That and I just like looking at your avatar;)

[d90king]

I dont mean to overly simplify, but if I am reading your question properly, it is simply knowing your zeroes. All you should need to know is what distance the rifle you are shooting is zeroed from. Each distance equals different POA and POI.

Memorize the charts for zeroes from 25-100 yds and that should help... Bullet weight can also make a slight difference also..

Look for the thread on "what distance do you zero your Aimpoint", if memory serves me some members posted the drop numbers...

Most guys use a 50yd zero for inside 200yds.

[RojasTKD]

I know, this seems almost a stupid thing to ask, but the other day I was shooting with my BIL and our two AR's are side by side. I noticed that he has the non removable carry handle with the scope mounted over top. Mine has the removable carry handle and my scope is mounted much lower to the barrel center line.

So.... I understand that bullet rise is not due to a bullet coming out of a barrel and magically going up in elevation, but rather is from the fact that the sights/optics are at some elevation higher than the barrel CL and this causes the barrel to be pointed upwards in relation to the optics causing the bullet to rise over time until the distance that your bullet rise and optical CL meet. That point would be the adjusted ZERO.

Here is what gets me, my gun has a lower sight CL comapered to the barrel CL, my BIL's gun has a higher sight CL compared to his barrel CL. So his bullet at any given ZERO DISTANCE will have the bullet traveling up at a sharper angle to meet his scope zero compared to mine at the same distance.

Since the energy of the bullet at say 100 yards is still sufficiant to maintain more upward travel before gravity takes over and stops upward travel, his bullet is off more than mine (both before and after) at the targetted distances OTHER THAN the adjusted zero.

Since you can easily get a reasonable measurement of the barrelCL to optical CL, is there a way to plot the rise/drop compensation for each of our guns? I assume a furmula has been designed to allow the various weapon builds to be simply mathmatically computed to tell the shooter approx how high or low the bullet is from the sighted point based on the ballistic power of the bullet (overpowering gravity on the upward part of the travel) or low as you reach out into the 200-600 yard area and must lob the bullet at your target.

I hope I am looking at this correctly, I do not think that bullets leave a straight barrel and actually gain elevation.... I feel that bullets leave a straight barrel that is pointed slightly upwards to triangulate with the optical alignment at some distance and this simulates a rise in bullet compared to a theoretically horizontal barrel.

Take me to school..... If I am an idiot, I accept it.

Larry

Think this thread and links covers it well.

https://www.m4carbine.net/showthread.php?t=31201

[d90king]

Think this thread and links cover it well.

https://www.m4carbine.net/showthread.php?t=31201

What does that thread have to do with zeroes or bullet drop?

[Jay Cunningham]

Larry,

You should check in with The_War_Wagon, pah151 and eagle5 and ask them what they discovered concerning zero, offsets and holdovers when we were out shooting.

https://www.m4carbine.net/group.php?groupid=2

[Molon]

H.O.S.A.B. = height of sights above bore

http://www.box.net/shared/static/lna7h04qxy.jpg

[larry0071]

Think this thread and links cover it well.

https://www.m4carbine.net/showthread.php?t=31201


Rojas,

That link is about gun trusts. Can you share with me the link you intended to show me please?

[larry0071]

H.O.S.A.B. = height of sights above bore

http://www.box.net/shared/static/lna7h04qxy.jpg

Molon,

Your reading my mind. That is exactly what I am looking for, but I was hoping to find a furmula or something.

Someone early on mentioned some software or something. Where can I find it? I also have a Windows Mobile 5 cell phone, so there could may well be something that will work within the Win Mobile world?

Larry

[d90king]

I believe this is what you are looking for... Near the bottom of the page.
http://m4carbine.net/showthread.php?t=34671&page=3