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Old 08-05-2017, 08:56 PM
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Default Somebody please explain this bullet drop.

M&P 15-22 with 2moa Holosun red dot and roughly a 25 yard zero. Federal 36gr copper plated hollow points. Every ballistic table I've checked, including Federal's own, says on at 25, 1" high at 50, back on around 75, and about 3" low at 100. My results are way different. Check the attached pic. Point of aim was red dot at every distance. On at 25 yards, on at 40, 3.5" low at 60, 5" low at 80, 8" low at 100.

How can the ballistics say 1" high at 50yards and I be 3.5" low at 60? I do realize red dots are not magnified scopes, but I'm still surprised by the difference.
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Old 08-05-2017, 09:10 PM
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Here is a ballistic calculator:
Handloads.Com Ballistic Calculator
Be sure and fill in all the blanks, INCLUCING THE HEIGHT OF THE SIGHT AXIS ABOVE THE BORE AXIS.
The increased height on imitation military rifles do not match regular tables.
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Old 08-05-2017, 09:24 PM
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Quote:
Originally Posted by OKFC05 View Post
Here is a ballistic calculator:
Handloads.Com Ballistic Calculator
Be sure and fill in all the blanks, INCLUCING THE HEIGHT OF THE SIGHT AXIS ABOVE THE BORE AXIS.
The increased height on imitation military rifles do not match regular tables.
Just checked that one too. Same outputs.
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Old 08-05-2017, 09:34 PM
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Originally Posted by emsg19 View Post
Just checked that one too. Same outputs.
If you list your inputs, I can check for you. I suspect part of the problem might be that your "roughly 25yd zero" is more like 30 yd and you are sighted lower than you assumed.
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Old 08-05-2017, 09:42 PM
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Common trajectory charts just don't work with an AR-type rifle because the height of the sight line is so far above the bore axis. Most charts are figured with a sight height above bore axis of 1.5", while with an AR it's more like 2.5 to 3".
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Old 08-05-2017, 10:06 PM
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Here's what I got using the Federal calculator, your ammunition, and an optic 2.5" above center of bore. Zero at 25 yards / 5 yard increments / 100 yard distance:

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Old 08-05-2017, 11:00 PM
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Quote:
Originally Posted by bamashooter View Post
Here's what I got using the Federal calculator, your ammunition, and an optic 2.5" above center of bore. Zero at 25 yards / 5 yard increments / 100 yard distance:

That's what I got too. From multiple calculators. I even changed the temp and altitude to be more accurate.
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Old 08-05-2017, 11:15 PM
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Is it possible that I'm not getting the full velocity because the 15-22 is basically an all polymer rifle compared to a more traditional 10/22 type?
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Old 08-05-2017, 11:27 PM
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How high the scope rings are matter a lot.
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Old 08-05-2017, 11:43 PM
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Default No, polymer makes no difference....

The numbers make sense to me. Remember that a bullet starts to drop as soon as it leaves the barrel, which is why it is actually pointed up a bit. At close range, the drop won't count for much because of the short time the bullet it in the air. Also, a bullet crosses the line of sight, TWICE. Once going up as a result of the barrel being pointed slightly upward. And when the bullet stops climbing and drops, it crosses the sight line again. Any distance after that point will result in drop below the line of sight. I've seen some loads that are so parabolic as to drop 24" at 100 yards.

AND as has already been said, the parallax on an AR 15 type is 2.5 " above the barrel centerline as opposed to a rifle with a ramp sight mounted on top of the barrel that are .5" above the barrel center.

Whatever distance you set your zero for, subtracting or adding distance increases the deviation from the POA at the line of sight. A FLAT shooting gun like a 5.56 AR at 3000 fps is not as affected by this as a typical .22 round going 1500 fps will be. Also, note how the ballistic coefficient of the bullet affects how a bullet retains velocity. A long spitzer vs a RN bullet will keep velocity longer, and drop less due to the amount of time in flight.

When I load my 30-06 with bullets going 1700 fps as opposed to 2800 fps, there is a big difference in the amount of drop, so LOAD and bullet velocity counts a great deal.
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Old 08-06-2017, 12:59 AM
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Whether it's one of my 5.56s, 10/22, or my 15-22, I'm always very close to assorted calculators with my range time (using a bench). I have the Holosun HS503C on my latest AR upper. It has the 2 moa dot and 65 moa circle. With a 1/2" riser it's perhaps 1.5mm low of being perfect absolute co-witness. Very, very close to 2.5" and aligns well enough with my MBUS. If you have the same optic with the factory mount, the glass sits a bit high as compared to other red dots.
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Old 08-06-2017, 08:25 AM
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Another consideration -- a 2 MOA dot is a pretty sorry device to shoot with at longer ranges. At 100 yards the best you can hope for is being within 2" of where you think you're aiming. Your potential aiming error at 25 is 1/2" -- try plugging in those figures with the actual zero 1/2" low at 25 and see what you get
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Old 08-06-2017, 03:18 PM
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Thanks for all the input. Someone on another forum also mentioned barrel length being a major factor. Too many variables for a calculator. I'm just going to dial in the zero I want with the ammo I want it zeroed for, then make my own notes at different distances and different ammo to learn the holds.
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Old 08-06-2017, 06:13 PM
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Sounds about right.

You're an inch low at 25...add in sight height above
bore, plus drop at 100 yards from table, and you're
only an inch or so off...
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Old 08-06-2017, 07:31 PM
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Default Velocity.....

Quote:
Originally Posted by emsg19 View Post
Thanks for all the input. Someone on another forum also mentioned barrel length being a major factor. Too many variables for a calculator. I'm just going to dial in the zero I want with the ammo I want it zeroed for, then make my own notes at different distances and different ammo to learn the holds.
Velocity is the needed variable, regardless of barrel length which affects velocity but it is the ACTUAL velocity you want for ballistic calculations.

That is, the initial velocity, which in the case of guns is muzzle velocity, which slows throughout the flight due to drag.
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Old 08-07-2017, 05:34 PM
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I'm a new shooter but I took my 10/22 out the other day. Zeroed it at 25 feet then at 50 ft is all the high shots with red dot on center. I had to use ft because 50ft is the farthest my indoor range goes.

Still getting used to shooting but mine is way off hahahh. Have a scope now so next range time should be fun. My 15 22 is on its way, hopefully in 3 weeks.

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Old 08-07-2017, 07:16 PM
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Welcome to the forum. How high is the red dot? I ran your approx 8 yard zero with a sight height of 1.5" with a 40 gr bullet with a BC of 0.125 and muzzle velocity of 1200 (pretty generic). At 16 -17 yards (50ish ft.) it should be approx 1.25" - 1.5ish" high. How does it do with the hard sights? I think you'll really enjoy the 15-22.
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Old 08-07-2017, 07:26 PM
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...adjust it to shoot 1" high at fifty yards...that may get the trajectory right at the other points...
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Old 08-08-2017, 09:13 AM
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I'm surprised this got to post #13 before someone mentioned barrel length when talking about bullet drop!

You also need to chronograph YOUR ammo coming out of YOUR gun in order for the info from a ballistic program to be worth anything - SISO principle!
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Old 08-08-2017, 10:08 AM
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Most .22lr powder is done burning in a 16in barrel.

To experience an 8in drop at 100yds vs 3in would be the equivelant of that 36gr bullet with a rated muzzle velocity of 1260fps somehow falling to a muzzle velocity of under 1000fps. I seriously doubt that's happening.

There may be a bit of rated muzzle velocity loss, but I suspect the main culprit is your measured distances at the range or your sight over bore distance. Your numbers are suspiciously in the direction of an optic mounted low on an AR platform with no standard riser. Pics? Otherwise, the issue is somewhere in the measured distances you are using for zero or down field or both.

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Old 08-08-2017, 10:25 AM
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It would seem that the muzzle velocity is not exactly what the ammo says on the box.

It sounds like you have all the other factors figured out (sight height, zero range, bullet weight, etc) and they are easily measured either by ruler or by mfg statement.

One variable is obviously not right and I'll guess that it's honest to God muzzle velocity.
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Old 08-08-2017, 10:54 AM
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Quote:
Originally Posted by ChattanoogaPhil View Post
Most .22lr powder is done burning in a 16in barrel.

To experience an 8in drop at 100yds vs 3in would be the equivelant of that 36gr bullet with a rated muzzle velocity of 1260fps somehow falling to a muzzle velocity of under 1000fps. I seriously doubt that's happening.
Actually 16" is the point of diminishing returns in a semi-auto 22LR because that's where the bullet is when barrel pressure is low enough for bolt opening to start and that bleeds off the pressure in the barrel. I have an old model 69 Winchester (bolt action 22LR) that had a 26" barrel I shortened to 20" and lost velocity, and it got a LOT louder...

As to the bullet drop you need to know the bullet velocity, accurately measure the sight height and then carefully sight in based on your group center.

One thing I see is that the OP's 25 yd group is low. That really throws things off farther out. What I'd suggest is sighting in 1" high at 50 yds (one of the table distances and heights) so the group CENTER is 1" high,and see where the 100 yd groups are then.

OR, sight in 3" low at 100 yds and see where your closer up groups are. The farther out you sight in the less error you should have.

Just my 2 cents...
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Old 08-08-2017, 11:47 AM
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Quote:
Originally Posted by Blackstuff View Post
I'm surprised this got to post #13 before someone mentioned barrel length when talking about bullet drop!

You also need to chronograph YOUR ammo coming out of YOUR gun in order for the info from a ballistic program to be worth anything - SISO principle!
Not my experience at all with multiple calibers and weapons. Input the basic data fields and I find the calculators to be very close. 100 meters and in.
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Old 08-09-2017, 02:44 AM
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Quote:
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Not my experience at all with multiple calibers and weapons. Input the basic data fields and I find the calculators to be very close. 100 meters and in.
Well that likely means you're using ammo consistent with the claims on the box and a gun close to the gun parameters the ballistic program was designed around! It also depends on a persons definition of the word 'close'.
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Old 08-09-2017, 06:40 AM
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Default More confusion

The rifle is a Ruger 10-22 (custom built match gun) with a Simmons 6.5 x 20 x 50 MM (MidwayUSA $125) mil dot reticle scope. At 14X the crosshair is a 50 yard ZERO, 1 dot above the cross hair is a 25 yard Zero, 1 dot below the cross hair is a 75 yard zero, and 2 dots below is a 100 yard zero.

My target was a 11 meter air rifle target with 11 bullseyes on it. The range distances were measured, ammo was CCI HP MiniMags.

I tried other scope magnifications; 10X, 12X, 15X, and 20X; but had significant deviation from a "zero setting" . The 25 and 50 yard groups were one-hole 5/16" centered where the X-ring used to be. The 75 yard group was 1/2" centered in the black. At a 100 yards all the shots were in the black bullseye.

I have two M41 S&W target pistols with red dot sights, a CMore and UltraDot. At 75 and 100 yards, bullet drop is about 4" and 10"+ . Because of Dot size vs. Bullseye diameter, group sizes opened up to 3" and 5". My conclusion was that you can't shoot a small group if your dot is bigger than the target.

This is not an apples to apples comparison, but I believe it helps understand the difference between dot sights and scopes.
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Old 08-09-2017, 01:55 PM
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Quote:
Originally Posted by Blackstuff View Post
Well that likely means you're using ammo consistent with the claims on the box and a gun close to the gun parameters the ballistic program was designed around! It also depends on a persons definition of the word 'close'.
My "close" is within 2" at 100 meters with a 22 rifle, closer with an AR and much closer with lesser distant targets. Basic box ammunition of varying grains and bullet types. At a 100 and greater I typically use a LPV scope. I use calculators to get me within 4-5 inches at distances greater than 50 meters followed by an adjustment or two for elevation. Regarding calculator data, my normal input is pretty generic Normally the data is within 2" / occasionally 3" at 50. Side note: Not long ago I tried the 50 zero at 10 (AR) and was really surprised how close it was. All of my zeroing / testing is conducted using a single sandbag up front while sitting at an old government metal table. I would someday like to have a calculator which incorporates barrel length and other variables (if they exist) not typically found with online calculators. Don't know if I could do much better than I do now but it would be interesting to see if I could out perform myself with additional data while being limited to off the shelf ammunition.
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