Bullet Drop

[peterk123]

Question for you guys. I'm in the process of figuring out my DOPE for my 308.

Dead on at a 100.
Got my bullet speed.
Got bullet weight.
Have my BC....
Do the calculations.

Go to 200 yards and turn the dial per the results of the calculation. I'm off by a few inches, consistently. I need to add a couple of clicks.

Only thing that could be wrong is the BC. Is that possible? Or am I missing something? Scope appears to be taking just fine.

I'm going to 300 next. But I'm going to back into the drop based on my results at 200.

Any feedback greatly appreciated. Pete

 

[50wt]

Yes, its called truing . Best thing would be to shoot further out and adjust the bc from there.

 

[Broc]

Question for you guys. I'm in the process of figuring out my DOPE for my 308.

Dead on at a 100.
Got my bullet speed.
Got bullet weight.
Have my BC....
Do the calculations.

Go to 200 yards and turn the dial per the results of the calculation. I'm off by a few inches, consistently. I need to add a couple of clicks.

Only thing that could be wrong is the BC. Is that possible? Or am I missing something? Scope appears to be taking just fine.

I'm going to 300 next. But I'm going to back into the drop based on my results at 200.

Any feedback greatly appreciated. Pete

What is a "few inches"?

That is normal, it is very rare you will go from hitting X at 100 to hitting X at 200. But, you should be within MOA range and do the finer adjustment yourself. So, if your bullets are within 2-3" of the X, that is fine.

A lot also depends on the shooter. I have had days where I go from shooting 1/4 MOA at 100, to shooting 1 MOA at 300, because I am not having a good day, only to step away from the rifle, relax for a bit and shoot 1/2 MOA at 300.

One time I shot SUB MOA at 100, at 300 I was like 1.5 MOA, then I went to 600, stepped back for a while and was back to 1/2 MOA. That was a weird.

 

[Gator9329]

What's 1/2 moa at 600? A 1/2 a foot?
Must have been that relaxing nature walk to the 600 line. They put a fridge in that 600 house yet?

 

[Mountain]

Try one of the JBM Ballistics online calculators. Most versions will consider your scope centerline to bore centerline distance, which could account for some of the variance you are getting from 100 yards, which is a relatively short distance. To exaggerate a bit, imagine your scope is 6" above your bore and you sight in for 25 yards. If you don't account for that height, imagine how far off your 100 yard POI will be vs. what you calculate.

Actually I'm a bit surprised that you are off by inches at 200 yards from your 100 yard zero. For most typical calibers like 308 and 30-06, you can come up 2 MOA and you're going to be very close. For shits and giggles I plugged in .308 168 grain, 2700 fps, .5 BC, and 1.5" scope height (centerline). Results are 4" / 1.9 MOA drop at 200 with a 100 yard zero.

For my match M14 and M1's, the sights are 1 MOA per click. Guess how many clicks elevation either rifle gets when I move from 100 to 200 yards? Yep, 2.

 

[PatMcD]

100 to 200 is 2 minutes.
2 to 300 is another 2 or 3 minutes.
3 to 6 is another 11 minutes.

Maybe not an X, but on paper. Only your rifle, your loads, and your experience will give you exact the come-ups.

 

[BTSDOG]

Minutes of angle are:
1 in. @ 100yds
2 in. @ 200 yds.
3 in. @ 300 yds.
and so on.......

A 308 doing 2550 fps should shoot flat to 200 yds. Zero at 200 is best then figure bullet drop from there.....

 

[PappyM3]

Question for you guys. I'm in the process of figuring out my DOPE for my 308.

Dead on at a 100.
Got my bullet speed.
Got bullet weight.
Have my BC....
Do the calculations.

Go to 200 yards and turn the dial per the results of the calculation. I'm off by a few inches, consistently. I need to add a couple of clicks.

Only thing that could be wrong is the BC. Is that possible? Or am I missing something? Scope appears to be taking just fine.

I'm going to 300 next. But I'm going to back into the drop based on my results at 200.

Any feedback greatly appreciated. Pete

If the impact is off by a few inches at 200 from your calculation, then something is wrong. Could be your ballistic calculator is bad, or your bullet data is bad, your MV is way off, or you have the wrong height over bore set for your optic in the calculations (this is my first guess).

BCs can be off a little from the claimed value, and BCs do change as velocity decreases over distance. Applied Ballistics has some of the most true BCs. But at 200 yards, none of the BC variation is going to matter enough to change the estimated POI by a few inches.

What calculator are you using? What is the height over bore of your optic (actually measure it: centerline of bore to centerline of optic)? What is your bullet and MV?

 

[Mountain]

Minutes of angle are:
1 in. @ 100yds
2 in. @ 200 yds.
3 in. @ 300 yds.
and so on.......

A 308 doing 2550 fps should shoot flat to 200 yds. Zero at 200 is best then figure bullet drop from there.....

1.04", 2.08", etc. but close enough.

 

[PappyM3]

1.04", 2.08", etc. but close enough.

1.047”, 2.094”, etc. but close enough.

 

[Mountain]

1.047”, 2.094”, etc. but close enough.

 

[Broc]

What's 1/2 moa at 600? A 1/2 a foot?
Must have been that relaxing nature walk to the 600 line. They put a fridge in that 600 house yet?

Yes, 1/2 MOA at 600 is half a foot.

 

[HorizontalHunter]

Question for you guys. I'm in the process of figuring out my DOPE for my 308.

Dead on at a 100.
Got my bullet speed.
Got bullet weight.
Have my BC....
Do the calculations.

Go to 200 yards and turn the dial per the results of the calculation. I'm off by a few inches, consistently. I need to add a couple of clicks.

Only thing that could be wrong is the BC. Is that possible? Or am I missing something? Scope appears to be taking just fine.

I'm going to 300 next. But I'm going to back into the drop based on my results at 200.

Any feedback greatly appreciated. Pete

Is your bullet speed the paper speed or from from A chronograph?

 

[PatMcD]

Yes, 1/2 MOA at 600 is half a foot.

Ummm, nope. 1/2 moa at 600 is 3".

 

[Broc]

Ummm, nope. 1/2 moa at 600 is 3".

I know. I thought the face palm would be enough for people to know I wasn't serious.

 

[PatMcD]

I know. I thought the face palm would be enough for people to know I wasn't serious.

Good. I'm glad I didn't add "dumbass" at the end of that.

I tried to add a smiley at the end of this, but don't know how.
Feel free to call me dumbass.

 

[chris_1001]

I know. I thought the face palm would be enough for people to know I wasn't serious.

Another avatar? Lame.

I thought you were going this one?

 

[MisterHappy]

OP - are you pulling the trigger hard enough?



(there have been enough serious answers)

 

[chris_1001]

OP - are you pulling the trigger hard enough?



(there have been enough serious answers)

I add in some “positive vertical flinch” (pvf) to compensate for longer distances, more drop.

 

[MisterHappy]

I just meant that if you pull the trigger harder, you're adding more energy to the system, so it should increase the bullet's velocity, and therefore, reduce the drop.


But, I'm mainly a shotgun shooter, so it's not a big deal for me.

 

[namedpipes]

What is a "few inches"?

That is normal, it is very rare you will go from hitting X at 100 to hitting X at 200. But, you should be within MOA range and do the finer adjustment yourself. So, if your bullets are within 2-3" of the X, that is fine.

A lot also depends on the shooter. I have had days where I go from shooting 1/4 MOA at 100, to shooting 1 MOA at 300, because I am not having a good day, only to step away from the rifle, relax for a bit and shoot 1/2 MOA at 300.

One time I shot SUB MOA at 100, at 300 I was like 1.5 MOA, then I went to 600, stepped back for a while and was back to 1/2 MOA. That was a weird.

A-Hole

 

[chris_1001]

I just meant that if you pull the trigger harder, you're adding more energy to the system, so it should increase the bullet's velocity, and therefore, reduce the drop.


But, I'm mainly a shotgun shooter, so it's not a big deal for me.

I push out when shooting. I get another 3-5 fps that way.

 

[MisterHappy]

The NES firehose of info and great ideas, never fails.

 

[peterk123]

Try one of the JBM Ballistics online calculators. Most versions will consider your scope centerline to bore centerline distance, which could account for some of the variance you are getting from 100 yards, which is a relatively short distance. To exaggerate a bit, imagine your scope is 6" above your bore and you sight in for 25 yards. If you don't account for that height, imagine how far off your 100 yard POI will be vs. what you calculate.

Actually I'm a bit surprised that you are off by inches at 200 yards from your 100 yard zero. For most typical calibers like 308 and 30-06, you can come up 2 MOA and you're going to be very close. For shits and giggles I plugged in .308 168 grain, 2700 fps, .5 BC, and 1.5" scope height (centerline). Results are 4" / 1.9 MOA drop at 200 with a 100 yard zero.

For my match M14 and M1's, the sights are 1 MOA per click. Guess how many clicks elevation either rifle gets when I move from 100 to 200 yards? Yep, 2.

By inches I mean I have adjusted for the 4 drop already left the app.

So my bullet is behaving like it's going 2550 fps, not 2750 that I'm actually getting on the chrono. I noticed that playing with the altitude in the app makes a difference, so I made it 4,000 feet instead of 5,000. Helped a little.

Will be interesting to see the results at 300 meters, which is the next one out there at our range.

Is your bullet speed the paper speed or from from A chronograph?

Chrono

 

[peterk123]

If the impact is off by a few inches at 200 from your calculation, then something is wrong. Could be your ballistic calculator is bad, or your bullet data is bad, your MV is way off, or you have the wrong height over bore set for your optic in the calculations (this is my first guess).

BCs can be off a little from the claimed value, and BCs do change as velocity decreases over distance. Applied Ballistics has some of the most true BCs. But at 200 yards, none of the BC variation is going to matter enough to change the estimated POI by a few inches.

What calculator are you using? What is the height over bore of your optic (actually measure it: centerline of bore to centerline of optic)? What is your bullet and MV?

Hornady and the Sterlok. I'm going to change the scope height to see what it does. I am slightly higher than before because my objective is larger on the new scope.

 

[BTSDOG]

If you want to get serious, dont forget to factor in temperature and humidity.....

 

[peterk123]

Hornady and the Sterlok. I'm going to change the scope height to see what it does. I am slightly higher than before because my objective is larger on the new scope.

I actually had to drop the scope height to 1.25. Will see what it looks like at 300 meters next time I go out.

 

[PatMcD]

I actually had to drop the scope height to 1.25. Will see what it looks like at 300 meters next time I go out.

????
I'm trying to figure out how scope height above bore height would make any kind of difference beyond 100 yards.

Maybe I'm taking this thread too seriously.

 

[chris_1001]

If you want to get serious, dont forget to factor in temperature and humidity.....

Coriolis (sp?) effect. If you are a sniper, you have to factor this in after 25 yards ()

 

[BTSDOG]

And that will differ depending on which side of the earth you are on......or is it the equator......