Why are my rounds dropping more then they should?

Ilove12gshotguns

Ilove12gshotguns

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Location
New Brunswick
Here's my load

308win
2.800 OAL
RL-15 @ 43.5G
FED 210M
165g SGK

22" Barrel
1-12 twist
Semi auto Browning BAR
Sight @ 1.1" above bore
Chrono'd @ 2665 fps +/- 15 fps

Ballistics charts tell me

100 - zero'd
200 - 4.3" drop
300 - 15.3" drop
400 - 33.5" drop

I'm getting
100 - zero'd
200 - 6.5"
300 - 21.5"
400 - untested

I stopped at 300m because I figured something was f-ed up.

How can a certain velocity vary that much from proven ballistic charts??? For me to get that amount of drop the rounds would have to be going 2050fps or slower, which I know is not the case.

I'm just scratching my head here....

Does this even matter if I know the fps, and the drop? Am I making a mountain out of a mole hill?
 
How many rounds did you fire at each distance to determine your drop? You have to account for group size at distance. Getting the center of a 10 round group at each distance will give you a better indication of the actual drop. Same thing for your 100 yards zero. Personally, I would zero at 200 yards for a hunting rifle and call it a day.
 
Leupold VX-3i CDS

It's my first scope I'm trying to play the "come up" game with.

Maybe the scope is buggered. It's the only thing I can think of. I hate to bad mouth a decent company like that but jeez, it might be pretty obvious it's the scope. I don't see how simple proven physics is somehow wrong.
 
Are your targets at the same level at each distance?

I was having a somewhat similar issue. What it ended up being was that when shooting off the bench at my range, you are shooting at a downward angle towards the 100y targets, and a slightly upward angle for 200y.

The result was that i was seeing 1" less drop from 100-200 than i should have been getting. Had this issue with multiple rifles. It wasn't until i started asking fellow shooters about it that i found out others were getting the same thing.

I started zeroing from prone at 100y, so i was closer to level with the target.
Then when i moved back to the bench for 200y, my drops then matched up (and subsequently matched when shooting out to 600m)

May not be your issue, but something to check out
 
RangerPark said:
How many rounds did you fire at each distance to determine your drop? You have to account for group size at distance. Getting the center of a 10 round group at each distance will give you a better indication of the actual drop. Same thing for your 100 yards zero. Personally, I would zero at 200 yards for a hunting rifle and call it a day.
Click to expand...

This is where I would start.
Fire 6-7 rounds at each distance and measure the drop to the center of the group.

Have you had the dial inscribed for that load already? (are you using the CDS feature for this test??)
 
I have the CDS scope, but not the inscribed dail. Just using the marking on it in MOA.

I will have to whip up another 50 rounds and fire 5-8 rounds at each range with the scope zero'd at 100m. I will hold dead on at the target and let the round "drop" what they want with no hold over.

I will post the results in a couple of days. I'm guessing it won't be earth shattering news. Just a scope that won't track, and I will have to bring it in for warranty work.
 
Bullet BC=0.404, stated velocity is very close in my Lyman Reloader's manual to your chronographed 2665fps. My ballistics program is within 0.1" of your predicted values. The only thing I can think of is your scope. Did you verify it's still zeroed at 100y after shooting your groups at 200 and 300? You stated a scope height of 1.1". That is very low. Did you measure from the centre of the scope tube to the centre of the bore? It appears you measured from the centre of scope tube to the top of the barrel. That shouldn't make up the difference in drop though.
 
Have you done more than one test???? Did you work up your load on a hot day and shoot on a cool day??? Was there a significant elevation difference?? Are you shooting through mirage??? Downdraft????

Temperature can have significant effect on point of impact. For instance, bright/hot conditions on the 100yd range can cause your point of impact to be higher and when you shoot further out, under different conditions the bullets impact will be lower.

One thing that catches a lot of people is they sight in on the flat for 100 yds and shoot longer distances at uphill or downhill targets. Shouldn't make that much difference though.

This is my problem with Chronographs. They don't always give factual velocities. They are great for establishing whether your velocities are consistent though.

Your range test indicates a lower muzzle velocity than your chronograph indicates.

My charts are appx 100 fps slower than than your chrony indicates.

Good bullet, decent velocity. If it meets your accuracy criteria, use your existing load and apply real, in the field data to compensate for bullet drop.

The only way to guarantee the same performance indicated by your manuals is if you can EXACTLY DUPLICATE THE AMBIENT CONDITIONS on the day the tests were recorded, likely in a controlled facility.

Get close and call it a day.


TURF THE LIBERALS IN 2019
 
Ilove12gshotguns said:
I have the CDS scope, but not the inscribed dail. Just using the marking on it in MOA.

I will have to whip up another 50 rounds and fire 5-8 rounds at each range with the scope zero'd at 100m. I will hold dead on at the target and let the round "drop" what they want with no hold over.

I will post the results in a couple of days. I'm guessing it won't be earth shattering news. Just a scope that won't track, and I will have to bring it in for warranty work.
Click to expand...

Do a box test at 100y to see if your scope is tracking properly
 
Just did some testing with your info, what chronograph do you use? I checked numbers changing the chrono distance and got numbers very close to your actual results. Worth a look anyways.
 
Just did some testing with your info, what chronograph do you use? I checked numbers changing the chrono distance and got numbers very close to your actual results. Worth a look anyways.
Click to expand...

This matters?

I always just put the chrony about 1 meter from the muzzle and go nutz. There is so much i don't know about this reloading thing

I use the cadwell budget chrony.
 
Ilove12gshotguns said:
This matters?

I always just put the chrony about 1 meter from the muzzle and go nutz. There is so much i don't know about this reloading thing

I use the cadwell budget chrony.
Click to expand...

Yup. Most programs will have you put in the distance from muzzle to chrony. Also having the chronograph too close can mess up your readings from particulate/smoke etc. should set it around 10ft out for best results.
 
Ilove12gshotguns said:
I always just put the chrony about 1 meter from the muzzle and go nutz. There is so much i don't know about this reloading thing
Click to expand...

That's what I used to do. Then I got a .300 Win Mag and the muzzle blast blew the sun screens clean off the chrono. It was actually quite comical. Like it's been mentioned already, 10 feet is more like it.
 
RangerPark said:
That's what I used to do. Then I got a .300 Win Mag and the muzzle blast blew the sun screens clean off the chrono. It was actually quite comical. Like it's been mentioned already, 10 feet is more like it.
Click to expand...

I put my cheap RCBS chrono 10 yds out for 338 and 375. Otherwise the muzzle blast gives unreliable readings.

OP, what ballistics chart or app are you using?
 
Most likely the chrony readings were inaccurate. Sierra is usually pretty good with BC ratings. I doubt a new Leupold scope is faulty but it wouldn't hurt to do a box test. Also double check if it's true MOA adjustments or IPHY. It makes a bit of a difference.
 
Ilove12gshotguns said:
Here's my load

308win
2.800 OAL
RL-15 @ 43.5G
FED 210M
165g SGK

22" Barrel
1-12 twist
Semi auto Browning BAR
Sight @ 1.1" above bore
Chrono'd @ 2665 fps +/- 15 fps

Ballistics charts tell me

100 - zero'd
200 - 4.3" drop
300 - 15.3" drop
400 - 33.5" drop

I'm getting
100 - zero'd
200 - 6.5"
300 - 21.5"
400 - untested

I stopped at 300m because I figured something was f-ed up.

How can a certain velocity vary that much from proven ballistic charts??? For me to get that amount of drop the rounds would have to be going 2050fps or slower, which I know is not the case.

I'm just scratching my head here....

Does this even matter if I know the fps, and the drop? Am I making a mountain out of a mole hill?
Click to expand...

There have been excellent suggestions on how to diagnose your concerns.. but I would like to add another suggestion and that is the SEMANTICS of how you describe drop and come ups. Just helps to resolve any confusion to ensure everyone is on the same page.

When shooters discuss the physical drop on a target, they should mean that a very tall target is set at 100yds with the impact zero'ed... then the target is moved in 100yds increments and shots fired aiming at the same spot used at 100yds and measuring (tape measure) the location of the impacts at each distance. You are literally measuring the DROP from the aiming point. This will be reported in inches as you list in the first post.

When shooters discuss drop as it relates to MOA or mils, they are indicating the value of the scope adjustment so that the point of impact is ON THE TARGET at varying distances. When you aim at a target further away, you will be adding UP elevation in your scope.

I assume you had targets at the various distances and adjusted the scope until the bullets HIT THE TARGET? We would report our adjustment in MOA or mils and leave it at that. Maybe you have now converted that BACK to inches and maybe the math is off?

For simplicity, I would suggest you forget about discussing drop as the vertical "fall" from the POA but how much scope adjustment you have added to put the bullet on the target at distance.

It eliminates the reverse math that can get ooop'sed. It is in a language that all LR shooters will understand and it is really easy to see if your scope is wonky or your ballistic solution out to lunch.

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

JBM ballistics is freeware that is pretty much universal and accessible to anyone on the internet. Entering your data, here is the adjustments you should apply to your scope to hit the target at various distances... you can muck about with the settings as you wish.

100yds ZERO
200yds +2.1 MOA
300yds +5 MOA
400yds +8.4MOA
500yds +12.5MOA

Assuming your scope has 1/4 min clicks, just dial to the closest 1/4 and send it... Now you can see on your target how far off your impact is to predicted. If the bullets land within the group size of your rifle and ammo, on the target, call it good and enjoy.

If the group is way off, then recheck the velocity with a different chrony (I recommend a Magnetospeed or labradar) and also do a box test to see what the scope's adjustments actually do.

New scopes can fail...

Jerry
 
Ilove12gshotguns said:
308win
2.800 OAL
RL-15 @ 43.5G
FED 210M
165g SGK

22" Barrel
1-12 twist
Semi auto Browning BAR
Sight @ 1.1" above bore
Chrono'd @ 2665 fps +/- 15 fps

Ballistics charts tell me

100 - zero'd
200 - 4.3" drop
300 - 15.3" drop
400 - 33.5" drop

I'm getting
100 - zero'd
200 - 6.5"
300 - 21.5"
400 - untested
Click to expand...

What type of rings are you using to get that scope so low to the bore?
 
Ilove12gshotguns said:
I have the CDS scope, but not the inscribed dail. Just using the marking on it in MOA.

I will have to whip up another 50 rounds and fire 5-8 rounds at each range with the scope zero'd at 100m. I will hold dead on at the target and let the round "drop" what they want with no hold over.

I will post the results in a couple of days. I'm guessing it won't be earth shattering news. Just a scope that won't track, and I will have to bring it in for warranty work.
Click to expand...

Between you doing what you stated above and the similar recommended advice by Mystic-Precision above you should be very well off with the scope corrections.
 
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