Thread: Drop chart

Morning all. Wonder if someone with more ballistic knowledge than me could give me an idea of what the bullet drop would be with my 308. Ive chrongraphed the Sako gamehead thru My Bergara Extreme 18inch barrel at an average of 2680 fps.
Im sighting in 2 inches high at 100. Ive looked at ballistic calculators but im not sure im doing it right.
The bullet has a BC of G1/0.304 at 2680 fps.
I also chronographed Sako Gamehead Pro which interestingly group pretty much the same place as the gamehead soft point but was 200 FPS slower. I suppose thats because Gamhead Pro has a better bullet ballistically.
Any info appreciated.

What is your scope height above bore axis?

To find out, measure between top of bolt body and bottom of scope. Then add half dia of bolt body and half dia of scope.

The main reason the gamehead pro are grouping same spot is that they have only 7% less MV. Not enough to notice the difference at 100.

With your .308 at 2680 fps and a 0.304 BC, you’re looking at about 5-6 inches of drop at 200 yards and 15-16 inches at 300 yards. The Gamehead Pro grouping similarly but slower might be due to its design.

Will do Longshot. I suppose this would “scope height above bore”?
Got to go out with the other half at the mo. Ill get back asap

Originally Posted by Chunk

Will do Longshot. I suppose this would “scope height above bore”?
Got to go out with the other half at the mo. Ill get back asap

Correct, no rush. If you are inputting data into a ballistic calculator, you will need to play around with the zeroed distance until the calculator shows a 2" above sightline at 100. Start at around 170 and work forward. If at 170 it shows a higher POI than 2" at 100, work backward.

When you get to a point where it shows 2" high at 100, this is theoretically the distance at which your rifle is 'zeroed' in the true sense. You will then be able to input this zero distance for proper calculations.

https://www.huntingnut.com/index.php...intBlankOnline

Fill in the blanks and it gives you a graph very simple tool to use, even I worked out how to do it.

Sent from my cheap Chinese phone using the power of finger. 🤌

Originally Posted by longshot

Correct, no rush. If you are inputting data into a ballistic calculator, you will need to play around with the zeroed distance until the calculator shows a 2" above sightline at 100. Start at around 170 and work forward. If at 170 it shows a higher POI than 2" at 100, work backward.

When you get to a point where it shows 2" high at 100, this is theoretically the distance at which your rifle is 'zeroed' in the true sense. You will then be able to input this zero distance for proper calculations.

Ok , Thanks Longshot and Happy Jack.

I measured the scope height at 1.70 inches.
With your calculator Happy does that allow for my Zero to be 2 inches high at 100.?
Forgive my ignorance .

Yip you can make it whatever you want.if you right-click on finished graph it will allow you to store it. Can keep changing numbers n ranges till things make sense. Be aware to change temp n altitude to suit NZ. I usually use 1500 for altitude and 60 for temp.

https://www.jbmballistics.com/ballis...culators.shtml

This is an image of a very basic one I have used with the information listed in the above posts. It may vary in 'real life' but should be pretty close.

With your zero being 2 inches above zero at 100m you will find that you projectile starts its travel 1.7 inches below zero at the muzzle, will rise until it peaks at a little over 2 inches high at about 125m then drops to pass through your zero just after 200m and dropping a further 3 inches at 250m.

Essentially if you draw a 5 inch vertical line on a piece of target and a horizontal line 2 inches from the top of that line to form across and aim perfectly at that, it should hit that line as long as you are within 250m from it. (I doubt that there are many that are able to that accurately though) but with a hillar zone on a deer being about 12 inches you could aim at the centre of that and it wont matter how far that animal is as long as it is less that 250m you should hit it within 3 inches from centre plus your level of accuracy ). If you are capable of 2 moa accuracy with that rifle then add 2 inches up and 2 inches down at 200m for your group size



Does that help?

This should be what you’re after. It assumes 150gn projectiles, so if you’re using 165s let me know and I will rehash the numbers. Zero at ~194

Also measurements assume a 100yd (not m) 2” high sighting in. If you are using m instead I would rehash for this too. I can post the distances in m too if you prefer.

Just ignore the 2nd lot of charts, I can make charts but I cant figure out how to delete them out of a post........

Thanks Guys , very much appreciated. Got to say that Sako Gamehead is bloody accurate stuff in my Bergara. Half an inch at 100, which for me is friggin amazing. Certainly gives me more confidence now. Cheers very much.

I use this one.
Very simple to use.

https://www.hornady.com/team-hornady...alculators/#!/