Point of Impact Prediction

nico21s · Rookie Member Joined: Jun 16, 2011 Posts: 3

Hi Dallan,

Thanks for a wonderful program to calculate trajectories.
I carry my trajectory card in my pocket when out there.

I have a favourite load, optimised for hunting and accuracy in my rifle for bushy area.
I have another load, with a lighter faster bullet for plains.
The third load I have is a cheap bullet for shooting club shoots and not using expensive hunting bullets.

Is it possible to predict the point of impact of the lighter and match bullet when the rifle is zeroed using the hunting load?
Basically if the rifle is zeroed at 100m with the hunting load, the lighter load would be shooting higher/lower at 100m and will be at zero at a different distance. The same holds for the match bullet.

I can model the trajectory of each load based on a specific zero. The option is to shoot the different loads and by trial & error determine the point of impact and zero range for the other bullets. It would however be handy if one could get an estimate of impact to make life simpler and save the ammo for the actual shooting.

Do not know if this is a ridiculous idea... but that is what computers are for.

Thanks
Nico

Elvis · Posted: Tue Jan 08, 2013 1:05 pm Post subject: Re: Point of Impact Prediction

welcome aboard nico21s
I use different loads through my rifles and I believe the easy way to get what you want is to sight in your main load then fire a group from your other two loads to find thier POI at 100 yrds or better still chronagraph them. the POI should enable you to use the system to give you your trajectory by putting in your data and keep changing your sighted in range untill you get the bullet path to intersect at 100yrds at the same height as your group. then you will have the correct path plotted??

Elvis · Posted: Tue Jan 08, 2013 1:11 pm Post subject: Re: Point of Impact Prediction

using the different ballistic coefficent in the data if all else is the same MAY give you the desired result but I believe you will still need to poke holes in paper to check. and with a lighter load you would be very very lucky not to need it.
my .270 has a nice accurate 130grn load and a 170 grn load for in the scrub, both pattern together at 100yrds so its not a big deal at all. I guess it is a matter of what range you are talking about as up to 100-150yrds on body shots for deer it shouldnt make a huge difference but if you are talking longer range or smaller target well I think you wont beat poking holes in paper.

nico21s · Rookie Member Joined: Jun 16, 2011 Posts: 3

Hi Elvis,

You mention exactly the way I intend to do it with the current setup.
I just need to chronograph the match load to get the trajectory accurately plotted on Point Blank.

Good excuse to get to the range... Smile

Pumpkinslinger · Posted: Tue Jan 08, 2013 9:10 pm Post subject: Re: Point of Impact Prediction

You could compare trajectories but the only way to compare points if impact is to shoot them. There isn't much way to calculate the barrel vibrations, etc. that would affect POI.

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

Pumpkinslinger wrote:

You could compare trajectories but the only way to compare points if impact is to shoot them. There isn't much way to calculate the barrel vibrations, etc. that would affect POI.

IMO this is what I've found in the field. You can sight in for one type of ammo, then shoot test groups with other types of ammo. Record the MOA shift from your primary load to the secondary types then just adjust your scope to the new types.

-DallanC

TRBLSHTR · Posted: Wed Jan 09, 2013 12:07 am Post subject: Re: Point of Impact Prediction

I do like Dallan says-plus tape a"doping card" to the stock on my rifles to kinda take out the guesswork!

Aloysius · Posted: Wed Jan 09, 2013 2:53 am Post subject: Re: Point of Impact Prediction

And then don't make mistakes: sometimes "UP" means cross goes up, sometimes "UP" means POI goes up.
And the same things can happen with "L" and/or "R"...
remember: your right hand is where your tumb is pointing left. Smile