168 Amax and Ballistic Calc

[earplay]

Hi all,

I have been using the 168 Amax in my .308 with 45gn Varget, Norma brass, Fed LR primers. My velocity as chrono'd was lower than hoped (2635 in a 22inch barrel Rem 700sps), however ES and accuracy was great so stuck with the load.

I sited in at 100m, and then went out today at 446m. After several groups at this range, I found that I needed to adjust the velocity up to 2700fps in my ballistics calc for everything to line up correctly. I had made an effort to ensure all other parameters were correct.

I was wondering, is this a normal amount to have to tweak a calc by? I realise I need more testing at other ranges/conditions but wanted to know if I am on the right track?

Cheers,

Matt

 

[JeffP40]

Yep, pretty unusual for everything to go by the book. Get a very good zero at 100, then shoot at 2-3-4-5 and 6 if you can. Keep track of drops, and see how they match the chart. You can tweak the numbers (mostly vel and bc) to give you a drop chart to use at any distance.

 

[grit]

It is very normal. You want to validate your drops at several ranges in several conditions. You tweak velocity and BC until you have consistently accurate predictions. If you're using G1 BC you'll want to segment the BC by velocity. After a couple trips, you are "dialed in" and your predictions become very accurate.

There are a ton of variables. Chronos read high or low. Scopes track slightly more or less. All rifles will produce an individual BC for every bullet.