Ballistics Math Check

[mac86951]

This is an exterior Ballistics Question.

I know that for long range, higher BC bullets trump velocity as long as accuracy isn't compromised, so here is the filler:

Distance: 600y
223 Wylde 20": 77gr Sierra going 2600fps at muzzle (back calculated), vs 69gr Sierra going 2900fps at muzzle, I'm interested in wind drift or choice in reducing potential for points errors.

Back Story: I understand that this is hard for many people to understand, but I like the challenge. I'm shooting an AR (20") at 600y with magazine length ammo (even fed from mag). I've been working toward finding a decent loading with 77gr and struggling, as I can't find a consistent loading beyond 200y, either because I'm horrible in the wind and need practice, or that I'm just pushing a loading that is ok at 100/200 that falls apart at longer ranges. I've had many good groups of 69gr at 100/200, but haven't bothered at longer ranges due to the difference of BC; however, after running the numbers in ballistics calc, I see a potential for ballistics to overlap between these two bullets at this range.

Given an overlap in ballistics for wind drift and all else being equal (I know that is a lot to assume), would one gravitate toward the higher BC loading, or would one gravitate to the lower drop loading?

I have posted this in the ballistic section as I already know that due diligence is for me to make sure "all else being equal" is fully evaluated.

Thank you,
-Mac

 

[Shynloco]

Mac,
I cannot speak to your issue in regards to the technical issue of BC in 69 gr vs 77gr bullets. And I'm new to the AR style shooting but many years of Benchrest & FTR style precision bolt gun shooting. But I note that you say you are having difficulty finding a load for Sierra 77's @ 600 yds. Don't know what powder you are using, but for what it's worth, my Gunsmith (who is building me a custom STTAR15 (24" JP barrel) essentially duplicating his STTAR15 20" barrel (JP Precision parts & barrel) that he shoots in 600 yd competition using 77 gr Sierra MK's magazine fed) uses 22.1 gr VVN140 as his go to load (col 2.260). Don't know if that helps or not, but worth a try if nothing else.

Alex