velocity, chronograph, hornady, .308, a-maxI’m looking to use a ballistic calculator to set up a good drop table for one of my rifles, but I don’t have access to a chronograph. Hornady claims that their 168 grain .308 A-MAX load achieves 2700 feet per second from a 24 inch barrel (same length as my rifle, so that’s not a variable). Given such an even number, I have some suspicion that there’s some rounding going on. Has anyone chronoed this round to verify Hornady’s velocity claims?
Actual velocity is going to vary by environmental conditions as well the rifle itself (twist rate, barrel condition). I see a few chrono’s for some shorter barrels over on SniperCentral and some seem to fit the 100fps loss per 2” ballpark and some don’t, in both the faster and slower direction. To get the most accurate drop table, you’re probably going to have to borrow a chrono from someone. Lacking that, you could start with the manufacturers numbers for now and see how it compares to the real world and maybe calculate back from there.
2700fps with a 168 is a feasible speed though it is pretty much “full power”. It’s possible that factory ammo might deliver this but it is also possible that the typical velocity might be lower (and @OldWolf’s link to a SniperCentral post has somebody reporting about 2450fps, which is on the mild side). Ammo factories are sorely tempted to claim high(er) speeds, but they are also very strongly motivated to not make ammo that is too hot in some of their customers’ rifles.
If shooting at modest distance (say, no more than 600 yards), being wrong in your m.v. by 100fps won’t make a terribly huge difference.
Without a chrono, if I was to do this I’d make up a table based on an m.v. of 2600fps (based on a SWAG that if the factory velocity claims are wrong, the true m.v. is likely to be a bit lower rather than a bit higher).
Have a look at the loading tables at http://data.hodgdon.com/cartridge_load.asp for .308 Win to get an idea of typical max loads for a .308/168.
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