velocity vs accuracy in long range shooting

[Bart B]

Originally Posted by Boss Hoss

Groups at 100 yards mean squat at 1k—there is No correlation at all . . . .

For example, a .308 Win. typically will have 2/10ths inch vertical shot spreads at 100 yards with 100 fps spread in muzzle velocity. Way down range at 1000 yards, that spread's about 40 inches.

And with a muzzle velocity spread of only 20 fps that might shoot under 1/10th inch at 100 yards may well shoot no better than 20 inches at 1000. Why? Unbalanced bullets will have different BC's and that's enough to cause big spreads in vertical shot stringing. 100 yard groups tend to open up about 10% for each additional 100 yards down range due to subtle winds as well as the 1% to 2% spread in bullets' BC's.

The old myth that a system making 1/2 MOA groups at 100 will also make 1/2 MOA groups at 1000 still prevails. . . . in some minds.

[Boss Hoss]

The other thing to remember is that while most folks load the “sexiest” bullet they can often time shoot no further than 300 or 400 yards. This is going to give everyone something to think about---BR shooters that shoot 100 and 200 yards use flat base bullets albeit many are custom but that is beside the point. There is a reason—sexy bullets are like fishing lures, they catch people more than fish lol. Now long distance rounds that will be going over 400 yards I use BT’s but that is my cut off. Don’t take my word for this --- talk to the ballisticians at the manufactures the BT’s take up to 300yards to completely stabilize. FWIW there is a lot of information out in the domain about this so it is not new by any means.

Also—when looking at trajectory at 1k take your high and low velocity and look at the vertical dispersion because it will open your eyes to see how important that is. The other point is when testing at long range or short NEVER chamber (just start it in the chamber not fed from the magazine) your round until the sight picture is perfect and the condition is right. Reason is that in a warm chamber will “preheat” your round which is a pressure variable that you do not want in load development or in competition.

[Bart B]

Originally Posted by Boss Hoss

Also—when looking at trajectory at 1k take your high and low velocity and look at the vertical dispersion because it will open your eyes to see how important that is. The other point is when testing at long range or short NEVER chamber (just start it in the chamber not fed from the magazine) your round until the sight picture is perfect and the condition is right. Reason is that in a warm chamber will “preheat” your round which is a pressure variable that you do not want in load development or in competition.

Good points.

I've tried to get my long range shots off between 10 and 15 seconds of chambering them. If they cook in the chamber longer than 20 to 30 seconds, the hotter powder shoots bullets out faster and they go high. So if the wind's changing and I need to keep up with it on the sights, I'll come down 1/4 MOA for every 30 seconds the round's cooked in the chamber. Works just fine. I've waited as long as 3 minutes and after coming up 5 or 6 clicks, put the next bullet down the middle. Then come back down 4 or 5 clicks and the hotter barrel's now back to shooting about normal for the next shot.

Conversely, there's been folks at the High Power Nationals with a match winning record setting score almost finished on the 1000 yard target and a cease fire was called 'cause of boats in the impact area on Lake Erie. If the wait before continuing to fire is longer than a couple minutes, competitors get one sighting shot before shooting the next record shot. A few have got the OK to continue after about a minute and a half wait and their barrel's cooled down enough that the next record shot didn't heat up enough in the chamber to shoot its bullet out as fast as the previous ones. That low velocity shot ends up in the 9 ring at 6-o'clock and they lose the match.