Standard Deviation: 100yd groups "vs" 1000 yard groups ?

[Beelzebub]

While not an expert at reloading I do understand most things I read and hear about it. But I have a head scratcher for you LR pros.

I've reloaded for 5 calibers over the past week trying to get read to go to a 1100 range with some friends I've never shot with before. I can't just take my stuff to the range and drop the tail gate. I have to be methodical and "impressive" with/about it! ;-)

So I bought a new Caldwell chronograph and so far it has been way more accurate Shooting Chrony I wound up shooting on purpose.

So while I was shooting for groups and a good zero, I was recording velocities. My 338 Lapua stayed in the 6-7 range, 308 Win in the 5-6 range, 6.6 CM went up to 17 and 243 was about 12. 223 Remington finished in the low 20's.

As I understand it, smaller calibers tend to run higher in SD's than larger ones. Having said that, my best groups of the five calibers were with the 243 @ .234" and the 6.5CM at .416". 308 and 338 stayed around .650 - .800. Will definitely do some tweaking on them before I settle on a load. The 243 loads were some of 500 107 SMK's I bought in 2013 and loaded in December of 2013. They were shooting 0.195 and smaller. Probably have shot 2-3000 rounds down the barrel since I shot those and could not for the life of me get them under .234" Was also disappointed in the CM load. It had been shooting 0.233 last month.

So here it is; best groups were with two of the highest SD's. That didn't seem to affect them at 100 yards, but is this high SD going to send my groups in to a whirl wind by the time it travels another 900 yards?

Thanks in advance for informative replies.

Bee

 

[wbm]

Short answer yes. You can get an idea of the change from 100 to 1000 by simply running your numbers through a ballistic program. Go to places like http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi and check out your results.

 

[dmoon]

The standard deviations are going to apply more (meaning not only) to your vertical and changes in the wind are going to apply more (again not only) to your horizontal. And your form/methodology is going to apply to everything always....

 

[Joefrazell]

The sd and ES will show up.down range but not so much at other 100. Also it's possible to have a very low sd and still have a load that just doesn't shoot as well as another. They don't always go hand in hand. Shooting 1100 it's gunna be more important to have a load that shoots low sd's. As long as it's shooting under moa I'd choose it over a one hole group that's sd is in the 15-20. Another thing is your crono probably not that precise.

 

[Beelzebub]

thanks guys.

In fact my lowest SD's were some of my worst groups.

Going to let the 308 and smaller rest for a few days and work on my Lapua for a few days.

Have loaded up 4 diff loads using Hdy 200 SP with Retumbo and H1000 and Hornady 230 ELDX with Retumbo and H1000.

I have RL26 22, 19, IMR7828 if anyone has any recommendations with these.

tks in advance,
Bee

 

[coyotelite]

you're neutering that lapua with anything less than a 250g slug. I would bet that rifle will shoot a 250 or 300 berger with h1000 behind it much better than the lighter 200 and 225's. that being said, higher sd's regardless of 100 yard group will foul your dope at distance. lower sd's will give you a true dope but if the rifle doesnt like the load whats the point. I would keep working until I found low sd and sub 3/4 groups across the board. different bullets, powders, neck tension, head space etc.

 

[nmbarta]

I agree 100%, the 300 @ 2800 ish is tough to beat. I get 2820 with single digit sd's with retumbo and 215m's. 29" barrel.

A 30 fps spread with cost you well over 1/2 moa at 1000, with most combo's out of the 338 lapua. That pretty much takes you out of the game.