Long Range Considerations

A few rambling thoughts about long range zero's, reloading ect. that may kick off some intresting discussion. The wind discusions are always fun LOL.

A couple weeks ago my boy decided to put on a proper zero with a proper load on the .308 rifle he has been shooting as of late. It was pretty intresting watching it come together for him.

Last week he came up with a decent load for it Fed Gold Metal Match brass/175 grain Sierra BTMK's/ Fed GM primers and 45.3 grains of Varget. He's using GM brass because I have several 5 gal pails of it, it's not my particular first choice and the Fed GM primers are the only ones that will stay in the primer pockets after a few reloadings of the GM brass. The GM brass is "soft" and the GM primers are a bit bigger than othere brands and tend to stay in the primer pockets longer than other brands. He's using Varget powder because we buy it 64lbs at a time and 175's because they get bought 10k at a time.

He tried my TBA M40 load of 45.8 grains of Varget under a 175 for 2800 fps, but that dog wasn't hunting in his rifle, with the componets he was using. I use Lapua brass and CCI BR-2 primers in my loads, when he starts buying his own brass he can run the good stuff.

At 45.5 grains he was getting 2775 or so for a five shot average but his "ES" (extreme spread) was running in the 30's with a high teens "SD" standard deviation. He finally settled on 45 grains even for a 10 shot average of 2705 an ES of 18 fps and a SD running high single digits. This load gave him a nice two finger bolt lift and shot into 2 1/4" at 300 yards. I think he's going to stick with that load for now, he's about tired of load development.

ES is pretty important to me in my long range loads and I will trade velocity for low ES numbers any day. Usually I find that with the .308 that the hotter loads get pretty jiggy. Not uncommon IME to drop back a full grain from the top end of things only loose 25 FPS and get much better ES and SD numbers.

Yesterday he set up the 4'X4' target frame and set out to zero and seemed to be doing OK. I had ran out a Sierra ex ballistic chart for him and he went to work. Things went fine at 500 yards and he was holding a decent 1.5 MOA group in a gentle, but funky wind, that kept switching exactly .75 MOA from 3 to 9 and then 9 to 3.

Then he moved back to 600 yards and found the chart value to be 1.75 MOA low, he noted the change and didn't think much of it.

He was strung out pretty good at 700 yards from the wind, I think he was getting tired and missing the wind changes or just under doping them, that gentle wind was now sporting a 2.5 MOA value and just gently switching back and forth every few minutes. Never the less he could tell that he was now running about 1.25 MOA high.

When he got back to the house he showed me his notes and it confused me a bit, since the Sierra charts are usually really close. So I ran back out with him yesterday evening and I shot his rifle at 500 and found his initial zero to be a few inches low, he hadn't done a good job doping the center of his group or just had an odd flyer that had given him a funky group. I brought his 500 zero up and we shot 600 and 700 yard again with chart data and found things to be plumbed up.

What a difference it made to have a very precision zero. We got home and was going over the chart and found that what he actually had was a 475 yard zero and that accounted for his deviation from the chart values. You just got to love the ballistic programs! I ran the chart again for a 475 zero and that explained his dope changes at 600 and 700. Very cool.

It all had me wondering, that when we feel the need to touch up chart values, if the problem isn't more about the quality of the zero than the charts or maybe ES and SD isues as well.

Teuf,