SD and ES in Magnum cartrigdes

[clrems77]

Recently developed a great load for my Remington 700 Sendero in 300WM. During the 100 yard development, the load shot very consistent 1/2" groups. I doped the gun out to 600 yrds with no real issues with accuracy, but im wondering what itll look like when I reach out further. I ask because my ES/SD was kinda high at 46/16 and 40/15 both times I ran the test group through the chrono. Anyone think these readings are normal for magnum or are they a bit high like im thinking? My load is as follows:

Winchester brass
75 grains of H-1000
CCI magnum primers
Hornady 208G Amax seated at 2.900@Ojive
Average velocity 2770

Remington 700 Sendero w/26" barrel and JEC brake.

Thanks for the help!

CJ

 

[LawnMM]

The rule of thumb I heard when starting out is you want an SD of 10 maximum, single digits is what you should strive for, and an ES under 30fps

At 100 yards an es of 40fps won't hurt you much, at 1000, or 1200, that variation will translate into large differences in where the bullet impacts vertically with regard to your point of aim. Purchase a copy of Accuracy and Precision for Long Range Shooting by Bryan Litz. It goes into a lot of detail as to how different factors affect your probability of hitting your target at different ranges based on how good your ammo is, how much error in your range finder, and your ability to read the wind down to "x"mph

Here is a brief overview of my reloading method that has served me well, I may work on putting it together into an article now that I'm on vacation again. Start by firing two rounds at each powder charge you intend to try working up to, and only if safe, a little beyond the powder manufacturers maximum. The purpose of those two rounds is to get a feel for velocity offered by the different charges, and to check for signs of pressure (sticky bolt, flattened primers, heavily cratered primers, ejector stamp on the case head). When you have a ballpark for the powder charge you want to use that offers the velocity that you are happy with...load 5 at the charge weight you like, and then another 5 .1gr higher, .2gr higher, and .1gr lower, and .2gr lower. Fire those 5 round strings over a chronograph and see how tight the numbers are. If you get good SD/ES, take that charge and group test it at 300 and/or 600yds and see how it does. I've yet to have a load with single digit SD not group well.

 

[Shoottothrill]

Yes on the Litz book. If you shooting out to 1000+ yards and you have an ES over 20 you are in trouble. Litz book has tables that will show you what an ES of 10 vs. 15 vs. 20 will do to your round as the range increases. The higher your ES the lower your hit percentage goes. I would strive to get that ES for sure below 20 and somewhere around 10 is optimal. Pretty tough to get below that I think.

 

[clrems77]

Thanks guys. Any ideas on how to bring it down? Primer change, seating depth ect?

 

[clrems77]

Can anyone educate me on fixing neck tension? My usual process is vibratory clean, full size bumping shoulder back .002, trim, chamfer in and out, ss tumble, dry, seat primers, dip necks in graphite, fill powder then seat bullet.