new chronograph; questions on results

[Ed333]

As a new reloader, I had not measured velocities until today. I took my 6BR to the local 100 yd range along with my new chronograph, fired 20 of my reloads (105 gr moly A-Max, 29.0 gr. Varget, jumped .020"), five to get my zero (scope had been set for 600), and then five 3 round groups. I then finished off 12 rounds of Lapua Scenar 105 gr. factory ammo from a single lot, followed by two orphan rounds of same from a different (older) lot. Here is my puzzlement, the Lapua Scenar string from the same lot had an average velocity of 2791, ES of 35 and SD of 11, and was giving me one-hole groups. My reloads had an average velocity of 2716, ES of 28 and SD of 8. But not shooting groups as tight as the Lapua factory ammo was, although with better ES and SD. Am I missing some basic point here? Or are those variances in ES and SD not significant?
btw, the ammo from the older lot of factory ammo varied greatly from the newer lot of factory, adding that in to a string of five with three from the newer lot gave me ES of 81 and SD of 30. Maybe that is not enough to give a valid comparison, but I found it striking.

 

[DennisH]

Here is my puzzlement, the Lapua Scenar string from the same lot had an average velocity of 2791, ES of 35 and SD of 11, and was giving me one-hole groups.

You could fine tune the Scenar's and lower your SD,

My Br loves Scenar's and JLK's, and my BRX loves 107 smk's, FYI

The 6BR is usually pretty easy to tune. Give us barrel length, twist, action and we will see if we can help you out further.

Dennis

 

[savageshooter86]

I believe low SD and ES really help long range shooters? IF your gun shoots at distance consistently, I personally would think not to worry about what chrony is telling you

Might be you just need to tweak your load every so slightly to get them shooting good

 

[Steve Blair]

At 100 yards, group accuracy and velocity extreme spread have very little to do with one another. I've known point blank BR Shooters that did not own chronographs. They just didn't care about anything but groups. Long Range shooting, past 600 yards, requires low ES in order to maintain minimum vertical dispersion. I will not shoot a 1000 yard load over 15 fps ES and prefer under 10. My current .300 WSM match load averages ~9 fps ES. [br]
My load development sequence goes like this: [br]
1. Set charge for best ES and node width.
2. Set seating depth for best accuracy at charge above.
3. Refine grouping with tuner. [br]
The reason for adjusting seating depth and setting the tuner is that barrel timing and harmonics do not always coincide with optimal powder burning characteristics. Adjusting seating depth will alter barrel timing and the tuner will alter barrel harmonics. All three are required for a successful long range load. Using this approach, my .300 WSM, running 230 Hybrids at ~2865 from 34", shot the attached group at 100 yards. It also performed very well at 1000. I took this load directly to Raton having never shot it past 300 yards, and then only for zero.

 

[Ed333]

Thank you Steve, your sequence seems very logical. I was getting thrown a bit by the new Berger manual, with its section on seating depth, it left me with the impression that you started with seating depth, and then tinkered with powder load. Or maybe they just assumed you had your best powder load determined already, and were taking it from there. In any event, I misunderstood, and burned a lot of powder to little or no avail.

On the other suggestions re bullets, the Scenars were in newly purchased Lapua factory ammo, I wasn't going to fool around with the cartridges. I wish I knew what powder Lapua used in that ammo, it is pretty decent stuff.