Help me with these chronograph results

[theCZ]

NOTE: I also posted this on the "Varmints Den" forum. Also, Please don't try to duplicate my loads, I know they are safe in my rifles.



Help me with these chronograph results
I've been tinkering around with a used 700 in 6mm Rem. that I picked up for a great price. I got a change to spend some time with a chronograph today. I also chrono'd two rifles, a CZ527 .223 Varmint Laminate, and a CZ527 .223 American. Here are the results, maybe you could help interpret them:

Remington 700 6mm. 80g Sierra Blitz
Chronograph results:
Date: 9/23/2007 Load: 48.0g H4831
Results: Average: 3069.80
3083 High: 3085.00
3057 Low: 3056.00
3056 Std. Dev. 13.81
3085 Extreme spread: 29
3068
-I was interested to see the 1st and 4th have virtually identical velocities, as well as the 2nd and 3rd. Does this help explain why I am getting two tight clusters instead of one? I haven't done much testing with powder, but this load was the most accurate for me. Also, the two clusters are spaced horizontally, even with zero wind conditions.

Now onto the 223 Varmint, this rifle has always been very accurate for me and the results don't really need much interpreting as I see it.
Date: 9/23/2007 Load: 50g Blitz 26.0g H335
Results: Average: 3392.00
3398 High: 3407.00
3407 Low: 3369.00
3369 Std. Dev. 14.14
3391 Extreme spread: 38
3395

With the 527 American I had a bit of a surprise. This rifle gave me the smallest group I've ever shot with a factory rifle a few months ago, 5 shots into .28" at 100yds. I've used this rifle to take about a dozen coyotes on our ranch this winter. I'm shooting Sierra 50g Spitzers.
Date: 9/23/2007 Load: 27.0g H335
Results: Average: 3476.40
3539 High: 3539.00
3479 Low: 3393.00
3487 Std. Dev. 52.56
3484 Extreme spread: 146
3393
The last shot really seems odd. Should I count it as a low powder charge?



Any tips on how to obtain more even velocities?

 

[jeepmor]

From what I learned here on THR, I'd go this route. If you've already done them, proceed to next one. All this assumes you are using the same brand of brass in each group.

1. hand trickle charges to exact weight spec, run up or down by 0.2 grains to see if groups tighten or speeds get closer or wider in spread.
2. Chamfer flash holes for consistent ignition.
3. Make all primer pockets consistent depth.
4. Weigh cases, match accordingly. Consistent weight usually implies consistent internal volume.
5. Turn the necks for consistent tension on bullet.
6. Measure the volume of each case and match that way.

Beyond that, somewhere after number 2 I'd be buying some match grade bullets and playing with the seating depth. I think you are doing pretty darn good already. Throw some commercial ammo downrange for comparison, I think it will illustrate that you are doing pretty good already. Except on that 527, something went awry there. Roll up the same charges and try again there, the others, that's pretty good I think. But I'm still learning myself and have been diggin through here for tips on the elusive one hole group. A lot of factory ammo has a stout crimp on it, this makes the bullet tension more consistent, and the starting pressures more consistent in turn.

Hope this helps, I'm not there on mine, but did get 0.6 groups out of my hunting rifle and if I could be more still, I think they would have been even smaller, not sure. Good enough for my hunting rifle, haven't got back to the reloading of my rifles just yet with deer season starting next week.

 

[theCZ]

Those are some darn good ideas. I've been reading a lot about neck turning and primer pocket uniforming. I enjoy reloading enough that I think it would be worth it. Right now I'm using a digital dispenser, but it's only accurate to .1 of a grain, I think I'm going to use it to dispense a load close to what I need and then put it on a balance beam scale and trickle to exactly what I need.

I think I'm going to be doing some more testing soon.