Seekins Element 6.5PRC Load Dev. Next Step?

[fattybinz]

Seekins Havak Element 6.5 PRC 21” with TBAC Ultra 7
Berger 156 Elite Hunter, N565, Federal GM210M primers, Lapua Brass twice fired, 0.002 headspace
CBTO: 2.347” (.010 off lands)

I’m coming to the end of the powder-charge portion of my load development and not sure where to go from here. I think I found a good velocity node from 58.3 to 58.6gr. Each charge weight in that string have good ESs and SDs. They are right below where I start hitting some minor pressure signs. Really happy with the velocities but I’m not sure which charge weight to use as I move on to adjusting seating depth.

Below is the data I’ve collected from these 4 successive charge weights. I know I’m only focusing on velocity right now but I’ve included the group sizes at 200 yards just in case it influences anyone’s advice. The group data are split up because they were shot on different days instead of all at once, so I measured them separately. There are also different number of shots because I initially wanted to stop at 58.4 but 58.3-58.4 shot so well I thought I'd go a bit farther with 58.5-58.6 to see if the node was bigger, which it definitely was. So I know it's not apples-to-apples comparison since there are a different number of shots for each, but I'm working with what I have right now:

Charge weight	# of shots	Avg Velocity	ES	SD	Groups at 200 yards
58.2gr	6	2863	26	9.9	6 shot 1.5 moa
58.3gr	11	2860	11	3.9	6 shot 1.46moa (.81moa with 1 flyer), 5 shot .86 moa
58.4gr	8	2865	8	4.7	5 shot 1.0moa, 4 shot .74moa
58.5gr	5	2873	12	4.9	5 shot .96moa (.61 moa with 1 flyer)
58.6gr	5	2873	16	7.3	5 shot .57moa

So options I'm thinking:
1. Go with 58.3gr because 1) it has the best ES/SDs considering/in-spite-of the larger sample size, and 2) it is in a VERY flat spot between 58.2 and 58.3. Cons: its at the beginning of the node and the charge weight just below it (58.2gr) had erratic velocities and the worst group
2. Go with 58.4gr because ES/SDs are fantastic and its in the middleish of the node
3. Go with 58.5gr because 1) it also is in the middle of the node, 2) also has great ES/SDs, 3) it has identical average velocity to 58.5, so it seems like a flat spot, 4) group wasn't bad, and 5) it has the highest velocities, and I'm trying to get every fps I can (wow...there are so many reasons here this seems like the way to go lol)
4. Go with 58.6gr because ES/SDs are decent and it has the best group (I know, 5 shots is a VERY limited set of data...your groups are too small...and I'm in the charge weight portion of load development but damn its tempting to go chase the small group)

So which of these options should I go with? Bonus question: As I move on to seating depth, what kind of increments should I test? I'm .010" off the lands now. So go back .005, .010, .015, or more?

 

[C.E.Smith043]

First question I have is, what is your intended purpose for this rifle? Deer hunting, competing, just for fun? Also,what distances are you expecting to shoot?

 

[fattybinz]

First question I have is, what is your intended purpose for this rifle? Deer hunting, competing, just for fun? Also,what distances are you expecting to shoot?

Sorry, I should have included that info. Mainly a hunting rifle. A few times a year I'll make my way to a range with steel out to 1200. For hunting, I'd like to be confident in what the rifle can do out to 700, although I'd only take a shot at that distance if conditions are perfect and I have all the time in the world (and there was absolutely no way to get closer). I know...I admit I may be nitpicking here...as all of these loads are good enough to give me that right now, but I'd just love if I can get this rifle to shoot .5-.6moa 200 and 300 yards.

 

[C.E.Smith043]

Are you currently using wind flags?

 

[fattybinz]

Are you currently using wind flags?

The range I go to has some flags up. Still, I only pick days with little to no wind to go work on my load development. The berms built around the range also do a lot to limit the wind down range

 

[Jager]

What I'd do is... repeat your ladder.

One shooting session, over flags (even if they're homemade ones). Same number of shots per increment. Gather velocities if you like, but don't expect your ES/SD numbers to give any insight into which group(s) are most accurate. Flat spots don't matter.

Probably most important... stop trying to second-guess your target. You're part of the rifle system and so stop thinking there's such a thing as a "flyer." The target will tell you the truth, if you let it.

Welcome to the forum!