Seekins Element 6.5PRC Load Dev. Next Step? [Update]

[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?

Thanks in advance!

 

[sndmn11]

All those options are the same.

58.2gr 2.347" cbto and go shoot.

 

[FattyBinz]

All those options are the same.

58.2gr 2.347" cbto and go shoot.

If they are all the same, is there a reason you are suggesting the one with the worst group, worst ES, worst SD, outside the node, lowest velocity?

 

[sndmn11]

If they are all the same, is there a reason you are suggesting the one with the worst group, worst ES, worst SD, outside the node, lowest velocity?

If it gets hot then you don't have an owie.

 

[bmart2622]

What charge weight did you hit pressure at?

 

[wapitibob]

I shoot 1 each in .5gr increments looking for pressure and vertical flat spot on target, then comeback and shoot 3 ea in .5gr increments spanning the flat spot I found earlier. The best charge weights will be apparent. I then go to 600 and for the 3rd check. No idea what es, sd, and velocity are and don't care. Some point in the future I might do seating test but not more than .005 either side of the original load, which is normally .010 off the lands.

 

[waspocrew]

Trying to find a difference between 0.1 gr is likely not going to happen. If 58.6 shoots to your satisfaction, I'd go with that. I don't worry about seating depth either. I start .020" off the lands and that's usually where I'm at in the majority of my rifles.

You will be chasing your tail trying to discern differences with minute changes in charge weight and seating depth.

 

[bmart2622]

And needlessly buring through components

 

[FattyBinz]

What charge weight did you hit pressure at?

59.0 gr is where I started to get a sticky bolt lift. Not bad, but noticibly different. 59.5-60gr is where I started to get some minor primer catering. 60.6 started some ejector swipes

 

[bmart2622]

If it were me, Id load 20 at 58.0grs at mag length, shoot 10 to get a zero and 10 to validate at distance and be done. Tiny changes in powder charge and seating depth are not telling and waste components

 

[sndmn11]

You could do a poll on here for n565/156 and 98%of people are 58.0-58.5gr.

 

[FattyBinz]

You could do a poll on here for n565/156 and 98%of people are 58.0-58.5gr.

That would have saved me a lot of time lol

 

[Koda_]

The question to ask is whats your max ES goal?
For me if your ES is under 20fps you have a good load. I would pick either your 58.6gn charge weight and see if its repeatable at .57moa grouping and call it good. Or, pick your 58.4gn charge weight which has a super low ES and play with a seating depth test to see if you can shrink your already respectable .75-1.0moa group size even more.