Help reading groups for seating depth test (pics)

[4xtrak.chmp]

This is my first seating depth test and from what I understand I am looking for 2 nodes that are together and not just 1 kickass group. I think I see where I want to be but could really use more experienced eyes on my groups and hopefully shed some light on what you see ! Don't know if all this is relevant or not but here is the gun and the load.
Tikka tac a1 t3x 6.5 CM using a factory barrel suppressed
My load is 41.2 gn of H4350 with 143 gn hornady eldx bullet. I wont bore you with anymore unless needed.

Exclude # 1....I goofed that string up
3 shot groups

 

[ShtrRdy]

As far as choosing loads that are in the same spot, (point of impact), to each other, I use the OCW approach to do that. Then I will try different seating depths and choose the best group. I'd load up some more at 2.264 and see if it will repeat.

 

[DownhillFromHere]

OP, you have a charge weight of 41.2gr H4350 with a 143gr bullet - squarely in the H4350 "window" for that weight range bullet - and you have several targets showing quite competent grouping. I'd say you're mostly where you need to be; pick one of those depths and run it.

I used to get all weirded out because I'd do a range trip and get my normal 1/2" 5-shot group with whatever caliber - but that group would "move" in relation to point of aim. Then, after being pointed to it by someone here on SH, I started watching the Hornady podcasts (#50, #52) regarding sample size of groups. Basically, after firing thousands of rounds in a controlled environment, conclusions were... well, watch for yourself.

After watching, I went out with my long-tested 6.5CM match load (Berger 140 Hybrid Target, 41.2 H4350, CCI450 in Peterson SRP brass) and fired four 5-round groups at 100 yards on a calm morning. I got four 1/2" groups as usual - but if I overlaid the four groups into a single 20-round group, it was more like 3/4" - as predicted in the podcast. I set my POA to match the combined-group average POI and haven't looked back.

I did the same thing with my 6BR, which has supplanted the 6.5CM for most match use and produces slightly smaller 5-shot groups. I did that testing on a 100-yard indoor range, so guaranteed consistent 1-2mph "wind" from my 6 o'clock (vent fans sucking air downrange). Results were the same - 20-shot aggregate group half-again the size of any of the five-shot groups.

Had I run 30-shot tests, I'm confident that the groups would have been a bit larger still (the Hornady guys ran tests into triple-digit sample sizes and determined that 20 was an optimal return-on-ammo-investment sample size and more than 30 was a waste).

Podcast #50 is below. Links to #52 and other relevant testing/analysis will appear as usual on Youtube.

Hope this helps - it was certainly useful to me, and I fired nearly 600 rounds of 6BR chasing "perfection" in a new rifle - I'll never do that again.
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EDIT: @Wiillk is correct in his assessment below. While looking for an optimal seating depth, confirmation of promising-looking depths by firing additional rounds is in order. With that said...

... I just noticed that the tested depths in your second photo are only .012" min-to-max, and all of those groups look pretty good to me. One of Berger Bullets' Tech Talk articles - I didn't look for the exact one - describes an optimal seating depth node as being ~0.015" wide - and your groups show that.

I tested my 6BR depths 0.020" apart and verified the best by firing more groups 0.010" apart. Reality is that barrel erosion is going to quickly erase really tight depth "nodes."

 

[Dead Eye Dick]

It looks to me that you shot one group for each seating depth. I have no problems with three shot groups or five shot groups, but I think it takes several groups at each seating depth (or any test load, to determine a pattern. Picture below is what I mean. Testing a new bullet in a rifle that has been a bit of a problem child. If I took the first group, I would have never considered the load to be working. Yet the next two groups show a positive pattern. Just my two cents. If you shot more groups per seating depth and did not mention it, please disregard. (And accept an apology.

 

[Pharmseller]

You’re a LOT better than I am if you’re finding significance in a difference of 3 thousandths.




P

 

[Chris1972]

I’ll be testing the same way in the morning. All bullets are currently loaded .003” off and I will be stepping in .003” steps. Starting long and seating them shorter at the range will allow me to test the better ones multiple times in one session without wasting ammo on the bad ones. This will be a first for me dragging a press to the range.

 

[4xtrak.chmp]

I certainly appreciate all the responses. I will take this info and proceed with some more groups (those were the only groups Wiillk )from the same test and go from there.

I didn't even know about the hornady podcasts......great info there as well. Thanks to all !

 

[MarkyMark007]

your groups are ALL the same. just pick any your load; they all shot the SAME.

if you test for powder charge and seating depth, take LARGE steps. like at least 1gr of powder and 0.050'' jump.

if you test 0.003'' difference of OAL and 0.2gr difference of powder charge, your group difference will be only in your HEAD!!

 

[straightshooter1]

This is my first seating depth test and from what I understand I am looking for 2 nodes that are together and not just 1 kickass group. I think I see where I want to be but could really use more experienced eyes on my groups and hopefully shed some light on what you see ! Don't know if all this is relevant or not but here is the gun and the load.
Tikka tac a1 t3x 6.5 CM using a factory barrel suppressed
My load is 41.2 gn of H4350 with 143 gn hornady eldx bullet. I wont bore you with anymore unless needed.

Exclude # 1....I goofed that string up
3 shot groups
View attachment 8169902View attachment 8169903View attachment 8169904

For a 6.5 CR, you're .003 increments are just right. Any more than that would make your targets hard to read where one would easily not see and skip over an accuracy "node" or just get lucky to see it. Anyway, I can see the sine curve that I look for in my targets and I look at the top and/or the bottom of the sine curve where the groups have small vertical dispersion (like I see in #2). I would take a close look at seating depth from #6 to #8 and test just those again and some in-between them (like CBTO's in .001 increments from 2.276 through 2.270). Keep in mind that when you see something that looks good to you, you've always to retest to verify.

BTY, that's some pretty good results coming from a factory barrel, IMHO.

 

[4xtrak.chmp]

I would take a close look at seating depth from #6 to #8 and test just those again and some in-between them (like CBTO's in .001 increments from 2.276 through 2.270). Keep in mind that when you see something that looks good to you, you've always to retest to verify.

Next time i get to "play" in the reloading room thats exactly what i plan to do. Thanks for the help !