Neck tension (continued) and other considerations

[John Weigel]

After the recent discussion about neck-lubes and neck tension issues, I decided to check my earlier conclusion that it doesn't make a lot of difference on target. Of possible interest to other rabbit-holers, I share attached target from yesterday's practice, as I similarly tested a couple of other things. None of the conclusions I draw are statistically valid due to small sample size and three-shot groups, but at least hint at some interesting possibilities. Here is a brief explanation of the info on target. All shot with 7 SAUM, mostly to finalise tuner setting pre Belmont (Cortina parallel).

1.Neck size does matter. Despite reasonably safe conclusion that my load is pretty good, when I shot a six-round test (Target 11) at best tuner setting with 3 'loose' (ave 12 thou neck wall thickness, and noticeably 'easy' to mandrel) and 3 x 'tight' (ave about 13 thou walls, and mildly more resistant to mandrel and seating) to get an indication of validation. I loaded these cases along with the others shot on the day, all together, with same processes and materials. All cases were third-time-fired, these varying fairly equally from my 12.5 targeted neck wall thickness, and kept all other factors consistent with the other rounds shot on the day (using relatively slow MEM 7538 2209 powder), the result was a train wreck on target. I thought it important to reveal this unscientific indicator after shooting my mouth off previously about minimal impact of such variation in neck tension.
2. Oil in barrel. I reaffirmed with first shot velocity in cold barrel post-clean-to-bare-metal (as per my five-minute secret blend of Sweets and IOOSO abrasive that I posted previously about) that velocity of that first shot reaches much closer to second and third shot velocities when a thin film of gun oil is patched into barrel after cleaning. With the two-only sighter dilemma, this may be of interest to some.
3. Main purpose of this practice was to narrow down best tuner setting for my load. But since my latest batch of 2209 (MEM 7538) is about gone, I shot a couple of groups with more recently purchased powder (MEM 7571) See Target 8 and Target 14. The speed difference was frightening at the time, though the target seemed to like the change. I've never shot in the 2920s or 30s before for fear of shortening brass life, yet saw no signs of heavy bolt lift or impression in case head. I deprived and test-primed, and primer-seating tension seems to be OK. Guess I'll stick with the new speeds, though I'll bet that if ammo is warmer, I'll need to back off on the current 54.9gr load. The variation in 2209 quality always astounds me, as does the terrible ES scores typical for this powder in even small sample sizes, but I still seem to have better results than I do with 2213SC. Gotta get me some of that N555 that the rest of the world loves.
4. I've experimented extensively in the past with variations in ammo temperature, and am confident that all issues of range temps, humidity and position of the moon are irrelevant, but will post my data one day here if there is interest. I wanted to get ammo test at 30+C, but it had cooled to much less than that in test on Target 13, probably about 26-28. Group seemed to open up, but I can't really say for sure without a better test, which I'll do soon.
5. I accidentally sized a bunch of brass a few thous short of usual, which aims to allow 2 thou play in chamber; these were shot at Target 12, and I'm happy to use these going forward. FWIW, in the past, when I have struck a round with not enough shoulder bump, and bolt closure is heavy, I've seen no problems on target.

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[PeteFox]

Dare I say it John, that you have 2 variables in play. How do attribue the outcomes between the two?

Maybe a different neck tension requires a different tuner setting. Just saying

When the neck tension is optimal it will show on target, tuner tweaking aside. However you do have runs on the board, so something is working for you.
Pete

[John Weigel]

Hi Pete. and thanks.

"Maybe a different neck tension requires a different tuner setting. Just saying"

Sure, you may be right - it's an interesting thought. But what (at least) the bad group on Target 11 warns me of, is that at a given tune, to be more careful about neck tension consistency than I've been in the past. Not anywhere near a proper test, granted!

[wsftr]

Its interesting as Erik C states that neck tension doesn't matter it just needs to be consistent. He consequently only makes two mandrel sizes.
So many variations and results - I love ETs, Garmin chronys and club days - so much data to be gathered.

looking at the target I do wonder if you should be considering POI stability rather than group size - or maybe I am miss understanding.