Which Rabbit Hole should I go Down.(Velocity Variation) {UPDATE}

[JPB4BAMA]

I chose to follow the Rabbit down the Primer Weight Hole.
I weigh sorted 2 sleeves of Rem 9-1/2 into bins of 0.04gr, and saw a beautiful normal distribution centered between 5.23 and 5.27 grains. The tails contained 8 each > 0.08 gr and < -0.08 from the mean.

Selecting 20 rounds from the Mean batch loaded with 49.2 gr H4350, 20 thou off
Mean 2753
Stdev 6.98
Range (ES) 24

Five (5) from the heavy Primers
Mean 2777
Stdev 4.4
Range 12

Five (5) from the Light Primers
Mean 2735
Stdev 5.7
Range 15

Total Range Test of 30 rounds
Mean 2754
Stdev 15.3
Range 63

Note - NONE of the Heavy or Light primer shots fell within the entire range of the group of 20 from the mean group, its like 3 different distributions, and the 20 round group is very similar to what I was experiencing in the past, although previous sample sizes were quite a bit larger, and anomalies were buried in the bulk of large groups and any misses on target I just blame on myself or wind.

Now for the Statistics Guys, It may not be a big enough sample size for you, but in a system as complex as internal ballistics, a single variable change that shows this behaviour is real, certainly not the whole picture but real none the less.

 

[JPB4BAMA]

How is your neck clearance? Not just on a sample of one or two cases. Check a bunch.

Fifty rounds fired today in a test of weighing primers (plus a comaprison of 3 different brands) The fired neck minus the loaded neck in 0.005 (+/- .001) within my capability to measure with a caliper, but anyway it is consistent and I would certainly hope enough?

 

[v63800]

I'm going to assume that I measure fired case necks and compare them to loaded cartridge necks?
If so I will do that once I get the next batch loaded and fired. On that note, I already know that the Peterson necks are thicker by a touch over .001 to 0.0015, however on the virgin brass as well as the small die sized I don't feel any on chambering that indicates any resistance, but It's probably well worth the test.

Check your neck clearance, i had to neck turn Peterson brass and the new Lapua 284 brass to fit my chamber. what neck size is your Reamer. small base die won't help you here. Measure your loaded rounds with a quality micrometer not calipers to confirm.

 

[coford]

Two suggestions and a comment.
#1 Take the barrel off and use a pin gauge to determine the "real" neck diameter. Reamers and prints can vary from reality.

#2 Make sure you are not having a problem with overall length. The Peterson brass I have used is always longer than Lapua. The best way to really check is to insert a case in the chamber, close the bolt, and look at the chamber with a borescope from the muzzle end. It will show you how much clearance you have for overall length.

Comments - Sorting primers works - don't believe the critics. If 50.5 grains to 51.0 grains of 4350 at .020 off the lands doesn't shoot then something is wrong. I have been through 11 barrels with the .284 and it is a very forgiving cartridge - if you feed it what it likes. YMMV

 

[JFrank]

I'm pretty sure of neck tension, although maybe a bit low. I'm measuring 0.001 to 0.0015 and the seating force is really consistent on this 1X brass at 20-25 # as measured on the K&M arbor press (Not Hydraulic),
As for case volume I did a random sample prior to loading and it was really consistent, however unfortunately my ammo box tipped over on the way home from the range so the ones I had noted as outliers are all mixed up now, so that will have to wait till the next trip.

incorrect neck tension ( bullet hold ) can ruin your day and skew all your test results, if you have time then run a bushing test, I started using a charge ladder format to see the load coming into tune, as little as .001 in bushing size can make a huge difference.
You can do the same test with primers.

 

[J_idaho]

I chose to follow the Rabbit down the Primer Weight Hole.
I weigh sorted 2 sleeves of Rem 9-1/2 into bins of 0.04gr, and saw a beautiful normal distribution centered between 5.23 and 5.27 grains. The tails contained 8 each > 0.08 gr and < -0.08 from the mean.

Selecting 20 rounds from the Mean batch loaded with 49.2 gr H4350, 20 thou off
Mean 2753
Stdev 6.98
Range (ES) 24

Five (5) from the heavy Primers
Mean 2777
Stdev 4.4
Range 12

Five (5) from the Light Primers
Mean 2735
Stdev 5.7
Range 15

Total Range Test of 30 rounds
Mean 2754
Stdev 15.3
Range 63

Note - NONE of the Heavy or Light primer shots fell within the entire range of the group of 20 from the mean group, its like 3 different distributions, and the 20 round group is very similar to what I was experiencing in the past, although previous sample sizes were quite a bit larger, and anomalies were buried in the bulk of large groups and any misses on target I just blame on myself or wind.

Now for the Statistics Guys, It may not be a big enough sample size for you, but in a system as complex as internal ballistics, a single variable change that shows this behaviour is real, certainly not the whole picture but real none the less.

Congratulations and thanks for testing a crappy primer now I know not to buy that primer

 

[JPB4BAMA]

Two suggestions and a comment.
#1 Take the barrel off and use a pin gauge to determine the "real" neck diameter. Reamers and prints can vary from reality.

#2 Make sure you are not having a problem with overall length. The Peterson brass I have used is always longer than Lapua. The best way to really check is to insert a case in the chamber, close the bolt, and look at the chamber with a borescope from the muzzle end. It will show you how much clearance you have for overall length.

Comments - Sorting primers works - don't believe the critics. If 50.5 grains to 51.0 grains of 4350 at .020 off the lands doesn't shoot then something is wrong. I have been through 11 barrels with the .284 and it is a very forgiving cartridge - if you feed it what it likes. YMMV

I came up with the 49.2 because of the lower case volume of the Peterson Brass. According to Quickload, (and actual velocity data), it is right abut the same as 50.5 grains in a Lapua case.
After sorting the primers and upping the neck tension by about 0.001 it seems that the velocity is under control as far as SD is concerned. BUT the groups are crap so I have more work to do there.