Need help with ES/SD spread

[brguide]

Okay guys. I have been reloading like bench rest guys. I have 2 custom built 6.5 Creedmoors. Both shoot under .25 at 100 yards and under .75 at 300 yards. I am VERY ANAL about reloading. I have spent thousands of dollars on the best of the best. My first CM can produce .25 or less groups at any yardage and has an ES of 10 and a SD of 3. I anneal after every firing, I use bushing dies, I ream primer pockets, I use Nosler cases, CCI-BR2 primers, H4350, and Berger VLD. I do not have any problem in my first build has a Shilen 6 groove 1:8 twist. My second rifle has a 4 groove ratchet 1:8 twist and this is the rifle I am having es/sd problems with.

I can shoot 1 hole groups with this gun have done the ocw test, seating depth test, ect. I found a great grouping load BUT my ES/SD starts out at 95 fps and ends up usually at 30 fps. But I can produce .75" groups at 300 yards. I have a V1 and V2 magnetospeed chrono. I have noticed a few things that may be the problem

1) Some of my primer pockets still feel really new I use the 21st centry primer to seat them. I usually go by feel and all primer pocket are reamed to .130 EVERY SINGLE ONE. but when I check the depth of the seated primer some are .003, .005, .0065. Could this be the problem?

2) Maybe I could have a bad batch of primers?

Could someone please tell me what would do this? I have tried 41.5, 41.6, 41.7, 41.8, 41.9, 42.0, 42.1, 42.2, 42.3. I use 42.0 because it is the best. Ocationally I get ES of 10 over 10 shots and I did not change anything. The next round could be 50 fps slower than normal and then even out again for 2 rounds then the next round be 40 fps faster than normal. What the heck is causing this? Only this I could think was maybe the primer are not seated all the way. I loaded up 10 round and made sure I set my priming tool so no matter what they all measure now .0065 depth.

Next question:

Why is it when I go out in the morning 27.00 station pressure, 48% humidity, 70 degrees i get velocities of 2788 fps but when I go out at 1:00 pm 27.00 station p, 48% humidity, 92 degrees i get 2830 fps? I have tested H4350 5 rounds in a plastic bag on ice and 5 rounds in the sun and got the same speed 2788? I am not letting them sit in the chamber too long either.

I have done over 2000 rounds of load development and testing total to numerous guns but this gun is the only one that is throwing the ES & SD crazy. I have never seen this. The last part different speeds at different times happens to every gun I have tested.

Here is a picture of 2 separate groups I can shoot these all day long.

 

[FearNoWind]

Wow!!! You've got it pretty well covered. The only thing I can think of is neck tension and whether or not you've tried turning your case necks, sizing them, rounding them out with a good neck sizing mandrel and checking them for runout.
I might suggest that if you're printing consistently under .5 MOA on target (that's my personal standard) forget about the SD/ES and enjoy the shoot. You ain't never gonna get 'em all in one hole.

 

[brguide]

Thats the thing though I measure the thickness of all my cases and all are within .001 difference (.0135 to .0145), Next I use a bushing so tension is always the same they all feel exactly the same when seating, I have 0 runout on cases and worst case have .003 on loaded but I fix that to maintain .001 or less.

 

[toliver]

warmer air provides less resistance.

 

[trigger puller]

The only thing I would check is neck tension but you covered that, you might check the crown and see if the powder marks are even thats just a WAG. Good luck

 

[Pdvdh]

brguide,
Different speeds at different times is a puzzler. You did identify different temperatures. Even if you kept your ammo the same temperature, the barrel/bore would be a different temperature. Perhaps the differing barrel temperatures are affecting bullet velocity?

 

[brguide]

brguide,
Different speeds at different times is a puzzler. You did identify different temperatures. Even if you kept your ammo the same temperature, the barrel/bore would be a different temperature. Perhaps the differing barrel temperatures are affecting bullet velocity?

Okay so I tried this also.
I shot the gun in the morning and got my 2788. In the evening with the gun in ac all day took out to the rang in the ac car slapped on the chrono and still it read 2830. So barrel was cold on both occasions? This is where it gets me. I can come back in the morning and shoot 2788 even after 30 rounds and the barrel is warm still 2788. LOL. Trust me I sometimes don't understand. I really don't think the temperature is doing this. Not that much of a climb. Could it be the chrono reading that but it really is not that speed? Has anyone else tried this with a bonified load they have and the magnetospeed?

Anyways I don't get all this I think its the chrono. But I can hook it up to my other gun and bam 10 fps in all 30 rounds.

 

[Pdvdh]

Okay so I tried this also.
I shot the gun in the morning and got my 2788. In the evening with the gun in ac all day took out to the range in the ac car, slapped on the chrono and still it read 2830. So barrel was cold on both occasions? This is where it gets me. I can come back in the morning and shoot 2788 even after 30 rounds and the barrel is warm still 2788. LOL. Trust me I sometimes don't understand.

Here's a thought. Don't go out on a morning shooting. Make your first chrono effort an afternoon shooting event. See if your MagnetoSpeed knows the difference between AM and PM...

 

[brguide]

Here's a thought. Don't go out on a morning shooting. Make your first chrono effort an afternoon shooting event. See if your MagnetoSpeed knows the difference between AM and PM...

Already tried that too...LMAO. I am just about ready to say screw it. She shoots great so I guess I will just shoot her now. I will take her out to 500, 700, and a 1000 this weekend and see if I have any misses high or low. If I don't then I know something is up with the mounting of the chrono. Because the chrono works great on all my other guns.

 

[MagnumManiac]

The difference in velocity between times is most likely caused by differing air density.
Do you shoot this rifle past 300yrds?
If not, your .75" groups at that range are pretty good, so your velocity changes aren't hampering your accuracy.
Before I even owned a chronograph, I had loads that were super accurate, the range really didn't matter either to about 600yrds. Then when I finally got myself a chrony, those same loads showed large ES/SD numbers, but shot great. I wouldn't use those loads at 1000yrds or beyond, but up to 600yrds they were very good. I think barrel time within a wide node is the cause of good accuracy even when velocities aren't within a neat 1-2% variation.
I think your looking into this too much, if it shoots great, why try to change it?

Cheers.
gun)

 

[brguide]

Found out what the problem was. It was the primers. I have 3000 primers all the same lot number but I decided to try another 1000 round box and sure enough those all shot within 11 fps ES. So the primers are just bad.

 

[Pdvdh]

I see you're in Arizona. How old were the primers, and were they exposed to high temperatures or moisture during storage?

 

[brguide]

Not in my storage. But before I got them who knows. I store them all in a seal tight 20 mm ammo box.