Take a stab at what you think happened here.....

[Hotolds442]

WOW!!!

Ive done a ton of primer testing in my 260 and 300wm because i read so much on primers and primer seating and the difference in primer brands,cup hardness hottest and coldest ect and can say that ive seen vertical spread but never that bad.
What was the temp when you fired those rounds?

Also youve been talking to Dean havent you lol!

Temperature was around 60 degrees, and Dean's suggestion was responsible for this little experiment. Hardly the outcome I expected though.

[Hotolds442]

If case prep was same that means its nothing to do with the brass... bullets all the same...powder the same... maybe seating depth or has someone said that already? Maybe different primer/lot of primers like DanSavage mentioned? Or is it something external to the mechanicals; with a vertical like that could be breath control/not firing during natural respiratory pause

Oh hell just tell us already
If it were something like breath control or trigger control you'd expect the horizontal would be wider than the vertical, or that's what I've seen with newbs learning to control a rifle for precision. The horizontal spread was .295", about average for the rifle. When I first shot the string, I had forgotten about the primer swap, and had a real WTF moment. A loose reticle would have been off in both axis, horizontal and vertical. I ran a card between barrel and stock, checked all the screws and bolts, did many of the things suggested here. I thought about it for quite a while, frustration had set in, I even shot my 243AI to make sure it wasn't me although I felt good about shot placement on each and every shot. And then I noticed the tag on the MTM box. Bold letters. CCI-200.

[LongRange]

Temperature was around 60 degrees, and Dean's suggestion was responsible for this little experiment. Hardly the outcome I expected though.


I knew he was behind this.

Like i said i did a lot of primer testing a few years ago and learned a lot from it but never seen that much vertical....this should be a sticky so ppl can see how much of an effect primers have.

[DanSavage]

Well they say,,use the most gentle primer that will reliably ignite the powder. So I guess you won't be sticking with the 200's lol.

[Texas10]

Hotolds442,

How long did the round dwell in the chamber before shooting? In your opinion, is it the powder that is changing it's burn rate with temperature or the primer that is changing?

I seem to have a similar problem with IMR30301 in my 223, and figured it was the powder charge. Never considered the CCI400 primer, but did recently switch to WSR primers.

[Hotolds442]

Well they say,,use the most gentle primer that will reliably ignite the powder. So I guess you won't be sticking with the 200's lol.
I shoot CCI pretty much exclusively, using the old school method of magnum primers in magnums and standard primers in non-magnums with a substitution of magnum primers in non-magnums when using ball powder. This is the first time I've experimented and probably won't try it again. The WSM's will see a steady diet of CCI-250's in the future.

[Hotolds442]

Hotolds442,

How long did the round dwell in the chamber before shooting? In your opinion, is it the powder that is changing it's burn rate with temperature or the primer that is changing?

I seem to have a similar problem with IMR30301 in my 223, and figured it was the powder charge. Never considered the CCI400 primer, but did recently switch to WSR primers.

The rounds were in the chamber for less than 30 seconds each. Just guessing, I'd say that the chamber temperature increased with each shot, and that temperature transferred to the powder enough to change the ignition characteristics of each progressive round, but again, that's just speculation. I wish I had a pressure trace I'd do this test again. There's a used one for sale locally at a good price but right now I just can't justify it.

[sharpshooter]

I could see that primers could affect the way the powder column burns, but I not really buying into the idea that the powder temperature is that sensitive to get the optimum results. Typically ignition issues happen at low temperatures, especially with ball powder. If the ambient temperature was in the 60's, I would imagine the barrel had to be about 90-100 degrees after 4 shots. I just can't see an additional 30-40 degrees in this temperature range affecting the velocity that much.
Proof positive would be if you ran this test again and recorded the temperature of the chamber after each shot until the group returned, while chronographing. Or, do the test again on a very hot day and see if it grouped right off the bat.
I've had stranger things happen.....

[scooterf79]

Wow! Very interesting thread. I wouldn't have imagined that much of a difference. Interesting test Dan. Deano will probably chime in sooner or later, I wonder if he had anything similar to this. I remember the thread the other day when this was brought up. Ill be keeping up with this one.
Scooter

[darkker]

There's a used one for sale locally at a good price but right now I just can't justify it.
Don't let it get away, you'll regret it:cool: