I am loading for a 3oo winmag and have used W-W and Norma brass. I was chronographing the load this weekend and found that the W-W loads were 50fps faster as well as having a better standard deviation. All elements of the load are identical except for the brass. Any of you run into this? I am used to powder/bullets/primers having an effect but I have never really paid too much attention to brass from the primary sources.

I have found that in general the WW cases, for larger center-fires, seem to have a wee bit more case capacity, and if I'm looking to move it out fast they are the ones I use.

Haven't had any experience where the amount of powder remained unchanged and difference was noted due to the cases.

Surely could have happened and I simply chalked it up to reloading variances created by me.

I'm speculating here:
I would suspect that the WW cases have smaller capacity than the Norma brass, for the same powder charge in a smaller volume, pressure would go up.
The neck tension on the bullet may also be a factor, this may be an explanation for the smaller SD as well.

The difference is likely not in case capacity (the WW would usually be greater than Norma, which would tend to lower velocities, all things being equal.) My best guess is that the difference in anneal/neck thickness/bullet pull is probably the contributing factor in the velocity differential.

Is one new and the other previously fired?

The brass was virgin. I ran all cases through the resizing die (Forster BenchRest). I agree that something with the Winchester is boosting pressure or the Norma is reducing pressure. Neck pressure could be the issue as well as case capacity. At any rate there is always operator error to consider. By the way average velocities (180gr TSX) were Norman- 3002fps W-W- 3053fps.

Could be either the tension or the volume, could be any factor related to the brass.

In a .308 load I worked up, 44 grains of RL15, and a WLR primer with a 150 SMK gave me 2798 fps with Lake City Brass. The same load with Cavim brass is 2725. Both cases were once fired from the same rifle. Same component lots except the brass.

I had exactly the same results when loading for a 7mm Rem Mag. The exact same load in Norma cases gave 50-60 fps less velocity than the same loads in W-W brass.

I also noted a big difference in performance when comparing Remington and Weatherby brass in my 300 Weatherby Magnum. The Remington brass has less capacity than the Weatherby. To get the SAME velocity I have to use 1.5 grains less powder in the Remington brass.

How many shots, and what was your standard deviation?

Depending on your sample size, 50 fps might not be statistically significant at this level.

But to give a more general answer, yes, changing brass changes the load. 100 fps difference due to a change in brass is not unusual.

Thanks for the replies. I might massage the Norma powder weight or maybe just leave it alone. I don't believe 50fps is going to make that much difference and I seldom shoot out to 300 yds. much less past that range.

Norma brass has a reputation for having more internal capacity than other makes.

In the 30.06 the average overflow capacity for my norma brass is 71.9 grains of h20 whereas Remington is closer to 69.2 grains.

Therefore I would expect the norma to show lower velocity than the other make, assuming the same holds.

The higher ES might be cured by a small increase in charge, it would be interesting for the sake of experiment to drop the charge in the other brass a bit to see if you can replicate the condition.

If so then it's a the capacity, if not it may be some other issue as Stonecreek alludes to.

quote:

Originally posted by msc:
The brass was virgin. I ran all cases through the resizing die (Forster BenchRest). I agree that something with the Winchester is boosting pressure or the Norma is reducing pressure. Neck pressure could be the issue as well as case capacity. At any rate there is always operator error to consider. By the way average velocities (180gr TSX) were Norman- 3002fps W-W- 3053fps.

It takes upwards of 7,000 psi to expand the case to seal the chamber. Wahtever the amount needed takes away from the amount of pressure to push the bullets. Hence a case with softer or thinner case walls (sounds like the Winchester cases) will expand with less psi and thus more psi is available to push the bullets. While I've measured this numerous times with pressures it also is a measureable effect with a chronograph.

Use cases from the same lot that have been once fired. Using a 10 shot test string (5 shots may not be a large enough sample) NS 10 cases and FL size 10 cases. Use the same load in in each. Then chronograph letting at least 1 full minute go by between shots. Let the barrel get stone cold between test strings. Compare the average velocities, the SDs and the ES. Most often the NS'd cases will give higher velocity with smaller SD and ES.

We want to think the NS cases have a larger internal volume (they do) and there fore the psi and fps will be lower. Doesn't always work out that way. This is because less work is done by the available gas pressure to expand the case and is used to push the bullet.

Larry Gibson

quote:

Originally posted by Larry Gibson:
It takes upwards of 7,000 psi to expand the case to seal the chamber. Wahtever the amount needed takes away from the amount of pressure to push the bullets. Hence a case with softer or thinner case walls (sounds like the Winchester cases) will expand with less psi and thus more psi is available to push the bullets.

The pressure will be (as near as makes no difference) the same on the case as it is on the base of the bullet. It could be viewed as acting in an outwards direction, in every direction, from the centre of the case. PSI that might be used to push the bullet is not used up expanding the case, though energy will be.

Ah, you caught me in a matter of semantics.....energy it is.

Larry Gibson

It's quite easy to tell which case has more/less capacity, simply weigh one of each with a spent primer in place and before you size them, and then fill with water to the top of the neck and weigh again, whichever is heavier has more capacity than the other.
I will bet that the Norma brass has a lot more capacity than the Winnie brass, at least that has been my experience.
My own loads in Norma brass have run as much as 5gr's heavier than other brass simply due to the increased capacity.

Cheers.

Everything being equal it is case capacity. Just weigh the brass with spent primer and water like detailed above. Different brands of brass have different internal volume capacity.
Believe me, I have been through this. Even different lots of the same brand may vary.
Jim

Again I appreciate the replies. I did a little checking and the difference at 400 yds is 3/4" in drop and a loss of 75 foot pounds of energy. My interest in equalizing the loads is severely diminished.
Thanks.

As Antelope sniper mentioned- what are the numbers? ES, SD?

Also, do the test again, same way. See if it stays the ways it was the first time.

Often, interesting but inconclusive results are seen when doing small lot sampling (under 20 or so shots)- basically, a controlled 20 shot , shaded ammo/bullet/timed fire with warm up shots over a covered and artificially lit chrono will get closer to the truth, but repeatability is key. Do it over a few times and see what the outcome is.

As an expample, I shoot high power with an AR15 (service rifle) and a known accurate load of varget and LC09 brass with CCI 450s and Hornady 75 BTHPs will shoot to 2625 fps in one session, then a few days later, ammo from the same production lot (same headstamp brass, same box of primers/powder/bullets etc) will shoot at 2598 for a 20 shot average. SDs will vary from 12 to 25 and ES from 35 to 65.

Sorting them by loaded weight reduces variation somewhat, but not enough to matter at 200 and 300 yards in High Power Competition, all will hold the X ring if I do my part.

Going to 600, using 80 Amaxs and more varget, in same lot remmy cases, I strive for loads that average under 15 fps SD and like to see 25 or under ES.... Velocity I could care less about-its only paper I need to penetrate (and they go faster than the 75s BTW, since they are loaded long and use more varget...)pressure signs are the "uh oh" indicator.

Finaly, like youstated- virtually nill drop and KE difference, all within "Minute of Deer" or whatever critter you shoot at, so no issue-as long as POI is same....