Lets take a look at this theory....
"If a powder shoots accurate loads at 4.0 grains, and all the way to 4.3 grains shoots accurately, and also, all the loads are hitting near the same location...does that mean mixed brass with different case capacities can be pretty accurate too?"
Well, we are going to find out!  We took 5 popular brass manufacturers, a proven accurate load from 4.0-4.3 grains, same primers, same match gun, same weight bullets..and did some testing..
So here is a theory...you find a load range...with this powder, its between 4.0-4.3 and the bullets in this range hit a similar spot and all measures between 4.0-4.3 group well, near this spot. 

So, essentially, if you use mixed brass, that is very similar to varied powder loads in that if offers variable pressures. A case with 14.2 grains capacity will offer lower velocity, simulating say a ~4 grain load, and a case that is say, 13.0 grains capacity will simulate a load of say...~4.2 grains of powder...

So the theory is...if loads from 4.0-4.3 hit near same area, and group well, then using mixed brass that offer a range of case capacities producing different pressures should as well.

Lets see if our theory has any validity.

PPU brass
We threw this new brass into the test, but it doesn't belong in there.  Why?  Because this batch of new PPU (PRVI) brass so was incredibly stiff, we could not even flare the brass at all before seating the bullets.  The brass would get STUCK on the flaring stem.  THEN, after that, we could not even seat 1 bullet to 1.095 like everything else, it would only go down to about 1.105 to 1.115 before the seating stem would be under so much pressure, it starting digging into the copper jacket of the bullet itself.  And the sound the Dillon 550B made when trying to seat the bullets into this batch of brass was crazy.  It took so much pressure on the hydraulic press to seat these bullets.  So what are we leading up to saying here?  NECK TENSION on these loads, this group below was OFF THE CHART.  SUPER HIGH NECK TENSION.  Super high.  And guess what everyone already knows?  Variable and super high neck tension simply doesn't work for accuracy.  Its terrible.  We use a lot of PPU brass, its only this one batch that is like this, not all of it. 
PPU Prvi P. Brand New Brass
High neck tension is not good for accuracy.
PPU Prvi P. Brand New Brass
See the ring around near the tip?  The brass was so stiff, the bullet would not press all the way in, so the seating step left heavy mark in the bullet..
On to the testing...
Test parameters...
  • The "branded" brass was weighed to be within .02 grains of each other
  • The brass all had same length
  • Federal Gold Medal primers in all
  • All Precision Delta HP 124 grain bullets weighed from 124.02 to 124.04 grains each.
  • Powder load precision was from 4.12 to 4.10 grains using Gempro 250
  • Mixed brass was picked purposefully, with large variance in weights picked.  Each batch contained a extreme spread in weight of minimum 5 grains. 
    So some group was from 65-58 grain weight, another was 58-64, then 58-63, etc.
  • Mixed brass and branded brass was measured with water, to determine internal case capacity
WIN brass
All this brass had internal case capacity of ~13.9 grains
Xtreme brass
All this brass had internal case capacity of ~13.0 grains
Starline Nickel brass
All this brass had internal case capacity of ~13.7 grains
Hornady brass
All this brass had internal case capacity of ~14.2 grains
Mixed Brass #1

Mixed Brass #2

Mixed Brass #3

Mixed Brass #4

Mixed Brass #5  The "Mangled" bullet test
Since it was our theory, that mixed brass would produce similar accuracy results IF the powder in a certain range was accurate and hit near same spot....we decided to deform and mangle the bullet tips and ogive area to show that this doesn't matter that much for pistol shooting because its not impacted by wind drag and coefficient of friction like rifle bullets are. A pistol can stabilize and shoot accurately a bullet with a dented, or scared tip, as long as that bullet is the same "kind and weight" as the others.  Is this theory correlated by evidence?  Well, in this 10 group test, using 5 bullets each, this group of mangled bullets happened to be the most accurate.  It won't every time, but in this case, it did.  This is not PROOF that mangled up bullets are going to shoot lights out groups, however it is supporting evidence that with pistols at 10 yards, it doesn't matter near as much as with rifles at 100 yards...  Pistols are vastly different in that airflow/atmospheric conditions, and aerodynamics, drag, all that, don't matter at close range.  
We took screwdriver to one..
Dented the top up pretty well with hammer and screwdriver...sledge hammer actually..
Took a pliers to next 3..
Made the tip of the 2nd one square by crushing it with pliers...then the 3rd one, one on fight..we took pliers and totally made it "oval" and out of round..
We then shot the group....marked each shot as we made them
The Mangled Group..
#1 was screwdriver
#2 was pliers made into square
#3 was pliers made out of round (ogive tip only, not brass part...)
#4 was pliers marks all over it
#5 was screwdriver slotted into just 1 side of the HP

That is 10 yards..5 shots...
Standard Deviation got cut off
SD = 9
ES = 21
LOOK!! We have a correlation!
The 4.1 IMR TARGET in middle area means "4.1 grains of IMR TARGET".
The brass with the highest internal volume was the lowest velocity, because it was lowest pressure?  The brass with the lowest internal volume was the highest velocity, because it was the highest pressure.  And look?  The mixed brass, which we purposefully had a large range of low capacity and high capacity cases?  landed right near the middle generally.  Right where it should be. 
So...what is the take away?  If you need more case capacity because the powder you are using is bulky and you worry about too high of pressure?  Get some brass that has very high case capacity, it will help!  If you are shooting lower power rounds, then just get any brass.
What is the other takeaway from this entire page?

If you find a powder, like we did, in IMR Target, that shoots good groups across a range of loads near each other....and they hit generally the same area of the paper at say..10 yards...then mixed brass can work very well.

But what if your powder doesn't group well across this range of near loads?  Is mixed brass terrible?  Don't even think about it...we have that test too...its coming! 
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