Good info for reloaders, An experiment I did.

[cfvickers]

I just finished running some tests with what would be the effects on group size and point of impact when using one randomly selected brand of brass against Federal brass. I will call the federal brass my control, reason is that with my american designed cartridges it consistently turns out the very best groups with any given rifle I have tried. For the 6.5x55 I used Norma against Remington, and the 6.5-284 I used Lapua against Winchester as that is all I have. This is not overly scientific as I only shot one 3 shot group with each brand in each caliber but the results were fairly consistent in that it does effect group size significantly in the .300 win mag, 25-06, 7mm-08 and the 6.5-284 Norma. I tested it with the 6.5x55 and the difference was not as large.

Point of impact was even more troubling with some, less with others. The 6.5-284 was the most consistent, followed by the 300 win mag and 6.5x55.
For each rifle I loaded a known good load with which I had well documented results on several occasions.

So here is what I got.
25-06 Encore Rifle:
Federal Brass, .49" 1"low
Winchester Brass, .91" 2" right, 1" low

.300 Win Mag Model 700 Stainless:
Federal Nickel brass: 1.1" 3.25" high
Frontier Brass: .61", 3.25" high, 1" left

7mm-08 Scrap Metal rifle with nice walnut (kimber)
Federal Brass 1.21", 1.25" low 1.5" right
Remington Brass 1.70", 4"low

6.5-284 Husquvarna Crown Grade Rechambered from 6.5x55
Lapua Brass .55" center
Winchester Brass .95" center

6.5x55 Steyr SBS Mountain Stainless
Norma Brass .85" center
Remington Brass 1.00" .75" low .5" left

As you can see the group size with various brass stayed within hunting accuracy limits, but the point of impact (center of the group) changed with most changes in the brand of cases. The 7mm-08 changed radically enough to possibly cause a miss or a crippled deer at ranges beyond about 150 yards. I did this test to prove a point to my dad who often brings me 5 different kinds of brass for a rifle and tells me to load it for him or tells me I knew you could use some 25-06 brass or whatever. Rather than act unappreciative of his efforts I thought I would show him how big the differences are. Also because he didn't want to spring for a bag of Federal 7mm-08 brass but wanted me to work up a reliable load that shoots under an inch for it. His excuse was that I already have a bunch of 7-08 brass, now he understands.

I hope that it will be helpful to someone.

Cody

[whelenman]

It would be interesting to see the variations in velocity from case to case along with your findings. Would the big variation seen with the 7-08 correspond with a larger variation in velocity? Any time you vary the case capacity and thus the velocity of a load you change the harmonics in the barrel and perhaps change the point in the node that the bullet exits the barrel is my understanding. Could it be that the initial loads in the Federal Cases were worked up to correspond with different points in the node and just by chance the 7/08 hit the highs and lows of the node because of the variations in case capacity and velocity? I'm not sure I put this well but that's what I was thinking about.

Doesn't it irritate you to have someone ask you to reload some ammo for them to only be given sub par components which means your loads will be sub par. I just had a guy give me some crimped Lithuanean brass to load for his .308 that I'm putting together as a favor. I don't have a good feeling about it. He's trying to save $20 in the wrong place.

[cfvickers]

That 7mm-08 is horribly finnicky. You may be right about the nodes. I worked all of the loads up, and that particular one I worked up using remington brass. I have to go to a friends house on the right day to use a chrono so I didn't get to check velocities. I will have one in a couple weeks though and may redo this test.

If the brass is NNY stamped it isn't bad stuff but Fed or Frontier is better. In the 25-06 NNY brass is better than remington, and lasts a decent time. But you are right. There is no substitution for good components, what drives me crazy is when I ham handed 6 different kinds of brass and they want a load that will shoot sub moa. Not happening.

[youp50]

Interesting stuff, thanks.

Are all brass trimmed to the same length?

[cfvickers]

yes.

[dannoboone]

There's something else ya might try. Some of the long range guys
have been filling up fire formed cases (out of the same rifle) with very
fine powder, and pouring it from one to another case to see how
equally they fill. They reason that it makes more sense to find the
capacity of each case than to weigh cases.

I tried their method last year for a .25-06 with many scrounged
cases, some previously .30-06 & .270 sized down to .257. They
were all fire formed out of the same rifle. To my surprise and
amazement, not all of the original .25-06 cases FROM THE SAME
LOT held within a 1/16" of powder filled up into the neck (Remington),
while some of the previous .270 Fed and .30-06 Rem cases matched
the .25-06 Rem case volumes.

I should say that all cases had been trimmed, annealed, neck
sized and primed prior to volume measuring (and all had been
previously shot in the same rifle). Those with equal volumes within
1/16" got loaded up with 54.5gr RL17 and Nosler 85gr BTBT's.
At a couple 5/16" groups, the Savage 112 got the best groups
it has to date, but further experimentation is certainly warranted,
here. I need to know if that was just a fluke, or if there is
more justification in volume measuring vs. weighing, and if this
makes more a difference than the type of brass used. I know
that brass companies cannot possibly use the exact same
alloys, which should make a difference in neck tensions.

[Richard]

From a both long and short range benchrest shooter, here is my take on your delima.............A host of things ;D

As was mentioned, brass from different manufacturers can have a notable difference in weight. The same can be said of brass from the same manufacturer if it comes from from a different lot. The point here is that when you re size your brass, the outside of all cases will be the same...................however, because of the varying weights, the internal dimensions are different. Hence, the same amount of powder in different cases will produce different pressure/velocity/barrel harmonics/point of impact!

Different makes of brass will have a different composition which make some softer and some harder and others in between. Hardness or elasticity will have an effect on neck tension. Also, the number of re loadings can cause brass to "work harden" which will cause differences in neck tension.

When it comes to neck tension here is another "fly in the ointment!" Brass wall thickness (more specifically concerning the necks) can have a lot of variation. To measure this, we use a "ball or tubing" micrometer that reads to the ten thousandths of an inch .0000". Much of your typical Win, Rem, Fed brass can have neck wall thickness vary (when measured around the circumference of the neck) of 3 to 4 thousandths. You might get one brand/lot that the wall will mic .013" on one side and .016" on the other etc. Then you get another brand/lot and the wall is .014 to .018"? Well, the later will put more neck tension on the bullet than the former. Besides that, your bullet will not be centered in the case since sizing transfers and difference to the interior. Coupled with the fact that factory chambers are notoriously loose (they have to be in order to shoot all this brass with different size neck walls), the case if roaming all over the chamber. You know that little spring loaded plunger that helps push your case to the side so it comes out the ejection port??? Well that is also pushing against the case in that loose chamber and forcing the neck and bullet to one side. Bullets do not straighten out in the throat when fired. They in-fact, enter the bore "crooked..........and the exit crooked and out of balance from going down the bore that way.

If you buy quality brass such as Lapua or Norma, you will generally not encounter a lot of these problems. When neck wall thickness differs, the solution is to "turn" them. A mini piloted hand lathe cuts the thick side to match the thin side and makes the walls all the same thickness. This however causes another problem in factory chambers.............now the neck is really loose. In custom chambers you decide what you want the neck wall thickness to be and turn all your brass to that dimension...........then you have your gunsmith order a reamer to cut your chamber so those "turned" necks fit your gun precisely with maybe only .001" on either side. Then you only neck size (most of the time) or use a full length "bushing" neck die so you squeeze the neck to the precise size for a proper bullet fit............you don't use that nasty expander ball to double work your brass. Then, after a few firings, you anneal the necks so the brass keep the same tension on your bullet.

That's why you are experiencing those big differences in groups size and POI shift!
Richard