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From: bartb@fc.hp.com (Bart Bobbitt)
Subject: Testing .308 Win. Handloads
Organization: Hewlett-Packard Fort Collins Site

In January, 1995, New Zealand hosts the International Palma Matches.
Their national shooting organization will provide .308 Win. ammunition
loaded with the following components:

  * Winchester case, weight about 166 +/- 2 grains.

  * Winchester WLR primer.

  * Sierra 155-gr. Palma Match bullet seated to OAL of 2.800 +/- .002-in.
    30 pounds of seating pressure used.

  * 45.3 grains of Hodgdon H4895 (Australian manufacture).

Having assembled some of this stuff, I tested it for velocity data in two
different barrels.  Rounds were fired every 60 seconds; bolt closed on
chambered round 15 seconds before shooting it.  Four very interesting
observations were made:

  * Both barrels had instrumental average velocity at 15 feet of about
    3032 fps; standard deviation of about 8 fps.

  * This is a maximum load for ambient temperatures of 55 to 60 degrees F.
    If used in warmer environments, it may start blowing primers.

  * Those standard large rifle primers were definitely the most uniform
    Winchester primers I've ever used.

  * During tests with the second barrel, I was able to predict velocity
    within 5 fps by noting how hard the rifle was held against my shoulder
    while shooting from a bench.

Regarding the Winchester primers, I haven't used any since the early 1970s.
They just didn't perform well enough to produce velocity standard deviations
of less than 12 fps; not quite good enough for best long range accuracy.
Well, if this particular lot (made in early 1993) is typical of what USRAC
is making these days, I'll feel great about getting two bricks of that same
lot of primers.  I was quite impressed.  I'm anxious to test that load
for accuracy at 1000 yards.  Although velocity was quite uniform, if the
primer's are too hot, they'll ignite the powder too fast which will cause
the pressure curve's front end to be steep/fast enough to slam the bullet
into the rifling too hard.  Probably hard enough to significantly
upset (deform) the bullet's back end that it won't shoot accurate.  At 100
yards, the load shot under half an inch, but I don't shoot very accuratly
from a benchrest.  And even a small amount of bullet unbalance will still
shoot about half-MOA groups at 100 yards, but at 1000, those same bullets
keep moving at right angles at an ever increasing amount per yard of
downrange travel that 2 to 3 MOA groups happen.

It's my benchrest technique that is the basis for the last observation.
I try to hold the rifle with the same buttplate pressure against my shoulder,
but I just don't.  With the rifle used for the second test series, I paid
extremely close attention to the pressure on my shoulder as I held the
rifle against it.   Here's the velocity numbers vs. shoulder pressure of
heavier (H), meduim (M) and lighter (L) amounts:

 1.  H  3045           10.  M  3033             19.  L  3023
 2.  H  3040           11.  M  3025             20.  L  3012
 3.  L  3013           12.  M  3038             21.  H  3049
 4.  M  3024           13.  M  3034             22.  M  3034
 5.  L  3022           14.  M  3037             23.  M  3026
 6.  M  3033           15.  M  3038             24.  M  3035
 7.  L  3019           16.  H  3040             25.  M  3032
 8.  L  3018           17.  L  3022             26.  M  3034
 9.  L  3023           18.  M  3039             27.  M  3035
                                                28.  H  3044

It was somewhat amusing that after firing a shot, I would tell the Oheler
chronograph operator whether the shot was going to be slower, average or
faster in velocity and estimate a range it would be in.  It took about
5 or 6 shots to get calibrated in relating shoulder pressure to approximate
velocity.  Had I not ran out of ammo after 28 shots, I could have kept that
scenerio up all night.

After eliminating those shots called faster or slower, the remaining 15
shots show suitable velocity control of about 14 fps spread.

Should a reader with excellent statistical analysis skills choose to
crunch these numbers to show any trendy things, have at it.  Please post
your findings so we can all benefit.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Reload Accuracy ?
Organization: Hewlett-Packard Fort Collins Site

mike@baobab.cadif.cornell.edu wrote:

: Which of the variables within a reloader's control have the greatest
: impact on rifle accuracy?

Primer uniformity is probably at the top of the list.  This is about 60%
of accuracy.  But it matters more as the range gets longer.  Non-uniform
primers mean a greater velocity spread which means the vertical stringing
at the target will be greater.

Case length doesn't matter much.  As long as the mouth is square with
the case axis, case length can vary 10 to 15 thousandths of an inch and
accuracy will still be excellent.

Necks should be reasonably uniform in wall thickness, like no more than
a .0005-in. variance.  This helps keep the necks straight when the cases
are resized.  And they should not be sized too much.  If they are, the
bullet seating pressure will be too high; too much tension will cause a
higher spread in velocity due to the normal variable incountered as each
bullet needs a different amount of force to push it out of the cases.  If
neck tension is minimum, the spread of the force to push the bullet out
gets lower resulting in a lower velocity spread.

Case weight variance plays a somewhat important part.  Heavier cases have
less volume, hence slightly higher pressures and velocities for the same
set of components.  A 1% spread in case weight is typically good enough
for best accuracy.  Any more than that doesn't seem to make any difference.

Primer pockets and flash holes should be uniform.  Pocket depth needs to
be consistant so each primer has the same pre-load; more uniform ignition.
Flash holes need to be the same diameter so the same flame properties are
transferred to the powder.  But these two things only make about a 1/16th
MOA difference in group size.

Case body wall thickness helps too.  They shouldn't have a spread of more
than about .003-in. for 30 caliber cartridges; .002-in. for 22 and 24
caliber ones.  But again, this only has a small effect, like about 1/8th
MOA or a tad less.

Powder charge weight variance can also cause more velocity spread.  But
just as important is powder type and charge weight.  It's been my experience
that for a given powder, there's two charge weights that tend to produce
the best accuracy; one at about maximum, and one several grains less.  A
chronograph is needed to check the velocity spread to determine this.
Charges with no more than a tenth grain variance is plenty good enough.
Primers typically cause a greater difference in velocity spread than a
tenth of a grain of powder.

Bullet seating depth also has an effect on accuracy.  Best accuracy is
usually going to happen when the bullet contacts the lands.  A lot of folks
are reluctant to do this as they claim max pressures will be higher.  Well,
they're right, but cutting the powder charge a few tenths of a grain will
reduce that pressure.

Bullet concentricity is important, too.  In a .308 Win. for example, if
the bullet runout is more than about .003-in., the groups will start to
open up a bit.  If it's more than about .007-in., they probably straighten
out as they enter the leade; I've not seen any more accuracy reduction with
such rounds.  The more a bullet has to jump to the lands, the straighter it
needs to be.  But bullets that are seated out far enough to be pushed back
into the case a few thousandths as the bolt is closed can have a bit more
runout and be accurate as compared to bullets that jump a ways to the lands.
A square case mouth probably does more for letting the bullets seat straight
than most other things.

It's easy to get good cases, bullets, powder and tools to assemble them.
But the hardest thing is getting good, uniform primers.  Primers vary
quite a bit across several lots; some much more than others.  For ranges
of 200 yards or less, there's not much difference between primers, like
about 1/4 MOA in the groups they can produce for the most part.  When
longer ranges are used, primer uniformity becomes more important.  A recent
batch of match-grade ammo (about 300,000 rounds) was loaded from the same
lots of cases, bullets and powder.  Neck tension was quite uniform.  Primer
pockets were not uniformed nor were flash holes drilled to the same size.
Bullet runout peaked at about .004-in.  But several lots of primers were
used.  Some loaded lots of this ammo would shoot 2.8-in., 20-shot groups
at 600 yards.  Other lots would shoot 20-in. 20-shot groups at the same
range.  The difference was in the primer lots; some were very uniform,
others were not.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: [RELOADING] What makes Bench Rest Primers special?
Organization: Hewlett-Packard Fort Collins Site

`Benchrest' primers are typically more uniform in their ignition
characteristics than `standard' primers.  The process of mixing the
lead styphnate (the explosive), glass frit (the microscopic glass
particles that act as micro-anvils for the styphnate to compress
against) and a couple of other things is a kind of `black magic.'
About two quarts of this priming mixture is mixed together for each
lot of primers.  Getting the mixture homogenous (uniform percentages)
throughout the gooey mixture is difficult.  This mixture is spread
on a plate with little recesses in it that are the shape of the
primer pellet.  Getting exactly the same amount in each little round,
deep hole is also a type of `black magic.'  The mixture is much like
putty and a large putty-knife like tool is used to force the mixture
into each hole where it's left to dry.  Then the dried primer pellets
are punched out and put in primer cups, topped with a sealer, and
finally the three-legged anvil is pressed in place.

Interestingly enough, some folks do a better job of mixing and spreading
the mixture than others.  Within each lot of several thousand primers,
there's bound to be differences in the ignition characteristics from one
primer to the next.  As more care is needed to make `uniform' primers,
they usually cost more.

By uniformity, I mean the consistancy of velocity they produce.  Velocity
tests of the bullet is about the best test of primer uniformity.  Some
very uniform lots of primers will produce a velocity spread of only 15 fps.
At the other end of the spectrum are primers that produce velocity spreads
of 100 fps, or more.  Some folks have tested primer uniformity by shooting
BBs from a primed case (no powder) in a 17 caliber barrel; primers that
produce low velocity spreads with BBs do the same with powder and bullets.
Uniform primers tend to produce more uniform pressure curves, too.

Alas, not all the `benchrest' primers are as good as they're marketed to
be.  Many times a standard primer will be more uniform than benchrest ones.
And some makes of benchrest primers aren't as uniform as another make of
standard primer.  Even some standard primer brands are more uniform than
any benchrest brand.  Some benchrest primers are hotter than their standard
versions for the same make.

In many accuracy situations, a milder, standard primer will produce better
groups than a hotter benchrest primer.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Accuracy via microprocessor control ?
Organization: Hewlett-Packard Fort Collins Site

Randy Howard (jrh@mustang.us.dell.com) wrote:

: I'm curious what you mean by "mild"?

By mild, I mean primers that produce just enough heat to properly ignite
the powder.  As primer brisance (heat/energy) gets higher, it also gets
less repeatable from primer to primer.  Competitive shooters have found
that the milder primers give both better velocity uniformity and accuracy.
But they aren't after every last fps of speed nor ft/lb of muzzle energy;
just putting all fired shots in as small a group as possible.

: A lot of reloading articles I have
: read seem to indicate that it's better to use magnum primers in all
: rifle cartridges (starting with a lower powder charge than normal and
: working up of course) because they will result in more consistent ignition.

This is true with most ball powders, the type most folks tend to use in
rifles because they meter very uniform charge weights from measures.  But
when accuracy is the objective, extruded powders are used and so are mild
primers such as Federal 205M, RWS small rifle, Rem. 7-1/2 BR small rifle
primers.  The mildest large rifle primers are Remington 9-1/2 standards and
RWS5341s and they are also the most uniform of large rifle primers.  Some
lots of Federal 210Ms are very uniform and others are not; these are not very
mild primers.

But then virtually all folks writing reloading articles for magazines have
no real knowledge of what they are talking about in the first place.  When
you consider that most of 'em don't have what it takes to shoot 1/10th MOA
groups at 100 yards nor 6-in. groups at 1000 yards, how in the heck can one
consider their information worthwhile regarding accuracy.  They put
enthusiasm and egos in print; not reality.  But they get paid for it in
spite of not having any skill or knowledge in putting together a valid set
of tests to produce statistically significant results, then publish those
results in an unbiased manner to boot.

: It sounds like you feel the opposite is true.

So do hundreds of others who have observed the results of lots of primer
makes and types being used by the hundreds of thousands of rounds fired.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Accuracy via microprocessor control ?
Organization: Hewlett-Packard Fort Collins Site

Robert Lewis Glendenning (rlglende@netcom.com) wrote:

: As I understand it (dimly), accuracy is strongly controlled by
: uniformity of muzzle velocity, among other factors.  This is inherently
: difficult to make uniform because of variations in the rate of powder
: burning.

In reality, primers are more responsible for velocity variations than powder
is.  Next in line is case neck tension variables.  Third is the distance
variables the bullet jumps to the rifling.  Powder charges, even if they
vary a couple tenths of a grain about, say, 45 grains, are very uniform
in their velocity producing efforts.

Some powders tend to cause more muzzle velocity variations than others.
Extruded powder tends to be the most uniform; both benchrest and highpower
competitors favor this type over ball powder for this reason.  And extruded
powder tends to give more uniform velocities over a wide ambient temperature
range than ball powder does.  Some powders tend to produce more uniform
muzzle velocities than others as bullet and charge weight changes.  That's
due to their expansion ratio and burning rates relative to the bore diameter
and barrel length.

When the most mild and uniform primers are used, muzzle velocity standard
deviations can be kept to 5 to 7 fps.  That's a muzzle velocity spread
of about 16 to 22 fps; darn well good enough for even the most demanding
shooter.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Accuracy via microprocessor control ?
Organization: Hewlett-Packard Fort Collins Site

J. Spencer (J.M.Spencer@newcastle.ac.uk) wrote in response to my comments
preceded by : #:

: #In reality, primers are more responsible
: #for velocity variations than powder
: #is.

: How, and why?

Because of the way the priming mixture is prepared and put in pellet moulds
then put in cups, anviled and sealed.

: If the manufacturers can get powder to burn consistently,
: and we can get consistent charges so that their effect is minimal, why
: can't the manufacturers produce consistent primers?

Primer mixture creation and processing is almost a `black magic' operation.
Few folks can uniformly put the putty-like substance in a totally
homogeneous form that's very uniformly mixed.

: And a related question: how do know
: that it *is* the primers, how has it been measured?

Measured by velocity standard deviation, using various primer makes/types
with different powder charges show that primers have the greatest effect
on uniforming velocities.

: That is one variable which we can eliminate, can't we?

Yes. Seat the bullet to where it pushes back into the case when it jams
against the leade as the bolt is closed.  That uniforms bullet jump as
leade/throat wear lengthens this part of the barrel.  You may need to
increase the powder charge weight by about one-tenth of a grain every
1000 or so rounds to keep velocity at the same level; otherwise it will
drop several fps as the leade/throat dimension gets greater.

: #Some powders tend to cause more muzzle velocity variations than others.
: #Extruded powder tends to be the most uniform; both benchrest and highpower
: #competitors favor this type over ball powder for this reason.

: It's just a bugger that it doesn't meter as well, eh Bart? :-)

Yes, but a charge weight spread of up to two-tenths of a grain doesn't seem
to matter much.

: #When the most mild and uniform primers are used, muzzle velocity standard
: #deviations can be kept to 5 to 7 fps.  That's a muzzle velocity spread
: #of about 16 to 22 fps; darn well good enough for even the most demanding
: #shooter.

: Really? I'm genuinely surprised at that (not to imply I'm skeptical,
: just surprised). Which primers do you recommend (for 243 and 30-06 if
: it's relevant)?

If you can afford 'em, use RWS 5341 primers.  Otherwise, Remington 9-1/2
standards are also very mild and work very well indeed.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Primer types  (was Re: Accuracy via microprocessor control ?)
Organization: Hewlett-Packard Fort Collins Site

Randy Howard (jrh@mustang.us.dell.com) wrote:

: What extruded powders are used by the bench rest crowd with these primers?

H322 and IMR4198.  There are others like IMR4895 used with the .308 Win. and
light, 135-gr. bullets.  I don't remember what all of 'em are.

: In particular, which would be appropriate for .308 and .300 WM?

For .308 with bullets lighter than 160 grains, use IMR4895, Re-15, N140
or Hodgdon's upcomming powder which is from Australia called Mulwex AR2208
but Hodgdon will assign their own number to it.

With bullets heavier than 160 grains in the .308, use IMR4064.  IMR4350
works well with 200-grain bullets in the .308.

30 caliber magnums tend to do best with IMR4350 or Re-19.

: Also, since
: they don't meter as well, do you hand measure each charge, or is there a
: different type of powder measure that is used in this case?

Any method to keep charg weight +/- 0.1 grain is good.  Some folks use
electronic measures that dribble near exact charge weights; others just
throw from a measure then dribble up to the desired charge weight.

: I'm guessing
: here that if you don't use an extruded
: powder for reloading, then you'd want
: to use the hotter primers instead.

Depends on the powder's burning rate.  Best accuracy usually comes from a
powder that's fast burning enough to produce acceptable velocity.  Just use
the mildest primer that gives velocity standard deviations as low as possible.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Best long range rifle primers?
Organization: Hewlett-Packard Fort Collins Site

Bob Boardman (boardman@cobra.unm.edu) wrote:

:       Why is it that mild primers produce better accuracy than hotter
:   ones?

The reasoning is that the powder is ignited a tad more gently.  When
this happens, the front slope of the pressure curve is less steep.
Which means the bullet is pushed a tad more gently into the rifling.
And that tends to deform it less.

:   One would suppose that it might be due to more uniform ignition
:   of the main powder charge.  However, as the thread about ball vs.
:   extruded powder concluded, you want the bullet to exit the barrel as
:   quickly as possibly after the trigger breaks.  One would think that
:   a milder primer might actully result in a slightly delayed ignition
:   of the main charge and thus increase the length of time the bullet
:   is in the barrel, which is contrary to the observed accuracy results.

The difference in barrel time between mild and hot primers is probably
too small to be noticable.  Very mild primers have been used in the
.243 Win. and 7mm-08 to win many matches, including the Nationals, as
well as set some records.  These are small rifle primers; much, much
milder than large rifle primers.  With the .308 Win., small rifle primers
work great, and may well be the most accurate method, at ranges up to
300 yards.  They don't do well at longer ranges with heavy bullets and
maximum powder charges.

:       Also, I'm curious how the "standard" size of the primer flash hole
:   was determined?  Has anyone ever done experiments with smaller flash
:   holes to see if this would have the same effect as a milder primer?

It's hard to get cases with smaller than standard size flash holes.  That
size was probably determined by some trial and error processes near the
turn of the century.  Virtually all cases have flash holes about .080-in.
in diameter.  PPC benchrest cases have smaller ones as I remember.  But
a smaller flash hole means the decapping pin must be smaller, hence
weaker and may oft times break.

BB

 






































































































































































































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